Winter Layup - 1995 Ducati 900 Supersport

[OddDuck]

Been clocking a few hours up in the garage over the last few days, covered quite a bit of ground while trying to sort out what's happening with the rough running.

First, I tried the usual 3,000 mile service, paying particular attention to valve clearances in case these were contributing to running problems. They've all loosened up a bit, probably due to the MBP retainers crushing up by a thou or two. I also found a hose clamp sitting skewed on the horizontal cylinder's carburettor output, enough to cause a minor vacuum leak. This might have been why spark plugs from this cylinder were coming out bone-white. The AFR gauge is on the vertical cylinder exhaust and wouldn't have shown a lean mixture on this cylinder.

Along the way I found out something unpleasant about the Taiwanese-made, plastic quick release fuel line couplings: sometimes they leak. It's fixable. If the 7 x 1.5 O-ring is carefully lifted out, the flash line from the mould can be seen to run right through the O-ring's inner crush diameter. Some very careful work with a needle file can smooth this out and then it's OK. That said, these fittings are OK but not great, if someone can recommend a better alternative then I'd appreciate a heads-up.

Anyway... went out for a ride, no improvement whatever. Damn. Back to the garage.

I got the oscilloscope out again and spent much of a sunny afternoon annoying the neighbors. About the only usable result from the photographs is shown below. There seemed to be a lot of trouble with reliable triggering, connecting lead wires to plugged-in pickups, etc etc... but in the end I think I have a result. The horizontal cylinder pickup coil looked OK when tested unplugged, with the motor cranked by the starter, but as soon as the CDI was plugged in and the ignition energised it would not generate any significant signal. The vertical cylinder pickup worked just fine regardless.

As a last resort I tried something I'd read of on the Ducati.ms forums - I fitted braided shielding to the pickup cable. Some people out there have been keen enough to fit shielding right through the gland and into the engine; for the purpose of testing (and sanity) I stopped at the crankcase. The shielding is pure braiding and heatshrink, there's no solder connections between the legs or to the lead wire used to ground the braid. Oxidation will kill it in a season or less, but for testing it'll do.

I tried this tonight and was surprised to see how much of a difference it makes: the bike is perceptibly smoother and sounding better, even just revving it on the stand with the exhausts pointing out of the garage. To carry to the test as far as possible, I took the strobe gun and tried it on both cylinders.

What a difference. The vertical cylinder idles at the reference mark and advances cleanly to the full mark, with the strobe gun keeping pace the whole way. There were no missed flashes, unlike previously.

The horizontal cylinder was the same story as before, though. The idle is off the reference dot, with the engine a few degrees advanced already, and the strobe gun dropped out as soon as RPMs were increased.

I also borrowed a 100V Megger from work and tested the pickup coils insulation resistances to ground. Neither failed, but the test that was really needed was seeing output from the pickup under real operating conditions - i.e. in ac voltage generation, with the coil loaded as it would be in normal use - and the oscilloscope work covered that already.

The conclusion I'm now operating on is that the horizontal cylinder pickup coil is stuffed. The shielding was a very worthwhile improvement and I'd recommend doing this on any old bike running inductive pickups and plain cabling. It can't rescue damaged components, though.

As to why the pickup coil has failed - my best guess is that inside an engine, this is inevitable given enough time. Heat, oil (with acidic combustion byproducts in it), vibration, plus constant electrical loading of what's probably very fine coil wire, it'll add up after 22 years. Either the insulation has been damaged by the oil and heat, or the wire has thinned somewhere and can't carry the load any more, even though the resistance still tests fine on the multimeter.

I also had a look at the Hayne's manual, courtesy of my local public library. I'm not so keen on buying one anymore. There's very little useful information in there for someone in my situation, when Haynes write their manuals they rebuild a near new bike instead of a high mileage and old one.

[pete376403]

Seeing as you have one good cylinder and one bad one, can you not swap components one at a time until the problem moves?

[OddDuck]

Seeing as you have one good cylinder and one bad one, can you not swap components one at a time until the problem moves?

Yep, that'd be the normal procedure, but I don't think I'd have picked which pickup coil it was by doing that. It's also hard work - I'd have to get inside the cases to swap the pickup coils over, if that's even possible with made-to-length wiring like they use.

The other thing is that nothing's actually stone cold dead. It's just that stuff has slowly gotten a bit sick. If it 100% didn't work then it'd be very possible to swap things over and see if moving something brought a dead cylinder back to life. It isn't like that though, it's still running on both, it's just that it's running really badly.

I'd always thought that the horizontal cylinder was running fine while the vertical struggled, it took using an oscilloscope and the strobe gun to show it was actually the other way around.

I'm happy with the result I got, order to Stein Dinse is already away.

[Voltaire]

Liam has those too.

http://www.fastbikegear.co.nz/index.php?main_page=product_info&cPath=706_1635&products_id=6792

I haven't bought any bits of Stein Sinse for a while but I gather their minimum post was pricy.

You can really chase your tail with ignitions/carbs. I spent a lot of time getting my Mk2 lemans sorted even swapping carbs from one side to the other,

only to find most of the brass worn....but no enough that you could see it.

Ignitions are the same, replace the lot.

[OddDuck]

Liam has those too.

http://www.fastbikegear.co.nz/index.php?main_page=product_info&cPath=706_1635&products_id=6792

I haven't bought any bits of Stein Sinse for a while but I gather their minimum post was pricy.

You can really chase your tail with ignitions/carbs. I spent a lot of time getting my Mk2 lemans sorted even swapping carbs from one side to the other,

only to find most of the brass worn....but no enough that you could see it.

Ignitions are the same, replace the lot.

FastBikeGear: check the little "available stock" tag before buying. I've been keeping tabs on those pickups and they seem to have been on order for over a year... No stock in country. Currently I'm waiting on a few components to be machined up for the upgrade to Ignitech & Hall Effect, and it's been 5 weeks since order placement now.

In the meantime Stein Dinse charge 40 euros for postage regardless of order size, so you're right, it's not exactly free, but they've been very reliable in terms of getting goods to me in a few weeks. Summer is just around the corner. It's wasteful buying two complete (separate) ignition systems, but I've learned the hard way about open-ended waiting times on orders.

In terms of fault finding and tail-chasing - I agree, once the bike's 20+ years old and you start having hard-to-trace problems with running, you can really chase your tail with this stuff. Swapping old components around really only works if there's a large difference between them.

After the work I've been through over the last few years with the Ducati's running problems I also agree with the idea of replacing the lot in one go. 20+ years old... as soon as one ignition component is known walking wounded, the others aren't far behind. It'd have been horribly pricey to do the whole thing in one hit but I'd have saved maybe a couple of hundred hours in the garage, not to mention rides spoiled or cancelled. Hell, chances are that the bike's been plagued with bad ignition since I bought it and I've simply never seen one running properly to compare it against.

I've been there with worn brass in carburettors as well, had that with the original Mikunis emulsion tubes going oval around the needles. I was lucky enough to be able to see it by eye, but it wouldn't have been easy to measure with normal garage tools unless a set of 0.1 stepped drills was available as plug gauges.

All that said, what I tried in the few posts above was a way to diagnose ignition systems without swapping anything and without spending a fortune. A 'scope, probes, and a strobe could be had for around $200 (there's a few oscilloscopes floating around on TM these days). Between the oscilloscope and the strobe gun, I've seen that the system has a problem with radio frequency interference (and probably always has) and that a pickup coil can test just fine according to all the workshop manuals and yet still have issues when running. So I think this stuff is worth doing.

[OddDuck]

Replaced the pickup coils. Pretty straightforward really, just a couple of notes for anyone else doing similar.

- The cover removal tool is necessary, so is taking the kickstand bracket off since it'll foul the cover otherwise.

- The pickup wires can be pulled out of their box headers (at the CDI's) by using a fine flat-bladed jeweller's screwdriver. You don't need the specific Ducati tool.

- Before doing this (apologies for the caps) LABEL EVERYTHING. H for horizontal, V for vertical, red, white, yellow, black. Get the sharpie out and label headers. It's very easy to swap things around by mistake on reassembly.

- Ducati labelled wiring colours inside the engine covers, which was a nice feature. There's also an offset scale cast into the pickup coil mounting bracket, I think each tooth marks 2 degrees.

- Ducati's OEM pickups come with good wiring and cabling, it's why I chose these over the aftermarket. There's a proper moulded-on silicone rubber hose to go through the gland, for example.

- I used an impromptu feeler gauge made out of a few bits of brass shim, taped together at the specified 0.7mm +/- 0.1 clearance. The reason for brass was that it's not affected by magnetic pickups, the reason for the clearance (when I've run tighter in the past) is that pickup coil voltage increases with RPM and I didn't want to run a risk of damaging CDI circuitry.

- Unfortunately it'll take a few goes back and forth to get pickup clearance right, this will involve turning the engine over a couple of times and loosening and retightening the bracket bolts.

- it's easy to skew or cross-thread the cable gland retainer on reassembly. It'll feel like it's compressing the rubber washer and ensuring a seal, but it's just crossed. Keep an eye out for this and check it's parallel on reassembly.

Anyway, I got everything back in place, fitted new shielding (but only over half the cabling, up to the Y split - more about this later), fired up and the bike started without issues.

[OddDuck]

Carrying on with the issue of rough running... I'd taken the bike out for a quick spin after pickup coil replacement and the vibration hadn't got better. It was worse.

What to do, what to do... after some thinking, I pulled the spark plugs to check combustion and found them black. Bike's running super rich. Bike's also very, very loud. This has happened before, and I remembered that I haven't repacked the mufflers in a long time. On checking the maintenance logs, it hasn't been done since the engine rebuild (at least), and that was 14,000 miles ago.

Getting into the cans is pretty straightforward, the photos tell most of the story. A couple of pin punches helped with the rivets, the little one is for knocking the center pin through before drilling.

The packing has thoroughly filled up with carbon. I'm not sure if this is normal or indicates vastly rich tuning - anyone? Anyway, the experience has been that this affects engine behaviour quite strongly, and I'm thinking that it makes sense to schedule a re-pack at every other oil change.

[OddDuck]

Mufflers repacked. Went for a test ride, bike ran better, vibration issue's still there but has roughly halved.

Just a quick note about using the crowbar to get the end caps off - don't do this on shiny new mufflers - the crowbar and mallet technique has a distressing habit of jumping and biting. I've put a few fresh scratches onto the stainless piping and outlet. It's not the end of the world with these battered stock mufflers, but it'd suck to have this happen with nice new ones.

So, next step - is there dirt in the carburettors, with one cylinder running lean or rich? So I pulled the carburettors off for an external wash prior to blowing carb cleaner through the jets.

External washing was done on the cheap, with an old paintbrush, a laundry sink filled with warm water and dishwashing liquid, and inlet and outlet pipes masked off with gloves and stretch ties to prevent water ingression. I didn't submerged the bodies, just held them above the water. Dishwashing liquid was used because I knew it wouldn't hurt the aluminium, I've found that a lot of the more aggressive degreasers around will tend to attack the metal if they're on for too long. There was some dirt under the inlet trumpets and it was getting close to the slow air jets and main air jets, despite claims that gaskets are only needed for ram air applications, I think it's probably a good idea to seal these to the bodies properly if possible.

The insides turned out to be surprisingly clean considering the mileage. It was when I'd unscrewed the slow air jets and the idle mixture adjustment screws that I found the misadjustment, and the reason for it... the idle mixture adjustment on the horizontal cylinder was nearly screwed all the way in. The startup carb bowl heater element was sitting very high in the carburettor bowl well. I think vibration had been working to push this heater upwards. It had then been hitting the screw and bumping it.

The heater can push the screw, it can't pull on it, so over time it'll force the adjustor further and further upward. This is entirely due to my rough build. There's a retainer plate to stop the heater element falling down. There isn't anything to clamp that element securely in place, or prevent it moving upwards. I'm going to have to modify.

Anyway... carburettors back onto the bike (the quick release fuel hoses helped greatly with this) and test rode again. Further improvement, still hasn't fixed the problem though.

At this point I went and had a look at interference in the ignition system again and finally noticed something I should have seen much earlier: I'd routed the HT leads within a couple of centimeters of the horizontal cylinder's CDI unit. This isn't good practice as far as RFI interference and cross-talk goes. I re-routed as per the photos, cable ties to the coil mounting brackets and split fuel hose to help cushion the HT leads. It's an improvement of only 3 to 4 centimeters, but at this point every bit helps.

[OddDuck]

A bit more work on RFI shielding for the ignition system - I'd tried this earlier, with some success, before changing the ignition pickup coils. One of the issues with getting the old shielding off had been that I'd used adhesive-lined heatshrink to fit the braided sleeving. It went on fine; it was a nightmare getting it off again. This time the construction was:

- Unshrunk tubing under the braid, to protect the pickup coil wiring against loose strands from the braid
- the braid itself
- sparkie's tape to secure braid ends to the undertube
- auto wire, stripped and wrapped around the braid, to make the electrical connection
- more sparkie's tape over that to wrap the, ahem, 'connection'
- high temperature plastic overbraid
- yet more sparkie's tape over the ends of the overbraid

Apologies, the photos are out of order - look at filename numbers for the sequence.

The Y-split complicated things, and I didn't quite have enough braid to properly cover the joint. Shields need to be as close to continuous as possible. Note that there aren't multiple grounds - the wires come back to one point on the shield and then are earthed to the frame by one link only. This is to prevent loops forming in the shield and thus turning the braid into a pickup and an antenna, coupling noise in more effectively than if there was nothing there at all.

It's not going to last. Weathering, heat and vibration will kill this within a year. The point to this is to see what effect it has, and then if it works, to make something durable along the same lines.

Short answer: it helps, but it's not a complete shield. I haven't got anything over the CDI's or the lines to them, for example. Slight improvement when running.

During my reading about shielding, I turned up this PDF:

http://www.analog.com/media/en/technical-documentation/application-notes/41727248AN_347.pdf?doc=CN0397.pdf

It gets very technical and it raised a lot of thoughts... first of which is that the layout of the ignition components on the Supersport really isn't the best. Coils are placed immediately next to CDI's. Pickup wiring is run close to HT leads, in the original setup. That sort of thing. It packages nicely. I don't tend to see Japanese bikes laid out like this, the CDI is usually under the seat, while the coils are close to the engine.

One of the basics of avoiding interference gremlins is that distance is your friend. Get as much separation between components as possible.

Another issue that the PDF raised was the possibility of magnetic interference from the coils themselves - like most ignition coils, they run open laminations, so there's a free magnetic field around them. This is much harder to screen out than high-frequency RFI - a dinky piece of nickel-plated copper braid simply won't do all that much. The paper pointed out that steel is the best material, and it's got to be reasonably thick to get any sort of attenuation. Several millimeters thick. The bright side to this is that I don't need that much attenuation (a few dB would be enough) to get an improvement.

Something else I'd read concerned the idea of using braided shielding on HT leads. It's been tried, off and on, for well over forty years. Short answer: it starts out well enough, but any degradation in the HT lead insulation and the shielding turns the lead into a capacitor. Spark starts being lost to the shield. The second problem is that the shield itself, if connection to engine ground is lost, will run at full HT voltage. This can be lethal. Basically, don't shield the HT lines, shield everything else.

So the bit that I'd like to try next with this is to make up some sort of steel shielding for the pickup lines, where they run close to the ignition coils, and a pair of steel boxes for the CDI's. Everything will have to be grounded to one common point, so there's be a secondary network of wiring as well.

[pete376403]

Run the wires through a steel tube? Does it have to be steel? Would copper -easier to bend- do it?

[OddDuck]

Thanks for that idea. Copper's good (excellent for RFI) but steel's about twice as effective for anything magnetic. Anything conductive will work, given enough thickness, but anything magnetically permeable works best. Which is why I've fixated on steel, difficult as it is...

The idea I've been toying with is to machine up a Y-branch housing (steel) and a bunch of fish spine beads (also steel) and then find a way to connect them mechanically and electrically, then shield the lot against the weather. It's big work and at the moment I can't think of a way to guarantee longetivity.

The alternative (as you suggest) is piping, in that case copper would be a hell of a lot easier to play with as a first try. Certainly 1mm-ish wall thickness copper would be a big step up from the braided shielding. It's also much more likely to age well... One piece construction, can be covered in heatshrink, the ground lead will solder to it without issues... it's got a lot going for it. Well worth a try as a first cut, if this does the trick then there's no need to spend weeks making beads by hand. Thanks again Pete.

The other path to take is separation - get the CDI's and pickup leads as far away from the coils as possible. That option's still open but having heard the motor finally synchronise sort of properly (with the earlier attempt at shielding) I'm curious; can it be done?

[OddDuck]

I've spent the last four evenings moving the oil cooler, as per Kickaha's suggestion - the idea is to provide a flow of warm-ish air to the carburettor bodies while riding.

I fabricated a pair of split-clamp brackets, intended to attach to the lower frame cross-bar, and finally got the oil cooler hoses from Improved Racing out. There was a fair bit of fiddling to get everything into a place which would work. The brackets aren't welded-on frame tabs; this turned out to be just as well. This way and that, rotated forward, back, into the frame cavity or out of it... it took quite a few goes to get to a position that I think will work. I've placed some rubber under the clamp brackets to protect the frame paintwork.

One of the unexpected constraints was providing for front wheel movement under a bump - accomodating the wheel isn't so hard, but one of the brake hoses moves rearward quite a bit. It wouldn't be the best to have this contact either the oil cooler or the edge of the air chute.

The air chute (a cheapo bit of sheet metal, shaped like a ski jump) is probably a work in progress, I can see this going through several iterations. The oil cooler simply wouldn't go to a place where it was in line with carburettor bowls and slipstream, so some kind of an air duct had to be used. It's meant to do three things:

- keep slipstream air from impinging directly onto the carburettor bowls
- guide oil cooler-warmed air to the carburettor bowls
- keep the rec-reg unit alive, by guiding hot air away from it during low speed traffic. Uprising air at the back will tend to suck cool air in at the front instead of letting air rise vertically off the front surface.

Finely-controlled air flow it isn't, there'll be all sorts of spill over edges and turbulence, but before it works well it has to fit into a compartment that is now a plumber's nightmare.

I replaced the anti-vibration mounts. I'd been concerned that the old ones would be corroded into the original valve cover and I'd rip them up while trying to unscrew them, but it turned out to be necessary anyway. The old ones had started to split and fail, with the rubber separating from the metal ends. It wasn't obvious with the oil cooler still in place and some dirt covering up the cracks.

The oil cooler hoses themselves have turned out to be far too long. I've had to place them where I could get them to fit. This is entirely my fault, measuring by guesswork in situ turned out to be a bad technique. Hose flex and placement turns out to be very dependent on length; a couple of centimeters can make a huge difference. I'll try ordering a roll of hosing, fittings etc, and making up my own oil cooler lines later.

One note for anyone else replacing oil cooler or hoses on an old engine... I had a nasty surprise. The aluminium nipples on the cooler had corroded, just behind the tapered sealing faces. It'd be very easy to get corrosion / aluminium particles / anodising etc into the new hoses by mistake, and this circuit is right in line with the main bearings and conrod shell bearings. I've ended up using rags, cotton buds, washing the oil cooler out etc, but it's still a risk. It may be a very good idea to order in new nipples as a precaution before starting this sort of work.

Right, time to go for a ride and see how it worked out. Shielding work is still on the list, I'll have a crack at that a bit later on.

[BMWST?]

i admire your tenacity and thoughtful approach sir.Always an interesting read .

[AllanB]

Nice job. Better place for the oil cooler as well - no crud from the front wheel and in a more direct flow.

[OddDuck]

Thanks guys... unfortunately although it looks like the oil cooler is helping with keeping the mixtures constant while riding, it's doing little or nothing for the vibration issue.

I'd realised, while checking the oil hoses for leaks, that I'd left the tail end of the shielding on the pickup coil leads open. It's been scratching against one of the oil line banjo bolts, giving an intermittent, high resistance connection at one end of the shield. This is a no-no because it sets up a loop in the shield itself. I'd done a quick and nasty job of insulating it, using a piece of flat rubber sheet and some cable ties (was in a hurry for an upcoming ride), but this made no difference.

I've been trying one thing after another to isolate what's going on. It's been successful in the sense of now I know a few things that aren't causing the problem. Tried so far:

Engine to frame bolts: torques checked out OK. Nope.

Grounding my new-ish steel battery box: Nope.

Pulling, stripping and checking the primary leads to the ignition coils against insulation failure and cross-talk: nope, even at 20+ years, the wiring's still OK. I re-covered that part of the loom with heatshrink tubes over individual wires (to get extra insulation) and re-tried, but no change.

[OddDuck]

Carrying on...

Carburettor balancing on the flatslides is normally done with a mechanical gauge (the shank of a small drill for example) but I also checked it with vacuum gauges, normally seen used on CV's. No significant difference between them to indicate anything wrong with carburettor balancing. It was interesting watching the needles waving around with the bike running, though.

I realised that the existing setup had the HT leads directly contacting the underside of the fuel tank - damage can be seen on the outer sheathing of one in the photos. It had been like that since I'd installed the replacement battery box. I had a play with the setup and realised that there wasn't an issue with installing the coils HT lead down, since I'd left a gap in the right place. This also shortened the HT leads. So - tried running the engine - no improvement.

I bought some new HT lead and tried fitting that. Still no joy. So it wasn't degradation of the existing leads.

A quick check of play in the main bearings - that's possible via the crank turning tool and the crankcase cover - but that wasn't it either.

I'm growing convinced that the issue is cross-talk in the ignition. The coils are talking to each other and I'm getting sparks on both cylinders simultaneously, or so I think. It's also slowly getting worse, despite everything else I've been doing. The timing lamp was tried again briefly (on the vertical cylinder) and would only synchronise at idle. At any faster engine speed, the lamp would drop out. It wasn't that bad when I'd tried it a week or so earlier.

While riding, engine behaviour isn't any better - I'd get occasional backfires through the induction, and the engine would drop out completely for a revolution or two when under sudden acceleration. The vibration, curiously, is mostly there but sometimes smooths out, particularly after the bike's been stopped for a while with the engine shut down.

So... last roll of the dice, really, after this I'm out of ideas for now... my current theory is that the CA Cycleworks coils have suffered some kind of gradual insulation failure. This is very early, these coils are only around three years old. Anyway, what I'm guessing is happening is that the high voltage secondary on coil A is leaking voltage, either to the coil mounting bracket or somehow is cross-talking within the existing primary wiring. The leakage voltage either then couples directly to the secondary on coil B, or it energises the primary which then fires the secondary... anyway, a spark on one couples across and fires the other, too.

I'd made a list of crank positions for a full 720 degree cycle. There are four spark plug firings - one intentional firing for each cylinder, and one wasted spark each as well. If I look at where they cross over, there's one occasion where a cross-fire would catch the horizontal cylinder during its compression stroke, and another time where a cross-fire would ignite mixture in the vertical cylinder during induction. These would be weak sparks and would be swiftly quenched, but still... there'd be a bump on one and a burp on the other, hence the vibration and the intake backfires.

For the record, none of this would be a problem on a 360 degree parallel twin. Leakage spark would be lost in the intentional spark, since they'd happen at the same time. That's if they use separate coils of course, it might be a double-ended system, I don't know. This cross spark business is a V-twin or triple problem.

I haven't yet tested. Maybe there's a voltage turning up on the coil mounting bracket, or a look at behaviour on the primary side of the system will show something. I'm not sure yet how to test - if there's a secondary voltage present it may destroy the multimeter.

I did some reading today about dielectric insulation breakdown and it came to these salient points:

- enough voltage applied and anything breaks down
- the effect gets more powerful with higher frequency
- impurities in an insulation material lower the breakdown voltage - like, say, moisture ingression
- once a path is established through solid insulation (electrical trees etc form), it stays. Solid insulation doesn't heal.

It may be possible, as a test, to remount the coils on insulating spacers and see if that changes things. If there is a leakage path through the mounting bracket then that will tell me something, at least.

[OddDuck]

Insulating spacers tried - see first two photos - possibly a very slight improvement but nothing conclusive.

Lots of chasing my own tail going on with this problem, lots of trying stuff and getting nowhere... it was only purely by chance that I saw the hole in the CA Cycleworks coil potting. There's been some kind of a blowout around one of the Low Tension (LT) positive terminals.

Without testing beyond seeing, it looks like the HT side of the coil winding has been shorting directly into the primary side of the ignition. That's 30 kV looking to roam. No wonder there have been problems.

Right, replace coils... while I was at it I thought I'd sort out the nasty oil leak that's been forming on the front underside of the engine. My thinking with this was that the larger O-ring (sealing an oil return galley between head and barrel) had been fried. Horizontal cylinder head would have been running hot due to pre-fire during compression. I changed this seal out and reassembled the cylinder, then refitted exhaust system, inlet, fairings etc to the bike. That's about fifteen hours work but there's no shortcuts here. For some reason Ducati put the oil pressure feeds on the outside, where it's easy to get at, but not so with the drains.

On closer examination of the photos after the job was done, it looks like a worse problem: oil's been leaking out of the cylinder head spigot. It would have been carried to the top of the bore by the piston rings. The gunk path is quite clear. There's not really anything I can do about it now except to take the motor apart again and have a go at resurfacing the spigot. Somehow. Ducati do specify that it has to have a perfect surface, which might not be easily done in a home garage.

The extensive blackening on piston and inside head is what happens after lots of cold starts. It (mostly) came off pretty easily via scrubbing with a rag, a dishbrush and a witches brew of one part isopropyl alcohol to two parts white spirits.

[OddDuck]

Right, and now a result. This may be valuable information for other owners, I'm sure that this problem is wider than just my bike or even Ducati's in general. I didn't want to discuss this before I was sure.

Ignition's fixed.

Replacing the coils (with stock Ducati items) has helped, however I have finally understood a problem with the bike that's been there since day one of my ownership and have found a work-around solution.

There's a high resistance back to the battery, through the stock wiring loom, from the tops of the ignition coils. This resistance is important because ideally the battery absorbs voltage spikes off the tops of the coils. If there's impedance on the line back to the battery, a spike on the top of one coil will start to be shared, voltage and current divider-wise, between battery and the coil that isn't supposed to fire.

I measured the impedance on my loom by fitting an 80 ohm automotive relay coil where the coils and CDI units were supposed to draw their power and then connect back to earth. The system was powered up. I then measured voltage across the 80 ohm coil, and also voltage across the loom, from the top of the coil back to the battery terminal. I did it this way because having the loom powered up closes relay contacts etc, it also loads contact points up with realistic amounts of current instead of the tiny sensing current of a multimeter.

A look at the Ducati wiring diagram told me that this path - battery to tops of ignition coils - goes through quite a journey. There are multiple crimps, lengths of wire, push-together connectors, the main relay contacts, fuses, and the kill switch. Ideally the voltage across the loom should be as close to zero as makes no difference. It wasn't. I got 0.58 V across the loom and 10.7 V across the coil. Working out the resistance via V=IR, I(loom) = I(coil) and R(coil) was 80 ohms, it turned out that I'm running 4.3 ohms or similar in the main wiring loom.

4.3 ohms.

It doesn't sound that significant does it?

Unfortunately, with ignition coil primary winding resistance being 4.5 ohms, that works out neatly to nearly 50% of any noise on the 12V supply line coupling straight into the non-firing ignition coil. The resistance in the main loom has formed a voltage and current divider.

That brings me to Paschen's Law, the relation between spark gap, pressure, and the voltage needed to make a spark:

https://en.wikipedia.org/wiki/Paschen%27s_law

In a nice world for us bikers, it'd be easier to make a spark under compression. Unfortunately things go the other way. It's about 22 kV to make spark in an air-fuel mix at full compression, but only about 2 kV in a normal one atm pressure mixture of fuel and air.

This would mean that it wouldn't take much electrical noise to get a spark happening at the wrong time. To be sure that there isn't a false spark, the rejection ratio of the path back to the battery would have to be improved to the point where any surviving noise presenting to the non-firing ignition coil cannot generate 2 kV or more at the HT end of things. Reducing stray current will follow suit, and sparks also need current for their energy. So the voltage divider effect has to be reduced as far as possible.

I did this by simply taking the main loom out of the equation and fitting the fore-mentioned automotive relay in its place. The loom's ignition supply now runs the relay's switching coil. The relay has a direct, much shorter, path to the battery, and supplies coils and CDI's directly. The AMP Superseal connector was available through RadioSpares, although auto electrical places with access to the Hella network would have it too. The wiring shown in the photo isn't quite complete, I finished the reworked loom off with spiral wrap to protect against abrasion. Spiral instead of heatshrink was chosen because it'll come off again reasonably easily and also it allows breakouts.

This isn't just a Ducati problem. The arrangement of wiring running from battery, through loom, to nose of bike, kill switch on handlebar, then back through loom to coils, is pretty much universal as far as I know. A high resistance through this arrangement will affect any bike with non-180 / 360 degree ignition timing.

That's all V-twins, triples, unequal parallels, big bang fours, etc etc. The only bikes fundamentally immune are 360-degree twins and inline fours, because a false spark happens at the same time as a wasted spark.

From what I've seen so far, warning signs that this is happening are:

- occasional backfires through the induction system
- white spark plug on one cylinder, persistently near-fouled plug on the other (identical fuelling)
- exhaust sooting occurring on one cylinder (the one with the near fouled plug)
- lots of really nasty exhaust noise
- rough running, hesitation or stumble on throttle opening

Tonight's test run, incorporating a turn on the motorway, showed massive improvement in noise control and running. This was the best that the ignition has ever worked.

Unfortunately the vibration problem, while greatly reduced, has not gone. It's about 25 to 50% of what it was, enough to be alright on hands (mostly) but painful on feet and toes. I think there's something mechanically wrong with the engine due to false sparking happening halfway through compression. So, halfway there. Mechanical stuff is a pain but at least I can see what's going on.

[Kickaha]

There's not really anything I can do about it now except to take the motor apart again and have a go at resurfacing the spigot. Somehow.

fine valve grinding paste and lap it on

[OddDuck]

Thanks Kickaha - I'll try that the next time I have the head and cylinder off the motor and on the bench. Head studs in the way, want to be sure everything's square, don't want lapping paste trapped between piston and bore etc etc. I'll have to live with the oil leak in the meantime.

More work today. Apologies, no photos this time.

I did something I should have done earlier and got the timing lamp onto the ignition, checking both cylinders.

Vertical strobed in cleanly and advanced smoothly to the maximum. The horizontal didn't. The timing lamp wouldn't light at all, at any RPM. After some swapping of CDI's, checking pickup coil voltage etc, I realised that I was running the old HT leads that had come with the CA Cycleworks coils. Unscrewing these showed nasty cracks in the silicon inner insulation, on the horizontal cylinder coil end, with one or two copper strands making direct contact with the HT lead's jacket. There were no marks of any kind on the outside of the lead.

Swap old HT lead for new (the ones that came with the Ducati OEM coils) and bingo. Timing lamp strobed in cleanly and stayed with the cylinder through to full advance.

Vibration was still there, though...

First things first, was a bearing disintegrating in the engine? Checking the oil mesh filter and magnetic drain plug showed some fine powder and a couple of tiny flakes, nothing significant. I don't have to get into the motor, at least not yet. This is good news.

The AFR gauge showed me a rich mixture on the vertical cylinder (by a couple of points) and slightly richer on the horizontal cylinder (a point or so more). The plugs are suddenly coming out of the engine a lot blacker than they used to be, so probably carburettor re-tuning is the next thing to attend to if I want to smooth the running out a bit more.

While I was at checking things, I had a look at compression, screwing in a manual car gauge using a threaded adaptor. Results were 90 psi H, 95 psi V.

The gauge is pretty clearly marked green - ok - and red - issues - with both the above results well inside the red zone. Before ripping anything apart I decided to run the numbers. What (theoretically) would the cylinders return as a compression test, given that I was using a threaded adaptor which had a pretty decent amount of dead volume?

Compression gauge adaptor: 2.6 cc
Cylinder bore: 92 mm
Cylinder stroke: 68 mm
Compression ratio: 9.2
Nominal capacity: 902 cc, 451 cc per cylinder.

Compression ratio is defined as: (volume swept plus volume of combustion) / volume of combustion.

This allowed me to work out that V (combustion) is around 55 cc. So the adaptor volume (although it'll affect things) probably isn't that significant.

Then I realised that the engine features late inlet valve closing - this valve closes 60 degrees after BDC. So on low RPM intakes and compression strokes, the piston's actually pretty far up the bore again before the intake valve closes. This reduces the swept volume and the compression ratio.

The conrod (on the i.e. models, I hope it's around the same on the earlier carburetted bikes) is 130 mm long. It's a reasonably simple geometry to sketch out. Trig time. After some calculations, it turned out that volume swept after that intake valve closes is 360 cc, not the nominal 451 cc.

This reduces CR to 7.55, at least during starting while gas flow is slow enough that cylinder over-filling etc won't be significant.

So... if 1 atm pressure is 14.7 psi, 14.7 psi x 7.55 CR = 110 psi.

This is still in the red zone on the gauge markings, with the green only completely taking over from the red at 120+. This 110 psi is a theoretically perfect compression result from a healthy cylinder at low enough RPM that gas flow effects don't come into things. If the 60 degress ABDC valve isn't taken into account, the expected compression pressure would be 14.7 psi x 9.2 CR = 135 psi.

This could be achieved, you'd just have to spin the motor pretty fast to do it. In the meantime I'm happy with the 90 to 95 psi measured. I still have the oil leak, but I know I'm not getting rough running from bad compression on one cylinder.

[OddDuck]

Back into it... I went for a test ride and finally decided that it's early failure of the main crank bearings. Vibration was linked directly to engine RPM. It didn't correspond to engine loading, tested by feathering the clutch but maintaining RPM while rolling. I will have to get back into the cases after all.

The bike uses an unusual main bearing scheme, at least compared to Japanese bikes: it's got roller element ball bearing mains, opposed taper, with preload onto the crankshaft via the cases. There isn't supposed to be any free axial or radial movement whatever.

Symptoms: vibration when running despite good fuelling and good ignition. Initially noticeable but OK, gets worse as the motor warms up. Gets better again if the bike is parked up briefly, rapidly goes back to what it was. It's steadily getting worse ride by ride too.

I think the variation once parked and cooled is due to differential thermal contraction, cases versus crankshaft. If the engine's been warmed up (ie with a warm crankshaft) but then is shut down, the cases will cool first. They'll contract a wee bit onto the crankshaft, restoring some of the preload, or at least taking up some of the open clearance.

Anyway, back to the big work... pull motor, split motor. To do this, the sequence is:

Fairings off
Exhaust system off
Carburettors off
Rider footpegs off, rear brake caliper too
All engine wiring loom disconnected
All hoses, wires etc cable tied to frame freed up
Starter motor cable disconnected
Rear shock removed
Battery and fuel tank removed
Engine stand plates fitted and bike positioned directly under lifting point.

Then frame bolts (just two) undone and frame lifted off and walked aside with one hand on a clip-on and the other on the rear frame rail. It would have helped greatly to have had two people for this, but I was able to do it alone, just.

The swingarm removal needs some snap ring pliers - circlip pliers just won't work here. Once done, it's very easy to pull the swingarm axle and bag the shims.

The lifting straps are just my standard ferry tie downs. The manufacturer points out very clearly that they aren't rated for lifting, but 4 x 250 kg straps used on an engine like this should be OK. Tilt (if needed) can be done by slackening straps while the engine is standing on the 2x4's at ground level. Taking time, checking everything prior to the actual lift, lifting in stages etc was done. The engine stand plates would be guillotines or shear blades in the event of a drop.

[OddDuck]

Confirmation - it's worn out main bearings, or at least, they've gone loose.

The engine supports the crankshaft at four points: the two mains, a bushing on the oil pump cover, and a ball bearing on the alternator cover. To quickly check play in the mains, I had to take both covers off. This could be done with the engine still in the frame.

It was possible to push the crankshaft by hand - I measured around 0.5mm to 0.6mm of free play. It was disconcerting to see how much the flywheel would move if I pushed it. It looks like the main drive gears provided some support on the oil pump side of the engine - the gear teeth still look OK, at least by eye.

As far as why this has happened:

Non-Ducati main bearings
Pre-ignition and increased pressure on crankshaft etc
Too much initial preload
Too little initial preload
Pre-ignition, overheated engine cases, and too little preload leading to rolling element skidding and premature wear of the races
Permanent flex and set of the engine cases
Cracking of the engine cases around the bearings
Cracking of the crankshaft
etc etc, maybe it's better to stop thinking now

I really don't know. Could be any of these reasons, could be any combination too. Only way to be sure is to separate the halves and check everything. The clutch is pictured because it had some oil coming out of that compartment, but that's a very minor issue for later.

[T.W.R]

Get some DPI to check the gears for stress cracks :yes:

[SVboy]

The saga continues......

[OddDuck]

SVBoy: Yeah, saga would be about the right word!! Perfect riding weather too.

TWR: thanks - have found this:

http://tradetools.co.nz/products/2845550

Unless you have another recommendation?

[Voltaire]

I fell your pain, my BMW R90/S is still under a blanket after doing a top end rebuild and finding the RCA on the top end failure was no oil getting to rockers.

Quick flick thru your thread. Main Bearings SKF 72 (3)07 BEP?

I put that in a search with Ducati and only your thread comes up.

Tends to suggest no one has gone down this route before.

BMW have at least one BMW only bearing in their gear boxes, use generic at your peril.

People have used bearings that don't have enough clearance on them too, ends badly.

I'm not saying the ones you used are incorrect but some things IMHO are better sticking with OEM and engine/gearbox

internals are one of them.

Put the bike under a blanket, ride something else and enjoy the Summer.

Facebook is reminding me of " this time last year" just prior to the BMW shitting itself in Timaru.

[T.W.R]

TWR: thanks - have found this:

http://tradetools.co.nz/products/2845550

Unless you have another recommendation?

CRC 3109 is what a couple of the engineers used at work, same sort of 3pack item like the Rocol and about the same price.

You could probably take the bits you want to check into your local engineering shop and they'd do it for you while you wait for a fraction of the cost of buying
some that you would only use a portion of and turn it to a shelf ornament.

[OddDuck]

Tonight's effort (no pics sorry) was getting heads, barrels and pistons off in preparation for the casing split. Hopefully that's tomorrow. That's been covered in detail earlier, just a couple of things to say really... first, the workshop manual doesn't mention the gravel. Splitting the cases means that anything falling inside can be removed again easily but if it was just heads / barrels type work, you'd really want to avoid this happening.

The engine's more than a bit of a gravel trap. The stuff gets caught in fins, in the little gulleys that Ducati have thoughtfully engineered at the base of both cylinders, around belt covers etc. The engine stand's useful here, it's possible to put the relevant section of the motor upside down and then have at the gravel with pick / screwdriver / scrubbing brush etc. Gravity takes the gravel down and away from the motor. I wouldn't treat a nice new paint job this way though, it'd be strictly degreaser and light scrubbing with a paintbrush, also upside down or sideways if possible.

Second, it's going much faster the second time around. Most of the gear's here. I have made mistakes with my orders, though. Going through the exploded parts diagrams and picking out replacement bits by eye and memory isn't as good as a systematic approach, line by line ticking off of parts. Anything that's a seal, gasket, O-ring, or bend tab washer should get replaced. I've just found another such washer tonight that I don't yet have on order. Damn.

TWR: thanks, good advice.

Voltaire: Thanks mate. Yep, chancing it with non-Ducati main bearings was a bit dicey after all. They did work for around 12,000 miles, I wouldn't do it twice though... I've got the proper Ducati-supplied RHP bearings this time.

RHP 7207X2

RHP 7307X2ETN

I'd love to go bike shopping but have an issue with space, can't fit 2 bikes + car in garage and after car thefts in my street (my last car was one) there's no way I'm street parking my car at night any more. I've dabbled with the idea of an ST3 or ST4S. The 900SS is about a month away though, I just have to stay the course.

Facebook reminders... aargh

[OddDuck]

TWR - have purchased a 3-piece kit of the CRC Weldcheck 3109 stuff you'd mentioned - was in Twigg's buying a 46mm spanner and it was right there so why not.

Today's effort - splitting the cases and getting the crankshaft out.

The bearing puller was needed for getting the spacer sleeve off the shaft that carries the clutch hub. I'd notched this last time with a Dremel for exactly this operation. There's nothing to grip to otherwise.

The primary drive gear nut was an eye opener. This was torqued properly on assembly; it was only just more than finger-tight when I took it off today. The safety washer's there for good reason. The M6 and M8 cap screws holding the gearchange selector arm mechanism were dangerously easy to undo as well.

The nut holding the generator hub and flywheel on hadn't loosened at all. If anything it might have tightened. This was a rattlegun job to remove.

The 46mm spanner (got a 15" crescent in the end) was for counter-torquing the proper primary drive gear puller, which I'd bought a couple of weeks earlier. The puller is not cheap but worked like a charm, there were none of the dramas and delays that I had with the first pull while using a standard beam-and-leg 10-ton puller.

I noticed scoring on the oil supply end of the crankshaft - it looks like the shaft has been getting supported by the bushing pressed into the pump casing, since the main bearings weren't doing the job properly any more.

It feels like the shell bearings on the crankshaft journal are OK. There's minimal lateral play side-to-side on either conrod small end, and for now I'm going to call them as undamaged instead of disturbing the cap bolts to examine surfaces and take measurements.

With the casing split and the crankshaft out, I found something unexpected: only one main bearing seems to have failed, this the slightly smaller one on the alternator side. The photo doesn't show it clearly, but when the bearing came off the crankshaft, a lot of caked-on grey gunge was found over the spacing shims, the inner shoulder of the crankshaft, over the bearing inner race, etc etc... it was everywhere. In contrast the transmission side bearing is super clean.

Taking a closer look at the obviously damaged bearing showed occasional pits and spalling (if that's the right word for bits of the raceway surface where a flake has come off?) but this was hard to photograph. It wasn't the hammered, indented surface I was vaguely expecting, but I think that getting a clear view would involve breaking up the race cage and disassembling the bearing.

The oil gallery plug on the crankshaft itself has loosened, again. There are the beginnings of score marks on it, where it's been running on the bearing. I'm not sure what I can do about this aside from using loctite again.

[OddDuck]

I tried checking load ratings for the SKF bearings vs the RHP's... Curious as to why I've had an early failure. No definite numbers so far aside from angular contact angle.

Normal ball bearings have a contact angle of 0 degrees.
The RHP's are at 15 degrees.
The SKF's are running the more common angular contact angle of 40 degrees.

All else being equal - materials used, number and diameter of balls, raceway surface etc - the contact angle will be the biggest difference in the radial loading that the bearing can carry. The angle will be all about trading axial loading for radial loading.

Running some numbers and trigonometry, if F is the maximum force that can be applied through that contact angle before trouble:

40 degrees: allowable axial loading is 0.64 F, radial is 0.77 F

15 degrees: allowable axial is 0.26 F, radial is now 0.97 F

That's assuming a lot. The contact surface area used, raceway to ball to next raceway, will have a huge influence on load capacity, to name just one variable. But looking at the angle alone, if 0.97 F (on the normal 15 deg. bearing) could be considered 100% of the necessary radial load capacity, going to a 40 degree bearing means a drop in load capacity of

100 - (0.77 / 0.97) = 21% reduction

If the original design ran the bearings close to their raceway loading limit then this drop in capacity could be enough to go above the limit, even in an engine running properly. I've had bizarre ignition problems. It's anyone's guess just what's been getting shoved through the crankshaft. No wonder the SKF's didn't make it.

So yeah, I have to agree with Voltaire - even if it's not obvious at first, there's good reason to stay OEM when rebuilding. Not all angular contact bearings are the same.

[OddDuck]

Right, might have something useful for someone out there. DIY crankcase bake oven.

Simply chuck your case half into a cardboard box, wrap up the top with the box flaps / towel etc, and heat via hot air gun aimed inside through an open corner. Control is via kitchen digital thermometer, stuck through the cardboard. Works a treat, surprisingly.

It's actually better than a domestic oven in terms of warmup time and stability. It's also a lot more tolerant of used motor oil and dirt etc, you don't have to do exhaustive degreasing first.

The reason I was doing this was the bearing support cups. I had to get the transmission side one out and since the cylinder head studs are still in, the case halves don't fit into the oven any more.

Ducati use a steel cup pressed into the crankcase halves to support the main bearings. It's actually a pretty good idea I think - the cup is a very fine sliding fit on the bearing at any temperature, so bearing changes are possible quickly and easily, in theory at least. You don't have to heat cases, it's a careful pull and you're done.

The alternator side bearing change went without a hitch. The transmission side was another story, with much messing around with a bearing refusing to seat and a bearing cup apparently distorting, and finally I heated the case half and drove the replacement bearing and then the cup itself out to check components against damage properly.

The bearing cup has fractured. It looks like someone has taken a can opener to it. There's no way that this can be trusted to support a preload on the crankshaft main bearing, and it's possible that this cup has been this way for some time. There's a mark on the outer face of the cup where I think it's popped out of the casing and been rubbing on the transmission gear.

It's subtle. This actually looked OK while in the casing, it took a lot of messing around trying to get the bearing to seat before I twigged that something was wrong. The fracture is inside a groove, down in used engine oil etc and mostly closed - it is not obvious by eye. Long and short of it, if you've had a main bearing failure, I'd strongly recommend driving out the bearing cups for on-bench inspection instead of taking them on trust.

I had a think about the likely cause overnight and reckon there are two parts to this failure:

1) Ducati designed the cup with an internal groove at the base, to guarantee that the bearing end face sits flat and true. This groove has thinned out the cup wall, making the part weaker... the groove is standard practice when seating bearings and presumably is also there because the cup had to be ground to size to get such a fine tolerance. Grinding wheels don't tend to do sharp end radii very well, so the end of the diameter had to be undercut to finish it properly.

2) It's very possible that the cup was fractured during assembly by someone who fitted the bearing to the cup, then drove the whole lot home in one go. The bearing would have transmitted the push to the base of the cup. I think the correct sequence for this part is to drive the empty cup home, pushing from the top surface only, and fitting the bearing itself afterwards.

So it's now necessary for me to make up a specific push tool, my set of bearing drivers don't quite go to this diameter.

Stein Dinse order placed, 2 to 8 week wait on replacement parts. Voltaire, your advice is starting to sound pretty good right now.

[AllanB]

I like the hot box idea. A degree of risk the cardboard may start smoking?

Mrs B was unhappy this weekend at the smell coming from the oven as I cured heat resistant paint ............. :niceone:

[OddDuck]

Ta - 100 C was OK, I took care to direct the hot air into open space at the center of the box. So far the cardboard is looking a little dried out but that's about it.

Might be an idea to put the box on a concrete floor and well away from anything else though, I really should have thought of what I'd do if it started going wrong :)

[OddDuck]

Parts orders from Stein Dinse arrived last night. I'll be rebuilding the bike over the next couple of weeks.

It's been a fairly involved few weeks prior to this. With the bike possibly laid up right throughout summer I've been out looking for a second ride. I'd had the bright idea that I could go shopping with $5K-ish and get something basic, run that for a few months, then get the 900SS running again and move the second bike on. Treat the inevitable loss at sale as cheaper than renting and just ride, etc etc. I had this idea before I had any real experience of the current market.

Buying a second old bike which then broke down would have been a disaster. Cash is tight, legwork is cheap in bucks if not in time, it's cheaper to go looking at other bikes now than to fix this bike right here in front of me later, etc etc... it pays big time to be fussy at the front end while shopping. There's a lot of traps for the unwary out there. Let's just say that it's been an education. No wonder people get motorbikes brand new.

I've spent lots of hours looking at ads, getting out to see bikes in the real world has been a bit slower but much more valuable in terms of learning.

Bikes looked at so far: Honda VTR1000F (x2), Ducati ST2 (the Turner's job), Ducati ST4S. The Hondas just felt cheap (and both had serious issues), the ST2 felt perfect but didn't go, and the ST4S was a cautionary tale. This latter bike looked mint in the photos, OK in person, but turned out to have a twisted up front end during the test ride. It had been crashed. The handling had been destroyed. The engine was an absolute beast. I felt like Wile. E. Coyote riding his Acme rocket while chasing the Roadrunner... it's all fine until a wall comes along...

Anyway, I'm still shopping. The last six months have made it clear that it's a good idea to have a reserve bike and I'm appreciating now why serious riders either run brand new or have a stable. Or both, bucks permitting. Currently the first choice is an ST2 (not the higher powered 3 or 4 valver's) but I'll have to actually ride one to be sure.

[SVboy]

Was one of the VTRs TM listing. 1483862992? If so, could you PM me with what you found was wrong?

[OddDuck]

PM sent. BTW thanks Voltaire!

Carrying on, getting the new bearing cups into the cases... transmission side first. I used the hot box idea again, this time using a wristwatch to give a decent soak time of 10 minutes at just over 100 C.

I spent a while prepping for this five minute job, getting everything lined up... pulling the case dowels was really something that I should have done earlier. I don't want these getting caught on a bit of support 4x2 during the cup drive and maybe causing a problem with an engine case. Ezi-outs and a spot of CRC get the dowels straight out. There were no issues driving the replacement bearing cup in.

I didn't photograph this but I reckon that Ducati have updated the cup design. The new cups don't have the internal runout groove. I'm not sure how they're made (very high class CNC turning perhaps?) but it's a beautiful smooth internal wall, a fine base radius and then the internal flat. It's clearly much stronger than the old design.

Initially I'd been thinking about just leaving the original alternator side bearing cup in place - if it ain't broke, don't fix it - but after seeing this it might be a very good idea to replace this cup as well.

Wiping the gasket surface was done this time with a folded over rag and a good wipe with the brew (1 part isopropyl alcohol to 2 parts white spirits), this and some scrubbing seemed to work pretty well. Strongly suggest mechanic's gloves if anyone out there is going to start using this stuff.

[OddDuck]

Bits on the side... cleaning the swingarm, hugger and chain up before refitting. I can get all these onto the bench before refitting so why not.

It was water based degreaser for the swingarm and paintbrush / kitchen sponge plus bucket of water. I used kerosene and a paintbrush for the chain, with the bit being scrubbed semi-immersed in a parts tray. I haven't re-lubricated the chain yet, I should do this soon or else there's a risk of tearing the O-rings the next time the chain is flexed.

Cleaning everything up means that cracks, chewed up fasteners etc become apparent. The bit of semi-flexible plastic that guides the chain and protects the swingarm is cracked, I'll have to get this on order for replacement at some later time. The welds on the swingarm are fine, just shadowed in the photo.

Something I've been quite keen on for this rebuild is plain English labels on all the parts. Ducati don't put more than a part number onto the bag. Fine... if I'm in the garage and it's late at night, I really don't want to go through the exploded parts diagrams if I can help it. Much easier to bag and label when parts arrive.

The attached PDF is something I'm keen on trying for setting the preload on the main bearings. I think it's much simpler and more reliable than the method followed earlier from the Haynes manual. If you can't see it, it's a simple idea: assemble crankshaft into gasketed cases, leaving some open end float. Use a dial gauge or similar to assess the end float, zeroing the gauge and then lifting the crankshaft. The total shimming is then whatever the measured end float is plus 0.3 mm. Divide this shimming by 2 and you've got the shim stack needed on each side.

[OddDuck]

Tonight's effort: modify the engine stand / lift plates so that I've got a base for the dial gauge. I wanted these plates as close as possible to the four shafts which need shimming measurements. Since I'm doing the crankshaft, it makes sense to check the others and change shims out if necessary.

The photos make it look like the required screw holes were drilled in close proximity to the engine, maybe even using the casings as drill guides... nope. I marked out with a scriber and then got the engine well out of the way and covered it up before the power drill came out. Drilling was steel plate on bench with bits of 4x2 underneath, ruled and centerpunched drill positions, nothing fancy. Then I cleaned the workbench and the plates. I really don't need metal shavings caught in my case bearings.

The drill holes themselves were chamfered and then sanded as well, just to be certain. It'd be all too easy to have steel burrings carve up the gasket surfaces on the engine cases.

It's not possible to check all four shim clearances on one side: crankshaft, shift drum, input shaft, output shaft. I've ended up sorting out a plate for each side of the engine. There's going to be a fair bit of putting stuff on, taking stuff off, flipping the block, etc. It is heavy but it is possible for one reasonably strong person to do this on the bench.

[OddDuck]

Got the other bearing cup changed out. It was a hassle but in the end I was glad I did it... by eye, it looks like there's a crack in the groove, the same as the other side but not as advanced. If I'd left it I'd have had another failure. The photos show the old (polished) and new (black) cups and their grooves. I've tried to show the crack but the lens won't quite go that close. It's probably worthwhile trying the CRC Weldcheck stuff on it, just to have a play.

Having managed to borrow a dial indicator and a stand, I spent some time yesterday shimming the crankshaft and checking end float in the gearbox shafts and shift drum.

To my mind, this is the way to do this. It's a good way of taking a complex measurement and making it simple.

It does involve a fair amount of physical work and patience - the cases get turned over or split and re-joined a few times - and patience is needed for each measurement too. There was a fair bit of jigging of bits to get the dial indicator into position and rigid enough to be trustworthy.

I found out in the week that there are two kinds of dial: gauge and indicator. One's a lever (gauge), complete with corrections for angular deviation, and the other is a plunger (indicator). Either can be used for this kind of work but the indicator / plunger type is the most convenient.

The Ducati specification for 0.3mm preload turned out to be way too tight, in the end. That's purely my own opinion and going by feel: the bearings felt like they were grinding, on any motion of the crankshaft. Not good. A quick note here: if memory serves, the advice given in the Haynes manual is even tighter, 0.4mm preload, and if I did that last time around then that might be the reason for the bearing cup failure. A lot of force goes through those bearings with the motor running and failure by fatigue will happen at much lower stresses than sudden, catastrophic failure immediately after assembly... I'd get a few months down the road and then I'd be splitting the engine cases again.

I don't want to split the engine cases again. Time to get this one right.

I checked discussion of preload figures and found, courtesy of our American friends at ducati.ms, that 0.15mm is widely quoted. Further checking found a very interesting result: one of the guys did a controlled bake of his assembled engine cases, up to liquid-cooled and then air-cooled operating temperatures, and he found that 0.15 mm preload gave him 0.05 mm free play at air-cooled operating temperature. He was happy with that and full credit to him, I hope it's worked out. My own belief is that opposed contact bearings like these need some preload to maintain ball-to-raceway contact, at all operating temperatures. Without this there's the risk of the balls floating or skidding, leading to a rapid wear condition.

I ran my own calculation, simple linear thermal expansion of aluminium cases versus steel / iron crankshaft over a length of 100 mm and a temperature rise of 130 degrees (final operating temperature 150 C) and found an expansion of around 0.15mm. I've decided to go with 0.20 mm preload, making sure that there's still forced contact at normal operating temperature. This will settle with wear, of course.

An unwelcome surprise was end float on the gear shafts and shift drum: I'd thought I'd got this right the last time around... guess what, either the tolerance stacking or taking measurements over long distances with the verniers not quite at 90 degrees got me. They're all out of whack.

Shift drum: 0.15 mm end float (probably OK)
Output shaft: 0.15mm end float (outside the 0.10mm spec)
Input shaft: 0.03mm end float (way inside the 0.10mm spec)

The input shaft is a worry because the cylindrical roller bearing on one end doesn't really have the capacity to deal with axial loading. If that shaft warms up faster than the cases then it could go to a loaded condition. I'll have to open the cases again and sort out these shims before proceeding further.

[BMWST?]

any idea why the turners st2 didnt go??Were they up front about it not being a runner ?

[OddDuck]

any idea why the turners st2 didnt go??Were they up front about it not being a runner ?

Just left there, selling on hope? I guess it was running when it was dropped off, then non-bike people being left in charge of it possibly didn't put the battery onto a tender. I certainly didn't see one when I walked in.

Seller never got back to me about uplifting the bike from Turners and getting it running. Maybe he was reading my other thread.

[OddDuck]

First go using the CRC Weldcheck stuff.

Pretty simple stuff to use but it looks like it takes a bit of experience to get reliable results... I can't say that it worked particularly well for me. Some hassle, delays, and a shitload of really nasty fumes. In future I think I'll be doing a total immersion in the isopropyl / white spirits brew, scrubbing with a paintbrush and then going over the surfaces with a high-mag optic. Certainly it was a pain to clean up complex surfaces like gear teeth.

Anyway, here's the results. As far as I can tell, no cracks found in either component (despite my earlier comment about the bearing cup), any red lines are due to my pretty lacklustre rag wipe-down prior to development. The main drive gear looks fine after all. I want to re-check the bearing cup, though.

[BMWST?]

............................................ Maybe he was reading my other thread.

If he was he could see it couldnt go to a better home:)

[OddDuck]

Today's effort: getting the cases back together and then rebuilding the rest of the engine's bottom end. I've now got the clutch and alternator covers back on.

A very quick play with shims this morning sorted out the gearbox input shaft, now running with 0.085 mm free play. There weren't available shims to tighten up the clearances on the output shaft due to parts no longer available, although next time I'll check the situation with the same year 900 Monster, which uses the same engine. I'd sorted the parts issue in this way with the timing shaft gear lock washer.

Not really all that much to say here except that bagging and plain english labelling everything paid off. Prior experience really paid off. The engine stand and a second table to work off were very helpful.

[OddDuck]

If he was he could see it couldnt go to a better home:)

Awww thanks mate

[T.W.R]

First go using the CRC Weldcheck stuff.

Pretty simple stuff to use but it looks like it takes a bit of experience to get reliable results... I can't say that it worked particularly well for me. Some hassle, delays, and a shitload of really nasty fumes. In future I think I'll be doing a total immersion in the isopropyl / white spirits brew, scrubbing with a paintbrush and then going over the surfaces with a high-mag optic. Certainly it was a pain to clean up complex surfaces like gear teeth.

Anyway, here's the results. As far as I can tell, no cracks found in either component (despite my earlier comment about the bearing cup), any red lines are due to my pretty lacklustre rag wipe-down prior to development. The main drive gear looks fine after all. I want to re-check the bearing cup, though.


The techs at work use a black light once they've done the treatment, any cracks literally glow :msn-wink:

[OddDuck]

Today I realised that I've made a mistake and need to get the cases apart again. Dammit.

It's one of those situations where either it's a bit tough now or it's a lot tough later... going back in means losing around ten to twelve hours of work. Not getting this right means losing about sixty, plus waiting time for parts.

As to what went wrong... a couple of things, really. I misread the dial gauge. It wasn't 0.550 mm, it was 0.520 mm (see photos; I lifted the crankshaft with a screwdriver for the second one). The other one was that I did some back of an envelope arithmetic wrong. I divided 1.72mm by 2 and got 0.76 mm.

Oops. Big oops. It's 0.86 mm. There goes my 0.20mm preload, right there.

This happened because I was rushed, stressed, tired, pissed off, and didn't have a calculator to hand because it was the garage and who keeps a calculator in their garage. Going to have to change that.

A few other thoughts have occurred, while kicking myself. There are a few gotchas in this very important measurement.

Gasket.
New bearings, and what they're lubricated with.
Casing flex under contact.

The gasket is important for this measurement, for two reasons: it crushes between the cases, then it swells again once it gets oiled.

Some rough measurements from tonight, a brand new gasket which has never been used versus the old gasket rescued from the bin:

New gasket: 325 microns thickness
Old gasket, between cases, near screws: 315 microns
Old gasket, between cases, equidistant between screws: 365 microns
Old gasket, open space in sump with no compression: 385 microns

So it's pretty clear that oil makes the gasket swell up. Maybe the old gasket wasn't the same as the new gasket, but the trend is clear. One thing I can say is that the casing half bolts were damn tight, when I undid them earlier. The threads weren't clogged with ash.

Bearing lubricant: the stuff coating new bearings is thicker and stickier than engine oil. It has to be, it shouldn't evaporate off the bearing or allow damage during shipping. The issue here is that this stuff is part of the shimming measurement too. It'll get rinsed with engine oil once in use, so that lubricant boundary layer will change. Maybe the lubricant layer isn't more than a few microns difference, maybe it is significant after all. I do know that preload is quoted differently for re-used bearings than it is for brand new.

Casing flex: the measurement is directly affected by how hard the operator presses the crankshaft against the upper casing half during this measurement. The casing will act like a spring. There might not be more in it than, say, 5 microns, but the effect is there.

The one thing I can be reasonably sure of is the thermal expansion. The casings will run at around 120 C. That means I need at least 150 microns of preload, just to keep up with the differential expansion between casings and crankshaft.

Fun and games, fun and games. The casings have got to come apart again and I've got to re-run the free play measurement, now that the new gasket's had crush, oil and time. Maybe it's worthwhile washing the new bearings with clean engine oil too. The new target preload figure is 170 to 180 microns.

TWR - thanks for the info - at this stage I'll leave the crack testing, but it's good to know.

[pete376403]

Do you really think the factory would take 20-30 microns into consideration when banging an engine together? Could they really take the time to select the parts (or have a range of parts with that variation for selective assemble) and still be able to sell the bike at a competitive price?

[BMWST?]

Do you really think the factory would take 20-30 microns into consideration when banging an engine together? Could they really take the time to select the parts (or have a range of parts with that variation for selective assemble) and still be able to sell the bike at a competitive price?
maybe there is preliminary work done to optimize batches

[OddDuck]

Do you really think the factory would take 20-30 microns into consideration when banging an engine together? Could they really take the time to select the parts (or have a range of parts with that variation for selective assemble) and still be able to sell the bike at a competitive price?

(prior post edited because it was too long, too detailed and too speculative - the 20-30 micron thing is a reference to possible gasket crush during assembly and measurement, then swelling during service, thus decreasing bearing preload by 20 to 30 microns)

Hell, no. Not a chance. 50 to 80 microns would be about as good as you could hope for. This is Ducati after all. The engine designer / assembly procedure writer might take it into account though.

What I'm on about is that I think there's a couple of subtleties to what's going on. If you're being fussy (I am and make no apologies for it) then an effect with 20 to 30 microns is interesting, if there's a couple of effects like that and they add up then I reckon it's worthwhile understanding it properly. Put it this way, if I get this wrong then sooner rather than later I'll be stuck with a bike off the road again.

As to getting product out the door and making a buck... no way are they assembling cases, checking clearances, taking everything apart and fussing with shims, then reassembling and checking everything again, turning a heavy case assembly over on a bench. Nope. It'll be a coordinate measuring rig linked to a computer program that tells the assembly guy which shims to use. About five minutes on the machine and maybe ten assembly and that'll be it, done and out the door.

[OddDuck]

Stripping the engine down again is a weekend job - there's a lot of spreading out of parts etc, it's best done when there's six to eight hours available in a row. I've spent the week addressing the need to sort out the surfaces on the spigots sealing cylinder barrels to heads.

First thing: measure what's going on, on the cylinder head at least. I haven't looked at barrels yet.

I used a depth micrometer for this, finding (to my surprise) that there actually wasn't much variation. Going around clock marks on the spigot, everything was around 2.95-ish millimeters depth. Maybe plus 10 microns, maybe minus the same amount. The obviously damaged surfaces didn't measure as having been gouged any deeper. It's possible that the micrometer simply measured the remaining high spots, thus giving an optimistic reading.

Ok, so I tried fitting the cylinder barrel to the head. It didn't sit flat, it was possible to rock the thing back and forth, ever so slightly. Right. Should have been perfectly flat. Something's been banana'd, can't rebuild like this again.

The first thing I tried was Kickaha's suggestion of directly lapping barrels to heads. I got about ten minutes into this before I decided that it wasn't working well for me.

A few reasons...

Most of the lapping pastes around are meant to lap hardened steel alloy valves into whatever material valve seats are made from. They're not really meant for cutting aluminium. I'm sure someone somewhere does these aluminium pastes, it's just that I've never seen them. Anyway, the paste I had (cheap, generic engine work stuff - Powerbilt, billed as fine grade, 320 grit? - was simply too aggressive. I was getting nasty dig-in marks carved into head or barrel.

The cylinder head doesn't rotate freely around the barrel. There's a clash between the timing belt gate and where the exhaust header is mounted. There's only a very limited range of rotation - around 15 degrees or so - which just isn't enough to get the surfaces to properly match.

The spigots are different diameters. The barrel (external) is smaller than the head (internal) by about half a millimeter, which of course it has to be. These shouldn't jam together after being used. This means that surfaces could be lapped in one place, but fitted together in another, thus spoiling the matching between them. This joint has to be as close to perfect as possible, regardless of assembly variations. Flat going onto flat will do it, something that needs repeat positioning down to a few tens of microns won't.

I tried using an orbital motion instead a simple rotation, then various rotations at different centers, combinations of orbital and twist etc, then finally quit before I damaged anything too much. It's clear that a dedicated tool of some kind would give a better result, so that's the next step.

[OddDuck]

Next step: design and make the tool.

A trick I've used a lot over the years is to use wet'n'dry on flat blocks. It's not perfect but it's dependable, in terms of reasonably flat finishing of workpieces.

My idea was to lathe up a cylinder which would fit into a cylinder head. There'd be a sheet of wet'n'dry secured against its face and I'd simply press and turn the thing to cut the spigot flat and clean again.

I had a couple of mis-steps, making the tool... it turns out that decent slabs of aluminium plate can be hard to obtain at short notice. I tried buying a cheap cast iron barbell weight, with a view to machining that to size. Nope. I hadn't realised that cheap cast iron tends to case harden during the casting process. It is not easy stuff to work with once this happens.

In the end the tool was made from a harmonic balancer, a glorified belt pulley off the end of a V6 car engine crankshaft. There are a few similar scrapyard items it could have been machined down from. Anything with a big enough diameter and enough perimeter rigidity would do. I wanted a central core to press down on, though. Pressing on the outer rim would introduce distortions, so anything with a big hole in its center was out.

The other part of the tool was a cylinder guide. I want to fit the same tool to the cylinder barrels, have it remain centered, and turn and cut the cylinder spigots too. The black disc in the photo is a piece of turned ABS plastic for this purpose, it's meant to bolt to the tool and secure the wet'n'dry at the same time.

I used double-sided tape to carry the wet'n'dry for the cylinder head work. Final trimming of the paper to the tool diameter was done with knife edge running against the edge of the tool itself. I tried trimming with scissors and very quickly decided that I was just going to destroy these; the grit from the paper gets between the blades very easily.

The tool fits and turns in cylinder heads as it should, I ran the first cuts tonight. I haven't tried working on a barrel yet. Note the use of engine oil, buttered onto the paper prior to making any cuts - it's both a cutting fluid and also a keeper. I don't want loose bits of silicon carbide dropping through the cylinder once the engine is reassembled.

[OddDuck]

And results... the magnifying glass makes for a cheapo macro lens.

I'm happy with results from the first cylinder head, but 800 grit paper took a while. I went around the perimeter with the depth micrometer again and found that there's been less than 10 microns taken off in this cut, without any noticeable skew in the spigot face. At the same time the cut looks reasonably flat. Possibly it's domed slightly, but I don't have the gear to measure this properly.

[OddDuck]

... by getting another ride in the meantime.

Ducati ST2.

Went up today with a mate and did the deal, sorted insurance etc and then rode the new bike home. There are a couple of issues - I used these as bargaining leverage - and I'll cover these in a new thread. Nothing that'll keep it off the road right now though :)

Good to be riding again, I was having a great time on the test ride and then getting it home.

[eldog]

Ta - 100 C was OK, I took care to direct the hot air into open space at the center of the box. So far the cardboard is looking a little dried out but that's about it.

Might be an idea to put the box on a concrete floor and well away from anything else though, I really should have thought of what I'd do if it started going wrong :)

heat and concrete don’t mix too well, don’t ask me how i know.:sweatdrop

suspect water absorbed by concrete turns to steam......

[nzspokes]

... by getting another ride in the meantime.

Ducati ST2.

Went up today with a mate and did the deal, sorted insurance etc and then rode the new bike home. There are a couple of issues - I used these as bargaining leverage - and I'll cover these in a new thread. Nothing that'll keep it off the road right now though :)

Good to be riding again, I was having a great time on the test ride and then getting it home.

Nice. Now Pro tip, dont pull both bikes apart at the same time. :lol:

[OddDuck]

Nice. Now Pro tip, dont pull both bikes apart at the same time. :lol:

Yeah, everyone I know has been saying similar... don't know why!

[SVboy]

Well done that man! If anyone deserves a riding break, it is you!

[OddDuck]

In between going a bit OCD on the new ride and sorting out general holiday stuff, I managed to get onto (finally) getting the fuel tank squared away properly. It's been sitting on the garage floor, covered with an old towel.

It was just a matter of time before something got dropped on it or I managed to clip it with the car or something equally horrible and unnecessary happened. I decanted the petrol (very slowly and painfully) via the breather hole and got the tank into a stacking, rolling plastic clip lid box, with padding via rags, towel etc.

The breather hole thing took ages. I had self-sealing fuel hose quick releases on the other other lines and it's very difficult to get in underneath a full tank on the bench anyway, that's why I didn't use those, and I completely forgot about the drain plug on the tank. I noticed this again about three-quarters of the way through the job, thought about it, but didn't want to break a perfectly good seal.

Really wish I'd gone and bought one of the fuel siphon-pump things... but in the end it might have been a bit of a blessing. There was a lot of messing around with opening the filler cap so air could get in to let fuel get out, tipping, tilting, angles, mopping up minor fuel spills, getting petrol onto my hands and washing my hands and getting gloves on like I should have done first, and of course refitting the breather valve on its stub of hose when I was done.

The little breather valve didn't quite fit into the plastic box. OK, I took it off again, not a big deal. There was a very noticeable release of pressure from the tank when I did. Right. Breather valve's probably stuffed. It is pure chance that I noticed this.

It's a funny wee beast... it's supposed to do a few things. It lets pressure out of the tank. It stops fuel from sloshing out under braking (it's at the front upper of the fuel tank). It's also supposed to let air into the tank, to balance pressure again after a while running with an open throttle. There were a few failures of this valve on the 99 - 05 Supersports, and the high-pressure fuel pump managed to suck enough of a vacuum that the fuel tanks crumpled like a beer can as a result.

The valve is easy enough to test. Pull it off the bike - it's about the most accessible component on the entire bike - fit a clean piece of new hose, and try blowing through it from each end. Mark it or photograph it first. It's directional. It'll let flow through slowly but lock up at pressure, going one way, and it'll breathe freely the other way. There's a little rubber disc inside, held by two dissimilar springs, which acts as a valve. Mine had failed earlier via swelling of the rubber, probably from unleaded fuel over time. I just haven't been checking it.

As to why this is significant... I'd been having a lot of ongoing problems with carburettion and tuning, particularly a weird leaning-out effect while under sustained running.

I've spent ages thinking that the lean-out issue was thermal. I haven't been thinking about things like fuel delivery or liquid level in the carburettor bowls.

If this valve has jammed, then that directly affects delivery pressure to the fuel pump and thus the carburettor bowls. It wouldn't have to be a full jam to do it either. If air flow into the fuel tank doesn't keep up with fuel use then that could cause this.

If there's an issue with the carburettor floats or needle valves then that could do this too. The needle valves use spring plungers (against vibration) and it's possible that these springs introduce a proportional effect into fuel level versus required delivery volume to the bowls.

Another possibility is the fuel filter. I have never changed this. It's a pretty good bet that it's been ignored by a succession of owners. If the bike's running, why worry about it... filter clogging is gradual and would show up the most at high fuel demand.

The last possibility is the hosing and hose clips inside the tank itself. If there's something loose or perforated then I could be losing supply pressure there.

Anyway... they're all one hell of a lot easier to investigate and fix than installing dedicated temperature control. Simple things first.

[OddDuck]

Lapping the second cylinder head - this time it's the horizontal head.

This went very much as for the first, with a couple of differences. The head's a lot more warped, requiring more cutting with a rougher grade of paper, and the area where I think oil was leaking from has different features to the fretting damage I've seen on both heads.

The fretting follows diameters, as per the vertical head, with the worst area being by the exhaust port. The leakage paths (there are several of them in parallel close together) are radial, and look like grit has been cutting lines into the spigot's sealing face. I'm not sure of the mechanism for how the grit moves, but it took quite a while to cut the paths away with the paper.

I've stopped with a bit of the fretting damage still present. This is diminishing returns work and I'm OK with reassembling with it like this.

[OddDuck]

Lapping the cylinder spigots.

The guide disc was spaced outward from the paper with a couple of M8 flat washers. This was to try to avoid getting grit between the guide and the Alusil coating used inside the cylinder, although in the end this might not have been such a big issue. The guide is deliberately too thin to contact the cylinder at the top ring mark, if any damage occurs it will happen in an area that never sees contact during normal use anyway.

That said, I was still very careful with grit and oil moving from cutting face to the bore. Every time the lap was lifted off, I was careful to oil the paper (if needed), but to wipe the spigot itself down. This was to avoid carrying any grit into the bore when the lap and guide were refitted for the next stage of the cut.

The paper was buttered with oil every time there was a paper change. Silicone carbide is very hard but also very brittle and bits fall off the paper every time it gets flexed or worked... I didn't want loose particles falling into cylinder bores and sticking to the walls.

Initially I tried lapping with the lap on the bench and the cylinder inverted above it. The idea here was that excess oil would flow down and away. It didn't work, the cylinder tended to vibrate and chatter, even moving it by hand. In the end the lapping was done with the tool on top and the cylinder on the bench, as per the heads.

[OddDuck]

Things weren't quite so good with the horizontal cylinder... it's cracked across the spigot, close by the exhaust valve. The last photo is a crop of IMG_1392, with the hairline crack centered in the frame. I simply wouldn't have seen this without having cleaned the surface up and possibly it's been flying under the radar for some time. As far as I can tell, the crack runs down to the flat, machined surface under the spigot and stops there. I can't tell how far it goes inside the cylinder. The Alusil coating and the cylinder's wear and tear makes it confusing to try to track the fracture.

I think this has happened because of all the issues with the ignition and pre-fire during the compression stroke. This would have been putting huge strain on the cylinder, particularly with the piston near TDC. At the time of the highest pressure, the spigot is the part of the cylinder carrying the strain. It's also the thinnest part of the cylinder, there's only so much outer diameter available.

I'm going to gamble that the crack isn't going to either leak oil or get worse. If I can get the fuelling sorted out so that the bike doesn't run lean and hot, and with the ignition now sorted out, it might hold up as it is.

[OddDuck]

Stripping the engine case assembly back again for the crankshaft re-shimming, time to get back onto it. Oil evaporates, humidity moves in, I don't want to put this aside to find a rusty engine in a month or two. A few bits and bobs...

There's a pair of M4 cap screws holding the front sprocket's locking tab washer on. These are supposed to be loctited on with 222 and can be a pain to remove with the engine in this state - there's no compression to use as a countertorque, not with cylinders and pistons off. An oil filter wrench worked on a clean sprocket.

I deliberately didn't close the locking tab washers up flush to the entire relevant face of the securing nut. Each end was left curved and open. This was so that it was possible to get a screwdriver blade in later without having to chisel-tap the washer open. I don't want to put hammer-driven shock loads through bearings if I'm going to re-use them.

On a similar note, I've marked out the position of the locking tab, visible even once the nut's on again. It should be possible to bend the washer anywhere to lock it, but I'd prefer to avoid the tab to shaft area of the washer for this.

The timing gear (large) was a nightmare to remove earlier - there's almost but not quite enough room to get the legs of a gear puller onto it. Screwdrivers don't quite go in. A pair of allen keys can be sneaked into the holes and then levered against each other to bell-crank lever the gear off the shaft.

Removing loctite... I wanted a clean, properly locked reassembly. Old loctite either cracks and starts dropping into places it shouldn't go, or very efficiently wipes the new liquid loctite off when the screw threads are done up again. Best to have as close to bare, lightly oiled metal as possible. The use of a thread gauge as a scraper was probably a bit brutal (on the gauge) but I want to take loctite off, not metal. Chasing rolled threads with a button die can cut into the threads, weakening them.

It was a similar story with the M8 x 1.25 tap used to clean the clutch basket mounting threads, in the larger transmission gear. This time it wasn't loctite so much as accumulated engine ash. There was quite a bit of wiping with cotton buds, CRC 5.56, and then the 2:1 white spirits / isopropyl alcohol mixture afterwards. I had to wash the bearings out with the CRC, it's very hard to avoid ash moving around during this process.

[OddDuck]

I was surprised and disturbed to see what looks like corrosion damage to the clutch pressure plate. It looks like clutch dust has built up between this and the first steel disc. Either the dust has packed and then hammered dents into the pressure plate, or a galvanic corrosion pair has formed between aluminium pressure plate and steel disc. Possibly both, I can see both what look like burnished dents and also much rougher, jagged pits.

I've cleaned it up but sanding it out will take far longer than it's worth. The pressure plates aren't a particularly expensive component anyway. The more expensive anodised plates wouldn't have this problem.

Of passing interest... the clutch was locked up. Lightly, at least. This persisted even with the springs removed. It looks like the friction material will bond to the steels, given a period of sitting around.

Today has ended with the cases still together but everything else out of the engine, bagged and labelled.

[OddDuck]

Main bearings reshimmed, finally. This time I'm happy with the preload, I've gone for 0.18 mm. The crankshaft turns with some interference, as described in the workshop manual.

The gasket I've been working with so far, brand new, never fired up, has been stuffed by repeated refits. A few areas around the screw holes have become stretched and gone conical instead of flat. This is a problem, the last thing I need is distortions or wrinkles.

When I'd placed the parts order I'd ordered two gaskets, they were cheap enough and it was basic insurance. That decision has paid off. Ducati don't use enough locating bushes between the half cases and unless the mechanic is very careful with the gasket placement then misalignment and gasket damage is almost inevitable.

Didn't want this to happen again with the spare. The pin punch was used to feel where the gasket was placed and then adjust, if necessary - it's possible to use the nose of the punch to pick up the paper lip and then give it a sideways tweak, with the half-case above it lifted to allow movement. The case bolts and screws should go into their threads without any interference with the gasket.

I'd gone ahead and purchased my own dial gauge and stand, via Trade Tools:

http://tradetools.co.nz/products/4900120

For some reason the stand and gauge sets are buried in the micrometer section of the site, it took some scouting to find these.

I'd been worried about the resolution, hysteresis and accuracy of the 10 micron gauge but in the end it turned out to be perfectly appropriate for this level of work. I checked again with the 1 micron gauge from earlier and all this showed was that too much resolution can actually be a bad thing, it's possible to start chasing ghosts.

Crankshaft lifting was done with the main gear pin wrench, this turned out to be near perfect for this simple job. I'd gone and purchased a cheapo calculator for my shimming calculations, getting it wrong once was enough.

[pete376403]

No engine that I have worked on with vertically split cases (so, old Brits, slightly less old Jap trailies, English and Czech speedway motors and most recently my 08 KLR) has used a gasket between the halves. Even the old Matchless G50 didn't leak between the case halves (just everywhere else). Putting a gasket there seems like its just asking for trouble, adding a whole bunch of variables to what should be a fixed measurement. italians, eh?

[OddDuck]

Interesting. Ducati actually went away from gaskets a while ago and use sealant instead, probably to avoid crush / swelling issues as you say.

I prefer the PTFE-impregnated gaskets though, I find them a bit easier to work with in terms of cleaning up cases.

[OddDuck]

Going back into the pump case, to make certain the main drive gear was sitting on the crankshaft properly.

I'd been finding that this gear came off the tapered shaft very easily. The nut goes on with 107 to 117 Nm torque; it was loosening with about half this, then the gear would pull off the taper with maybe 20 Nm applied to the puller nut. Both of those are just by feel, I was using a breaker bar, but it was definitely lighter to take off than it had been to put on. It's supposed to be a beast to get off.

My experience with tapers has been that they go together easy but come apart again with difficulty. If otherwise, something's up. This is the main drive gear, it's transmitting nearly all of the engine's torque and power. It's an expensive component, mounted on a very expensive crankshaft, sitting in pricey and hard to get engine cases. Don't really want problems with this, especially since a consequence of failure could be an engine lockup while riding a corner or at speed.

It took about an hour to get in again, most of that comprising taking the clutch apart. I ended up being very glad I did. It turned out that the gear was sitting on the key, torqued up against the key's flat outer face on one side and the tapered shaft on the other. The bright raised ridge of metal on the key itself is where the key has been getting cut, while being jammed into its own keyway.

The Loctite 510 used to lock and seal the clutch basket screws has a habit of fragmenting and falling into the engine while the bolts are being withdrawn. Not a problem while the engine is in its normal orientation, bits and pieces will go down, end up in the sump and get filtered out. While it's on its flank, as pictured, bits of crumbly Loctite can fall into the gearbox input shaft's bearing races. This can be cleaned up with a cotton bud and some pushing around of the bearing, just don't force the thing through a jam. Use the range of motion available and lift fragments out of the bearing races.

The cut on the key itself is pictured. I've put a rag around the crankshaft main bearing, I didn't want anything falling into this during work.

[OddDuck]

Having a look at the key itself.

I took a file to the burr and removed this, then tried refitting the key and the main gear. Not much joy, something was still wrong.

I got vernier calipers onto both the key and the keyway, finding them very close in length but apparently still passable. The key kept refusing to go neatly into the slot machined into the crankshaft, though. It took a bit of close looking to see why, shown on the photo with the mirror.

The length matches fine. The corner radii on the key don't, so it jams into place. It goes in just far enough that it looks OK, but the key ends up sitting high enough to lift the main gear by the gear's keyway.

A spot of filing and using wet'n'dry and I had the key fitted into the crankshaft keyway properly - just loose enough to push home, not loose enough to rattle. The next step was to make sure that there weren't burrs or similar on the gear or the crankshaft. The edges of the keyway, on both components, were quickly radiused using a needle file and paper.

[OddDuck]

Testing for gear lift via key off the crankshaft... first check was using vernier calipers to see how far the gear was placed along the crankshaft, both with and without the key. It turned out that this does show lift, just not directly - it's not easy to measure how much height should come off the key by this method, if it's necessary to take some off.

While planing the key down in height a bit (from 5.00 mm to about 4.86 mm, on block and wet'n'dry paper, measuring via verniers) it occurred to me that what I really wanted was to look at the gap between key and gear, down the slot. Perhaps an easier and more direct method was using a bit of paper as a slim feeler gauge. This worked very well and showed a gap of at least 0.20 mm on an untightened gear. I can be certain that the main gear is now sitting on the taper, over the full surface.

I've refitted the lock washer and nut, applied clean engine oil to threads and nut face, and tightened up to torque. I haven't tested by attempting to pull the gear off again, there's a way a taper feels when it's being done up and this felt right so I've called it as done.

The base of the engine is now back together again, waiting on pistons, cylinders and heads to be refitted next.

[OddDuck]

Fitting pistons to cylinders, fitting base gaskets to engine.

The base gaskets are there to seal against oil leaks, they don't deal with gas pressure. Ducati use Loctite 510 as a sealant, that's the bright pink beads visible in the photograph. I've kept the assembly stock, with 0.4 mm gaskets used on both horizontal and vertical heads. It's possible to modify squish and marginally increase compression by omitting these gaskets or DIY'ing something out of thinner metal, but the price paid for that is vulnerability to impacting heads and pistons, if the engine has any coking due to running rich. Best restricted to race engines which are torn down frequently.

Getting the pistons into the cylinders was a bit fiddly, until I learned the trick: slightly misalign the cheap Stanley piston ring compressor's leaves. This has to be done because Ducati left a generous 45 degree chamfer on entry to the cylinder bore. The rings like to pop out of the compressor and bind up on this chamfer during the push... it'd be very easy to try to force it and break a ring, carve up the cylinder, damage a piston ring land, or some horrible combination of all three.

If it jams during assembly, just pull it, get it back into the compressor, take the time and set it up right. It'll go in once it's lined up, with those compressor leaves actually in the 45 degree chamfer but stopping short of the gentler taper leading into the main bore. Cylinder and compressor were wiped down and oiled before assembly, with ring gaps set at 120 degrees to each other in their lands, as per the workshop manual.

It's not really possible to put pistons onto conrods and then lower the barrels over them, unless some kind of split-half ring compressor is available - something that can go in past the studs and come out again between them.

[OddDuck]

Heads onto barrels.

Pretty simple really, fit whatever seals are needed, carefully fit the head square and flat onto the cylinder spigot, fit the head nuts and tighten these up in stages to full torque.

One trap with this assembly is that it's possible to torque up with the head off-square, initially at least. The feeler gauge applied between flats on the cylinder and head was an attempt to make sure I had things nipped up square before the 1-2-3 torque sequence started. The torquing in stages should normally pull things straight, but I wanted to give the process the best possible start. This actually did work, after a rough sort of fashion. The stud bolts have a fair bit of spring in them, the fresh loctite sealant squashes a bit, etc etc... but it's better than squinting and guessing.

The unusual black wrench pictured is a crows-foot, carefully ground out to a classic open-ended form. This grinding had to be done to get access for the torque wrench. With the heads overhanging the head nuts, it's not possible to take a straight shot with a traditional socket. It's also not possible to do this on a more recent engine, these use 12-point head nuts and unless a thin section 12-point crow's foot can be found, it's go looking for the very specific U-shaped spanner used for this job. Hdeusa make one at a decent price but it's payment via Paypal and probably freight via Youshop, they aren't a big outfit with a flash web sales frontage. Note that nut flanges and threads were greased prior to assembly, as per the manual.

Something I didn't photo was running a swab through the horizontal cylinder's mounting holes. These were filthy with ingested road dirt and oil, there's access to these via the gap between head and barrel once the engine's assembled and they tend to trap gunge. I didn't want the studs to push muck out of the holes and then have this drop into the cylinder bore during assembly.

[OddDuck]

Timing belts.

There are all sorts of arcance procedures and gear for setting timing belt tension. I've had success so far with the allen key as feeler gauge method, as outlined here:

http://www.ducatisuite.com/belttension.html

It can be difficult to fit the belts in the first place, though. Pulleys are supposed to be lined up with dots, but on the vertical head this happens at a point where the closing springs countertorque the camshaft. It'll want to spring back while the belt is being fitted to the pulley. The circlip pliers were being used to hold this pulley in position, they're narrow enough to drape the belt over them first.

Belt tension was done with 5mm allen key horizontal cylinder, 6 mm vertical, as per the web page. The engine was turned by hand, putting the camshaft into an unloaded position to make sure that the belt was slack on both sides, before setting tension. I'd marked belts prior to taking them off, showing cylinder and running direction.

I've made a change to the inlet manifold stud isolators. Time to see if the running rough and loud issue was thermal or electrical... the Tufnol insulators had an issue with crushing over time and needing the fasteners torqued up periodically. I've machined up some aluminium top hat washers to take their place. The manifolds will run hotter, but maybe that's desirable in terms of fuel not condensing on the manifolds during sustained running. Or maybe it's just small potatoes. The only way to be sure is to test it, once the bike's back together.

[actungbaby]

I was surprised and disturbed to see what looks like corrosion damage to the clutch pressure plate. It looks like clutch dust has built up between this and the first steel disc. Either the dust has packed and then hammered dents into the pressure plate, or a galvanic corrosion pair has formed between aluminium pressure plate and steel disc. Possibly both, I can see both what look like burnished dents and also much rougher, jagged pits.

I've cleaned it up but sanding it out will take far longer than it's worth. The pressure plates aren't a particularly expensive component anyway. The more expensive anodised plates wouldn't have this problem.

Of passing interest... the clutch was locked up. Lightly, at least. This persisted even with the springs removed. It looks like the friction material will bond to the steels, given a period of sitting around.

Today has ended with the cases still together but everything else out of the engine, bagged and labelled.

Dont drive yourself mad buddy your doing fine . you should see my cbr 900rr engine been on the bench over a year know .

I tryed that clr stuff guy recommended it for alloy carby bodys . i had rusty steel clutch plates . wife droped the bottle and lost most of it. was tiny bit so i added
so water sat the plates in and took the rust of real well . its only surface.

I have a xr 200 crank that bearings have rusted and gone through the shiny stuff so know your frustraion. ;-) .

glad your posting sorry for the butting in normal transmission ressumes .

[actungbaby]

Fitting pistons to cylinders, fitting base gaskets to engine.

The base gaskets are there to seal against oil leaks, they don't deal with gas pressure. Ducati use Loctite 510 as a sealant, that's the bright pink beads visible in the photograph. I've kept the assembly stock, with 0.4 mm gaskets used on both horizontal and vertical heads. It's possible to modify squish and marginally increase compression by omitting these gaskets or DIY'ing something out of thinner metal, but the price paid for that is vulnerability to impacting heads and pistons, if the engine has any coking due to running rich. Best restricted to race engines which are torn down frequently.

Getting the pistons into the cylinders was a bit fiddly, until I learned the trick: slightly misalign the cheap Stanley piston ring compressor's leaves. This has to be done because Ducati left a generous 45 degree chamfer on entry to the cylinder bore. The rings like to pop out of the compressor and bind up on this chamfer during the push... it'd be very easy to try to force it and break a ring, carve up the cylinder, damage a piston ring land, or some horrible combination of all three.

If it jams during assembly, just pull it, get it back into the compressor, take the time and set it up right. It'll go in once it's lined up, with those compressor leaves actually in the 45 degree chamfer but stopping short of the gentler taper leading into the main bore. Cylinder and compressor were wiped down and oiled before assembly, with ring gaps set at 120 degrees to each other in their lands, as per the workshop manual.

It's not really possible to put pistons onto conrods and then lower the barrels over them, unless some kind of split-half ring compressor is available - something that can go in past the studs and come out again between them.

Ive done with my fingers least on my xr 200 and xl 100 engines much

easier when i had my dad to hold the cyclinder for me (not anymore)
Unless he pops down from heaven.

But even with your correct gear having someone keep cyclinder level is a god send. its just getting that first top ring . going . what stag 180 % on your ring gaps. cyclinders look very cool .

[OddDuck]

Ive done with my fingers least on my xr 200 and xl 100 engines much

easier when i had my dad to hold the cyclinder for me (not anymore)
Unless he pops down from heaven.

But even with your correct gear having someone keep cyclinder level is a god send. its just getting that first top ring . going . what stag 180 % on your ring gaps. cyclinders look very cool .

Thanks! For me, with this engine, it's the oil control ring. Strange but something about the narrow edges, the second edge always catches unless it's lined up just right.

Ring gaps were set at 120 degree intervals, as per the workshop manual. That said 180 would probably work just as well.

One thing about the rebuild: I didn't worry about this on the vertical, but on the horizontal I caught the oil control ring gap lined up almost exactly on the point where the cylinder and head had an oil leak. It might have been like that before. That's the lowest part of the cylinder, having the gap there really won't help with excess oil buildup. I've rotated all of those rings 90 degrees, so now the oil control ring's gap lines up with the gudgeon pin.

[actungbaby]

Thanks! For me, with this engine, it's the oil control ring. Strange but something about the narrow edges, the second edge always catches unless it's lined up just right.

Ring gaps were set at 120 degree intervals, as per the workshop manual. That said 180 would probably work just as well.

One thing about the rebuild: I didn't worry about this on the vertical, but on the horizontal I caught the oil control ring gap lined up almost exactly on the point where the cylinder and head had an oil leak. It might have been like that before. That's the lowest part of the cylinder, having the gap there really won't help with excess oil buildup. I've rotated all of those rings 90 degrees, so now the oil control ring's gap lines up with the gudgeon pin.

i use my finger nails sure is tedious but you can do it. i never had the right gear i be using that. i whouldint be too concerned cylinder are tapered . and with heat and the compession the rings get pushed more out. in two stokes some arent completly perfectly round . so they say i dobt u notice with the eye though.

am not mechanic though . i only done one engine put toghter back in the day.

gee reminded me i try get piston down and then u panic check the rings where still 120 % i think just go for it . i love to help where are you. ?

patrick

ps the pistons are slighty oval i meant not the rings yes from memory oil rings gave me issue too.

Has the duke 3 rings oil scrapper and compression. oil more likey be forced up and any whould going down with be a design to keep crank bearings and con rod sweet.

[OddDuck]

The Ducati uses 3 rings, compression, scraper and oil control, as is the usual pattern in a 4-stroke engine.

Using fingernails to fit rings... yeah I can see that, but for me it's a 3 week wait on parts and I'd really rather not take the chance with a ring binding up and then breaking, or taking something out along with it. Tools are cheap these days, if the ring compressor costs less than one ring set then I know which way I'm going.

The cylinder bore is parallel and circular over the working stroke of the rings. It isn't like that over the full length of the bore though. From the base, there's a 45 degree chamfer, then a much more gradual taper leading in to the parallel section. It's the chamfer that's the issue. The ring edges are razor sharp after they've worn a bit and they always bite in on entry, so they've got to be snuck in past the chamfer and allowed to contact the gradual taper. After that it's OK.

Thanks for offer of help but I'll say no as politely as possible... working on this strictly solo means I can do things 100% my way, at my own pace.

[OddDuck]

Getting into the fuel tank today, pulling the old fuel filter out.

The way in is via the filler lid and the flange surrounding it. This is held in, ultimately, by a ring of grub screws engaging in a V-groove, and an O-ring. The grub screws come straight out, after all of them have been found (the heads are very small and if the flange has oxidised then they hide very well). The O-ring can jam. I had to lift the flange as far as I could, get some PB Blaster in the gap, and work the flange for a few minutes to get it out without putting a lot of force through the top of the tank.

The arrangement inside the tank is:

Mesh filter
Fuel pump
Fuel filter
Metal pipeline to petcock and carburettor supply
Metal pipeline for fuel return, terminating in an open end at nearly the highest point in the tank.

The fuel pump is held in a twin spring C-clip, the fuel filter is connected to the metal pipeline via a very short section of 8mm ID fuel hose and hose clips. It's a five minute job to undo the hose clip and then pull these out as an assembly, after having lifted the filler cap and tank flange.

[OddDuck]

Next stage: check everything.

The mesh filter is discoloured, its fitting ring is rusty, but otherwise it appears fine. No tears or holes, no obvious jamming, didn't have any issues pouring isopropyl alcohol through it during an attempt to clean it. I'll call it as probably OK, which is just as well. Stein Dinse indicate that this is a discontinued part. I've had a look at 600 / 750 engines (both Monster and Supersport) and no luck anywhere, if anyone knows a replacement pump inlet filter that'll fit, can they comment please?

The pump itself was working just fine the last time the bike was running. It's not serviceable anyway, if anything's wrong it's a total replacement.

The hoses ( 2 x 5cm lengths of 8mm ID fuel hose) have set over time but don't appear to have leaks or tears. It'd be a good idea to replace these.

The filter, though... this is quite definitely a consumable. The maintenance schedule recommends a clean / change every 3,000 miles / 5,000 km's. I haven't changed it once and I purchased the bike at 32,000 miles. It's now got 62 K on the clock. Being curious, I sawed it in half for a look. Some sediment at the base, not much... the element's clearly used though. The filter uses paper and to the eye it looks quite badly loaded up. The two photos show the filter still wet and then after it had dried out.

On reflection I really should have tried connecting a hose to it and seeing if I could blow through the thing first. I've got a brand new one to compare against. Too late now though.

While I was at it, I changed the petcock out for a replacement. The old petcock wouldn't shut off properly, which was a pain when doing any work on the carburettors. I took it apart to see why this happened and how it worked. To do that, I had to force the cap unscrewed with a pair of vice grips. The end of the valve cap has been rolled, to prevent it coming undone (under vibration while running I guess).

It's a simple design, two o-rings on two diameters. The larger O-ring controls fuel against leaking out of the base of the petcock. The smaller O-ring is the fuel on / off seal, working by insertion into a narrow, parallel bore. There's a very slight rounding off on the edges of the 90 degree entry, but there's nothing nice like a taper to guide the seal or anything. Yep, it gets guillotined every time it gets used, as shown by the damage to the seal in the photo. This petcock design really wasn't Ducati's finest moment, no wonder it wouldn't shut off properly.

I've tried to photograph what I can see of the shut-off seal in the replacement (upgraded) spare part, shown here sitting on top of the old petcock. As far as I can tell, it's a similar O-ring, but pressing against a conical face in the manner of a needle valve.

I also noticed that the hose barbs on the new petcock are slightly rounded off, they don't feature razor edges like the first one had originally. These edges cause problems with rubber shavings making their way into the carburettors if the hoses are reused, as would be normal after refitting carburettors post cleaning / adjustment.

The attachment for both designs uses a 15mm hexagonal connecting bush, featuring a LH and RH thread starting from each end and meeting in the middle. It sounds fussy but it turned out to be good to use in practice, it means it's easy to set the petcock at any desired angle and then tighten up to seal to the tank.

[OddDuck]

Reassembling the tank innards.

I found out something useful while doing this - it's a good idea to get the verniers onto every hose fitting to confirm sizes, it's also good to check hose diameters once fitted to verify that the hose clamp chosen is within its size range.

Doing this showed that Ducati have mixed and matched sizes through the tank. The pump outlet is 8mm, the filter (both ends) is 8mm, the piping used in the tank is 1/4". A close look at the old hoses (using verniers) showed that one hose was 8mm, the other was 1/4". They looked alike enough that I'd assumed they were both 8mm's, at a glance.

It's not a good idea to use 8mm fuel hose on a 6.4mm pipe. It might seal over the pipe end, where it's been rolled to form a barb, but hose should really be tight over the entire diameter, the whole way along the rubber to pipe interface. I've tried using slightly loose hoses on pipe barbs etc before and it just never works out, the slightest wrinkle or opening and there'll be leakage, no matter how tightly the hose clamp is winched up.

Post assembly, it occurs to me that the smart thing to do here is to use two bits of hose between filter and fuel tank, 8mm then 1/4", with a barb-to-barb size change adaptor and a couple of extra hose clips. Use a looped length in the hosing to get everything to fit in, if necessary. The fuel filter doesn't have to be in an exact position or orientation in order to work, just as long as it doesn't rattle or scrape too much.

As it was, I've forced a piece of 1/4" hosing onto the fuel filter, stretching the hose a little with needle nose pliers, using bearing grease and then pressing it on with the help of a socket. This very nearly broke the fuel filter, it's not particularly strongly made.

I've rebuilt using Jubilees, the more commonly available Tridons have a reputation for sharp edges and cutting into the hoses. My own experience with the Tridons (in stainless) suggests that they can come undone with time and vibration. I really don't want fuelling issues happening inside the tank, while on tour.

The cable cutting pliers turned out to be a good purchase, making things a lot easier. Previously I've been cutting hoses with a box cutter knife, it's sharp but suffers from friction bindups with the rubber while the blade is passing through. The rubber then flexes and it becomes difficult to get a clean, neat cut.

Reassembly of the tank fuelling flange was helped with some bearing grease. The weather seal gasket goes back on from outside, while slightly lifting the flange - it took a couple of goes to get this done.

The fuelling flange carries a weather drain hose. This passes right through the fuel tank. If this comes off, either at top or bottom, rain will end up dripping into the fuel tank. It's a good idea to check for blockages in this piping (it does pick up road dirt etc) and also cracks, lack of securing clips etc. It's just 8mm outer diameter, I didn't have the relevant hose clip, so have improvised for now with a 20mm length of the 8mm ID fuel hose. It's a bit bodgy but the drain hose isn't pressurised, and anyway has been holding on by itself for over a year now.

After this I took my first look at the carburettor floats in a while, I wanted to check spring tension on the needle valves. I found one tab slightly bent, with a 1mm difference in float heights. I don't know how this happened, unless I managed to force the floats upward while trying to refit the fuel bowls.

[OddDuck]

Putting the swingarm back onto the engine, putting the frame back on top. A big step towards getting the bike running again.

This needed the engine stand plates modified to take wheels. This was something I should have done as part of the initial design. Almost every item of garage lifting gear - the engine workstand, the engine crane, even the bike paddock stands - allow heavy items to be moved. Previously I'd been stuck with where the engine got lowered to. Once the motor was sitting on the plates, that was it, it didn't move again until the bike's rolling stock once more. This was annoying with the previous swingarm / rear wheel refit, since this was just close enough to the wall to be really awkward.

Enough putting up with it, time to improve it. I didn't have a choice anyway since moving the workbench meant that there wouldn't be enough room or access to do things the old way.

The roof lifting point can't be moved. The beam's the least rotten of the bunch and the only one I've bothered to reinforce, put it that way. An engine crane would have worked, but I've lent mine out at the moment and don't have room left for it in the garage anyway.

So, converting the engine stand plates into roller skates. Wheels were purchased from Rex Wheels and Castors, through bolts from M10, collars were machined down from a piece of 16mm tubing. Total cost about $100. I had to use the lathe to take the center diameters of the wheels out to match the collars, too. During this machining I found that the wheels were different diameters, I had been given 4 wheels of 98mm and four wheels of 102mm diameter. It doesn't sound like much of a big deal except I don't want axles skewing or the assembly rocking, it's worth checking these small things if you're doing similar work.

All this to roll an engine about a meter forward. It sounds like the hardest way to get a tiny job done, but now it's there for whenever I need it. The ST2 uses the same pattern engine castings as the 900SS, so I can use these stand plates on this bike as well.

The chainblock was used to get the engine down off the workstand. There were no issues whatever with the actual move, all the work was in the preparation.

[OddDuck]

A quick note for anyone else doing this exact job on a Ducati... get the swingarm sorted out before dropping the frame back on. The swingarm axle shimming and pinch bolts are much easier to sort out with the frame absent. There's no frame clutter in the way when shimming, and the swingarm can be tipped far higher than normal so there's easy access to the pinch bolts for the torque wrench.

Anyway, frame's back on. This was a much easier job with two people, one to hold the frame and the other to guide it in, getting various cables, leads and hoses out of the way while fitting it.

I'd been worried about getting the fore and aft mounting points properly lined up before fitting the long bolts. In the event, this really wasn't a problem. We put the rear bolt in, then lifted and tilted the engine by reaching in through the frame to the horizontal cylinder head, for fitting the front bolt. The engine rotated the degree or two needed by standing on the rear wheels of the engine stand plates. I was able to lift with one hand and fit the bolt with the other, it wasn't difficult.

Swingarm shimming: while going through much messing around with trying to sort out the pinch bolts with the frame on, I noticed that the swingarm was very loose from one side to the other. I'd thought I'd sorted this out previously, clearly I hadn't. Some testing with a feeler gauge showed the clearance as 0.330 mm.

At this point I realised something important: there's got to be a clearance. They can't be shimmed until they're room-temperature perfect. The engine cases will expand due to heat and nip up against the swingarm otherwise.

So, working out the clearance:

170 mm axle length
Thermal expansion coefficient for steel: 12 ppm per degree
Thermal expansion coefficient for aluminium: 23 ppm per degree
Approx swingarm axle / engine case temperature: 100 C maximum
Measurement temperature (ambient): 25 C, checked with kitchen thermometer

Differential expansion will be 23 - 12 = 11 ppm

Clearance required: 170 x 0.000011 x (100 C - 25 C) = 0.14 mm

This is assuming that the swingarm axle warms up at the same rate as the engine. It won't; in practice it'll lag behind, possibly also being cooling through conduction via the swingarm. The worst case is then a hot engine but a near ambient swingarm axle, meaning a clearance of 0.28 mm would be more appropriate. Due to limitations with available shims, I've ended up with a clearance of 0.205 mm or so.

Some sliding of the axle back and forth, dropping shim stacks in and out on both sides etc, sorted it out. Aligning shims with a screwdriver through the hole and rocking the swingarm gently back and forth helped.

This clearance isn't mentioned in the official workshop manual and I suspect what usually happens is that people get this clearance to as near to zero as possible at ambient, with some free rotation clearance left. Then the cases force the swingarm slightly wider on the axle during the first engine run, then it stays like that until the next stripdown. I can't see this being a problem unless strain is introduced on swingarm welds or the pinch affects suspension action.

[OddDuck]

Fitting oil hoses to the oil cooler. This involved (finally) using the -6AN fittings I'd ordered in earlier.

I tried a few hose layouts before I was happy, then marked to length with a piece of masking tape and cut the hoses. I used a hacksaw with a 32tpi blade but a jeweller's saw with a 00 or similar blade would probably be the best for this - the hose reinforcement wires tend to snag on saw teeth if they can. Fine toothed saws or cut off wheels are the way to go here. The tape helped to keep the woven jacket in some sort of order, although it did fluff up a bit once the tape was peeled off.

I was careful to swab rubber dust and steel shavings out of the hose with an oiled cotton bud afterwards, I really don't want either of these getting into the engine's big end bearing shells.

Assembly of the new hose fitting was straightforward. Push hose into fitting end cap (vise helpful here), mark hose position with another piece of tape, screw fitting into end cap and hose itself, then check tape position to make sure that the hose hasn't been pushed out during this process.

It's a good system. There's no crimp ferrule or any need for them, the threaded portion of the fitting screws into the hose rubber and retains directly via the thread. The fittings themselves can be unscrewed from an existing hose and swapped or changed as needed, if the threaded portion in center is cross-compatible.

Unfortunately it looks like my Improved Racing hoses and the VPW Australia fittings aren't cross compatible though. The threads on the VPW's are 14mm, the Improved Racing fittings are 15mm. Given that the -6AN system has dimensional rules, I'm not sure why this has happened. It's not that big a deal, I can just pull the relevant end cap off and reassemble from the cut hose end, but it is surprising.

I've assembled so that the nylon hoses have the maximum possible clearance from the exhaust header, but this is almost certain to change. The Improved Racing 45 degree connector has a loose swivel seal, and I'm not sure how the fairings will fit over the hoses yet. I'd like to secure the hoses via clips at the old oil cooler mounting points, I'll probably need standoffs of some kind for this.

I've recently stumbled across these guys:

http://www.fpp.co.nz/

I'd ordered the VPW's via Trademe but FPP might be a better first port of call in future.

[OddDuck]

I've lathed up some standoffs, to go in place of the old rubber vibration mounts that carried the oil cooler in its original position. Some pipe P clips and that's it, hoses and oil cooler now secured. The photo shows an obvious oil spill in the fairing, this is from the cylinder head oil leak earlier - with everything I haven't got around to scrubbing the fairings up properly.

Fuel tank refitted, fairings and seat back on, and I'm good for the WOF check. Damn, it's good to see the old girl back together again.

[OddDuck]

Yep, back into the engine again. I'm not quite happy with how it's been running post rebuild, and guess what, I'd failed to examine or replace the conrod big end bearings.

Oops.

That's about thirty hours of work which I could have avoided if I'd just taken an extra night or two and gotten into the crankshaft / conrod assembly.

As to why it happened, it was late in the rebuild, I was getting fed up with doing this stuff as well as very tired, and my mate was onto me constantly about when we'd go riding again. I let these things make a decision for me. Engines need their details done right, and how I am doesn't really come into that. Next time, if in doubt, I'm taking the night / week / month off, then coming back to it.

The other issue is that post rebuild, and installation of nifty fuel hose disconnects plus inline secondary filter, the bike's gone from bad to worse with running lean under any kind of throttle and load. A quick run up the Wainui hill saw the AFR readings go from their usual awful 16 - 17-ish to clear off the gauge at 18+. It should be 14, plus / minus 1.

That's really bad news. Ultralean running will very rapidly trash engine components like valves, cylinder heads, barrels and pistons. I'm reasonably sure that the major reason the horizontal cylinder has a crack in its spigot is sustained lean running.

What I haven't been able to do, at least so far, is sort out what's going on and why with the bike's carburettion. It's always had issues running. I've tried almost everything to tune the carburettors and sort the ignition out. Valve timing and compression have been attended to as well, plus exhaust header sealing and inlet manifold vacuum leaks. None of it has sorted the issue out.

For a long time I was thinking I'd have to get a selection of slide needles and play with taper angles, then somehow I bumped across an idea I should have had a play with much earlier: the carburettor float height directly affects the fuel mixture, and is dependent on both baseline (static) height setting and also fuel supply pressure.

If the fuel pressure is changing, so is the float height. More pressure means more force needed to close the needle valve, so the float height will increase. Less pressure means the opposite, the floats will need less force to close and therefore will sit lower.

Carburettors are very sensitive to fuel level in the float bowls. It doesn't take much of a height change to affect the air-fuel mixture proportions. It's very difficult to see what's happening with float height while riding the bike, of course. This could have been going on for years and I'd never know it.

The behaviour that happens, again and again, is that I get the bike out of a 50 kph zone and into a 100 area. The AFR gauge ticks down from a healthy ratio to a lean ratio, over roughly 30 seconds or so. This happens no matter what I've been doing with main air jets, main fuel jets, needle position etc. About the only carburettion possibility I haven't tried is going to a more tapered needle, but these are hard to obtain.

I've been thinking that this has to be thermal, but it's also consistent with a float bowl draining to a low level and then holding there.

Then there's the very real possibility that with all the junk I've installed along the fuel lines, the fuel pump is having problems delivering enough fuel volume at any pressure to keep up with demand anyway... the brief run over the Wainui hill would seem to confirm this.

The lesson to all this is that if you want to tune your carburettors, the very first thing that should be done is to ensure that at all throttle settings, you've got consistent fuel line supply pressure (at the carburettors) and also enough supply volume at that pressure to keep up with fuel flowrate demands.

I'll hopefully be getting into this later. For now, it's sorting the engine. In a way it's kind of a good thing I went back in, I've already found a couple of mistakes with the base cylinder gaskets. I've used too much Loctite 510 on the horizontal, leading to smear gunking up and blocking an oil return line, and it looks like somehow I managed to completely forget to use any at all on the upper face of the vertical cylinder's base gasket.

There's discolouration over the conrods, too. I think the reddish colouration at the big ends is that nasty steel-on-steel contact at high pressure, similar to what I've been seeing on the chain sprocket splines on the ST2. The brownish colouration on the vertical piston's conrod, well, not sure. Maybe bad combustion from the ignition issues discussed earlier, but I really can't be sure.

[OddDuck]

Well, here's the crankshaft / conrod assembly, in bits... right, this was worth doing after all. It's been getting hammered.

Scoring is visible on the crankshaft main journal. It's centered at BDC on both pistons and running between 1/4 to 1/2 the circumference. It isn't that deep or over the full contact area, but it didn't look like this the last time I had this apart.

The big end bearing shells themselves are showing quite significant loss of bearing metal, with what looks like original turning marks in the substrate metal showing through the remaining bearing surface. The flanks of the shells are marked, showing that angles of contact have been changing, too.

Something I should have realised earlier was that loose main bearings, with off-center torque through the transmission which changes direction because it's one cylinder and then the other, will mean that the crankshaft is changing angle relative to the conrods. It'll be rattling a bit while the engine runs. It might very slight, but this means that a bearing surface which should be parallel will start being angled. This will stuff the big end bearings in very short order, since they're dependent on oil float to keep the bearing surfaces separated from physical contact.

This angling might explain the steel-on-steel contact between conrods, too. Some wear marks on the flat, parallel faces were visible, on close examination.

As a side note, I finally noticed that the conrods and end caps are stamped with numbers. If parts are disarrayed on a bench, it's possible to match them up again using this.

[pete376403]

Oil supply / flow / pressure / filter problems? Have you plastigauged the bearing clearances?

[OddDuck]

Oil supply / flow / pressure / filter problems? Have you plastigauged the bearing clearances?

No, no issues with the oil pump. I think this is a casualty of the main bearing failure earlier. The crankshaft was loose and side flex took out the half-bearings.

Plastigauge on order for reassembly work, hasn't arrived yet.

[OddDuck]

Cleaning up the crankshaft bearing journal was done relatively quickly with strips of 1000-grit wet-n-dry and CRC. I deliberately didn't go for a mirror finish.

The reason for that was a lot of chatter from American engine builders about surface finish, RA, and boundary layers in the oil film between crankshaft journal and bearing shell. Most of these guys talk about hand-finishing with 600 grit and leaving things there. Certainly after I was done the scoring was greatly improved, and if it's managed to run on the scoring without gross damage then this should work.

Fluid boundary layers are critical with journal bearings. There has to be fluid 'grab' on both sides, journal and shell, so that there's turbulent swirling between them and thus the journal effect can build up. Too finely finished might be too slippy and thus lose this boundary layer. Of course I could be completely wrong and find the crankshaft and shells get destroyed in short order once the motor fires up - aargh - but the crankshaft itself is now on borrowed time anyway... more about this below.

Regrinding crankshaft journals (what has to be done when things get really bad) turned out to be really involved. Not only is a weird-looking dedicated rig used (looks like a giant lathe, with an equally oversized beltsander) but the crankshaft itself might have to undergo post grinding heat treatment, including nitriding. Grind direction is important due to micro-somethings in the cast iron matrix leaving directional sharp edges. Fillet radii are critically important, if they're too sharp then the shaft can crack in use. And so on, there's a book's worth of similar considerations to take into account about this stuff.

In the meantime it's possible to get wrecker's parts with half or even quarter the mileage off Trademe or Ebay...

A mate told me to check the conrods against having gone out-of-round, with shells removed. I did this via transfer gauge and micrometer, finding no issues with either rod. I wasn't able to check parallelism, unfortunately. At this stage I'm not sure how the home worker could do this properly, since a pair of ultra precise diameter shafts are needed for the procedure discussed in the workshop manual.

I had a look at measuring journal clearance using micrometers as well. It turned out that there were a couple of non-Plastiguage techniques:

1) use micrometers, measure crank journal, bearing shell thickness, and conrod big end inner diameter.
2) use a transfer bore dial gauge, measure crank journal, zero the dial gauge on this reading and then transfer the gauge to the assembled conrod, thus reading the clearance directly.

There's a trick for using a drill bit shank to measure the bearing shell thickness, as photographed. I found that it had a distressing tendency to mark the bearing material and it's fiddly, no matter how careful I was.

Anyway, method 1 had problems with tolerance stacking. The plus / minuses rapidly add up to the point where the measurement is just too fuzzy to be trusted. Method 2 involves purchasing another pricey piece of gear which would get used about once every couple of years at most. It'd make sense if I was building engines all day every day, though.

As to the crankshaft itself being on borrowed time: I noticed, later during engine reassembly, that there seemed to be a bright line on the transmission side main bearing shoulder. A close look showed that it's been getting worn down, and measurement confirmed it.

The alternator side is running with a clearance of 10 microns between crankshaft and bearing inner race. On the transmission side, it's 30. This side of the crankshaft sees nearly all of the output torque and power, so it's highly loaded. The crankshaft has been rolling in ever-so-fine orbits inside the bearing's inner race and getting very slowly ground down.

The clearance is too fine for a shim. About the only fix is Loctite 641, and then it'll never come apart again, at least not without ruining that main bearing.

[OddDuck]

The idea behind Plastigauge is simple enough: it's a wax strip of a known cross sectional area. Squash it between two faces and although the width / height will change, the cross section won't. This means it's possible to infer the height (ie bearing clearance) from the width, using the handy scale printed on the fold of paper that the wax strip is sold in.

I got this off STA Parts, who delivered in about 36 hours from placement of order. Each 30 cm strip costs the princely sum of $4 or thereabouts.

I used this three times. First, with the worn bearing shells, both to learn how to use the stuff and to see what the old clearances now looked like. Second, with new Ducati bearing shells, in a red / blue combination, as I'd read recommended on another forum. Finally, with red / red bearing shells, as I'd built it last time.

Some notes from the experience...

Get some silicone oil onto metal surfaces as a releasing agent, prior to use. I had an old can of CRC 808 Silicone and this worked well enough. Engine oil didn't, and bare metal certainly ended up with waxy Plastigauge stuck fast. It took quite a bit of scraping with rags and fingernails to get it off the crankshaft journal, the first time around. There would have been no rescuing a nice new bearing shell if this had happened. The bearing metal's too soft to scrape it clean. I think I'd read somewhere that the wax will dissolve in engine oil, but I really wouldn't want this stuff interfering with a bearing's operation during startup and initial bedding-in.

The gauge itself is much more a yes / no type of measurement than anything giving clear numbers. It's possible to say that it's under X but over Y. That's about it. This is actually OK for this kind of work though. The numbers on the Plastigauge scale line up nicely with Ducati's quoted tolerance band limits. I'm not sure if that's luck or design but it's very handy.

It's important to be careful to not crush it any further while removing components, too. Obviously this would ruin the measurement, but it can be difficult to do. The conrod caps use guide pins and things can jam up.

The results were quite telling. Ducati's tolerance limits for the conrod bearing clearances are 0.024 to 0.051 mm, ie 24 to 51 microns.

Both of the old sets of bearing shells were outside spec, coming in at something between 51 and 76 microns.
The red-red shell combination was just on the limits of the spec, coming in at 51 microns or just over (or as near as I could tell).
The red-blue shell combination was a match, coming in somewhere midway between 25 and 51 microns. This confirms the advice given in the Ducati ST2 manual, by the way. I know it's a different bike but it does use a lot of the same components. There's a table of A and B crankshafts and conrods, with suggested bearing shell combinations for these.

Engine reassembly has started. I haven't worried too much about photos, having covered this earlier, but at time of writing progress is:

Crankshaft / conrod assembly done, with assembly lube and fresh conrod cap bolts
Case halves back together
Pump and transmission flank done
Alternator, starter and gearchange flank done
Vertical cylinder piston, barrel and head refitted

I'm quite keen to get this done in a reasonable time and then move on to sorting out the fuelling.

[OddDuck]

Carrying on... the engine's back together, as previous. Today was about lowering the engine from the stand and then carrying out major assembly of frame, engine and swingarm so that the bike's rolling stock again.

The photos say most of it. Previously I've replaced frame onto engine by hand - it's always been a pig of a job if working alone. On my own, it's been a desperate juggle. Cables always find a way to snag on something or get in the way while trying to fit frame to engine, then as soon as I try to fit a bolt, the handlebars will flop to one side or the other and then the frame will tip. Doing this job single-handed always ends up being about getting a bolt through and engaged, while trying to hold the frame steady with one hand. Somehow. I've managed it on the few occasions I've had to, but it has got pretty sweary at times.

Obviously with helpers this'd get a lot easier. However it can be difficult sometimes to get help... for anyone else out there just trying to get this job done, I'd found my tiedown set worked pretty well to lift, lower, and stabilise the bike. It was a real luxury being able to methodically clear cables etc as the fit was made. Keeping the bike steering locked at center using a couple more tie-downs also helped greatly.

The photo of the tie-down on its own shows a technique for doing controlled lowering. Just pressing the release button might let it explosively release. Looping the free strap back through the eyelet makes a rough block and pulley arrangement, with lots of friction controlled braking, and it becomes very easy to slowly let it down.

I'd also found earlier that it paid to fit the swingarm to the engine and torque the swingarm pinch bolts first, before major reassembly. The reason for this is that the pinch bolts can't be got at with a torque wrench while the swingarm is at a normal angle, part of the engine cases blocks access for a straight shot at the fastener.

Cue dramas with swingarm axle shims, while doing this. It seemed to have suddenly lost 0.4mm of width, until I realised that this particular assembly has to be done with the rear wheel fitted and torqued up. Pulling the rear leaves of the swingarm inwards as the axle is nipped up will open the front leaves up, and so properly running shim clearances have to be set in this condition. I left 0.205 to 0.276 mm clearance, as discussed earlier (the engine cases will expand once the engine is at normal operating temperature).

The big bits of the reassembly are done, there's a bit of fiddly messing about with cables and hoses, plus the exhaust system has to go back on, but that's it for things mechanical for now.

[OddDuck]

I've had the chance to take a look at Ducati's fuel supply arrangement to the carburettors.

The basic layout is:

Mesh filter and pickup at base of tank, fuel pump, proper fuel filter, metal piping inside tank to petcock, hose to Y joint. The Y joint then branches, with the center line going to the carburettors and the other leg of the Y returning to the fuel tank. The return piping runs to the highest and most central point in the tank before discharging into free air within the tank, above the fuel surface. The tank has a breather valve of course.

At first glance, it's a simple way of ensuring consistent fuel supply to the carburettors. Back pressure on the return line due to height should ensure consistent supply to the carburettors, even as the fuel level in the tank drops. The top legs of the Y are a high-speed flow circuit, with the carburettors sipping fuel from the center.

Unfortunately it appears that things aren't that simple... there's more than pressure due to height involved. There's back pressure due to flow resistance as well. The flow resistance is going to depend on flow velocity.

This flow velocity, even in the main supply / bypass line, will change. The carburettors will take only a little fuel at idle, but they'll want more as the throttles open. That change in carburettor demand will come out of the flow in the return line. That in turn will affect the back pressure in that return line from the Y joint onwards. That back pressure pushing fuel back to the tank is the same pressure supplying fuel to the carburettors.

As mentioned earlier, change in fuel pressure will affect the needle valves, the float height, the fuel level in the bowls and thus the fuel-air mixture strength.

I took an evening and made some measurements of internal tank piping, the Y joint itself, and fuel hoses - length and diameter for everything. I also checked the fuel pump's petrol flowrate per minute. Then I calculated (for a theoretical 900cc engine) expected fuel demands for perfect 14:1 operation.

Measurements:

Internal tank piping: roughly 5mm ID, 300 mm length on the return pipe
Fuel hose: 6.0 mm ID, 540 mm length on both Y branches
Fuel hose from Y to carburettors: 6.0 mm ID, 340 mm length
Y joint: 4.5mm ID all legs, branches 30 mm, center leg 34 mm length
H, height between outlet of discharge pipe and carburettor needle valves: roughly 300 mm
Fuel pump volume: roughly 1 litre in 38 seconds, flowrate affected by height of outlet
Carburettor demand: varies between 10 mL per minute to maybe as much as 300 mL per minute

So the first concern - that the fuel pump isn't keeping up with demand - is satisfied. The pump is delivering over 5 times the maximum expected flowrate, so that isn't a problem.

The second concern was that varying flowrate to the carburettors, via the 340 mm length of fuel hose, was causing enough varying pressure drop to affect supply at the needle valve seat. Similar to below, I calculated flow resistance at 300 mL / minute to be just 4 mm of height drop. There is an effect but it isn't more than 1% variation. A 6 mm ID fuel hose is plenty.

As a side note, a purely gravity fed carburettor arrangement will have similar behaviour to this. Flowrate in the line will cause a supply pressure drop, but it'll be minor compared to pressure head variations due to the tank emptying. On this bike, if it was purely a gravity fed arrangement via petcock at the base of the tank, I'd get roughly 40% variation. That's simply because the carburettors aren't all that far below the tank.

I then had a first shot at calculating back pressure in the return line due to flow resistance, using Reynold's numbers, tabulated values for petrol specific gravity and viscosity, and formulae for pipe flow resistance from an old mechanics of fluids textbook. It got complicated fast, unfortunately, but here's the gist of it:

Pressure due to height = fluid density x height x g (acceleration due to gravity)

Reynold's number Re = flow velocity x pipe diameter / kinematic viscosity

f, friction factor, depends on Re and tube roughness and can be found from experimentally derived charts

Height pressure required to drive flow = ( 4 x f x length of tube / diameter ) x (velocity^2 / 2g)

Any obstacle in the flow, like a pipe expansion / contraction, sharp edge, bend, abrupt edge etc will also introduce some sort of velocity squared flow resistance, but for now I've neglected these.

Anyway... what I worked out is that the pressure supplied to the carburettors via this arrangement won't be very high. Less than 1 psi, if I can trust my numbers. The other key finding is that small variations in flow velocity lead to large variations in back pressure, due to the velocity squared term.

I'd also found this page during the week:

http://members.iinet.net.au/~petercusack/aigor/TechTips/contents/CARB/dellorto/dellorto_3_2.html

The key point I took from it was that the needle valve seat had to be matched to expected flow and expected supply pressure. I found I was running 2.0 mm seats, with 190 main jets; these seats may be too small for such a low supply pressure.

The other thing I found was that the variation in pressure due to variation in flowrates isn't trivial. Running the numbers showed that, even with as little as 300 mL being taken from a 1.58 L flow, a variation in back pressure of 18% occurs. This 18% variation includes the fixed contribution from height.

This is purely for flow resistance in the above lengths of 6 mm tubing and 5 mm piping. I haven't included any terms for the Y joint, the contraction area where tube goes over pipe, bends in the piping inside the tank, etc etc. These terms will make the variation worse, everything with a flow velocity squared term in it - like in-line filters, quick disconnects etc - will add to this variation.

I have no idea of the relationship between supply pressure and fuel-air ratio for my setup, but suspect it's complicated and non-linear. What I do know is that after installing the pictured hardware on the fuel lines, my fuelling problems became much worse. It worked badly with smooth lines, it has worked much worse with clutter in the way.

I think it's real. The fuel supply design is flawed.

What I'm not sure about is the fix, I'll have to take some time to think this through properly.

[pete376403]

Being a Ducati, of course they made a complicated solution to a simple problem. Why not a header tank (within the fuel tank, at the highest point, just a simple weir, nothing special. The pump supplies fuel to that and any surplus flows over the weir and back to the main part of the tank. The fuel petcock is supplied from the header tank and the carbs are supplied from the petcock. Constant pressure from the header regardless of the level in the main tank. Everything else, line sizes, float valve sizes etc are determined by maximum demand as you have calculated.

[HenryDorsetCase]

I have a stupid question.

On the crank there are two brass slothead screws. Are they something to do with the counterweights or are they blanking a drilling for (say) an oilway?

[OddDuck]

Being a Ducati, of course they made a complicated solution to a simple problem. Why not a header tank (within the fuel tank, at the highest point, just a simple weir, nothing special. The pump supplies fuel to that and any surplus flows over the weir and back to the main part of the tank. The fuel petcock is supplied from the header tank and the carbs are supplied from the petcock. Constant pressure from the header regardless of the level in the main tank. Everything else, line sizes, float valve sizes etc are determined by maximum demand as you have calculated.

Yep I like it. Should be possible to build into the existing tank setup without hacking / welding anything, I'll have to fabricate a couple of components though.

[OddDuck]

I have a stupid question.

On the crank there are two brass slothead screws. Are they something to do with the counterweights or are they blanking a drilling for (say) an oilway?

That isn't a stupid question at all. They're oilway blanks. I've never attempted to remove them, after finding that they were good and tight during the first engine stripdown. After all this time, chances are very high that they're firmly locked into place with engine ash and any attempt to remove will break the heads.

[Ocean1]

I have no idea of the relationship between supply pressure and fuel-air ratio for my setup, but suspect it's complicated and non-linear. What I do know is that after installing the pictured hardware on the fuel lines, my fuelling problems became much worse. It worked badly with smooth lines, it has worked much worse with clutter in the way.

I think it's real. The fuel supply design is flawed.

What I'm not sure about is the fix, I'll have to take some time to think this through properly.

I admire your dedication to the scientific method. If you look you'll find flow value data for commercially made valves and fittings using the unit Cv. (Or Kv for if you're picky). You can also find flow values expressed in terms of equivalent pipe length in diameter units, which makes for easy calculation.

Or, having discovered your system is too small you could simply double it's capacity by going from 1/4" to 3/8" tube and fittings.

[Ocean1]

Being a Ducati, of course they made a complicated solution to a simple problem. Why not a header tank (within the fuel tank, at the highest point, just a simple weir, nothing special. The pump supplies fuel to that and any surplus flows over the weir and back to the main part of the tank. The fuel petcock is supplied from the header tank and the carbs are supplied from the petcock. Constant pressure from the header regardless of the level in the main tank. Everything else, line sizes, float valve sizes etc are determined by maximum demand as you have calculated.

If the lines and fittings are correctly sized you don't need the header tank, if the lines and fittings are undersized a header tank won't help.

[BMWST?]

If the lines and fittings are correctly sized you don't need the header tank, if the lines and fittings are undersized a header tank won't help.
but wont a header tank remove the fuel supply pressure variations ? A header tank will always have say 200 mm of "head"...wont vary (much)

[Ocean1]

but wont a header tank remove the fuel supply pressure variations ? A header tank will always have say 200 mm of "head"...wont vary (much)

No, the extra volume in a tank adds nothing to the pressure compared to the existing tube. What's causing the problem is the flow restriction downstream from that, and at the very low pressure involved it doesn't take much to restrict the flow. I once organised a clear pvc tube return line up through the steering head and into the fuel cap, just like a normal vent tube. It meant I could see immediately if the pressure dropped at all, you could see the petrol level drop back down the tube.

There are systems that contradict almost every sensible design improvement you can think of, but they mostly involve weird fluids at much higher pressures. I recall one project where doubling the pressure produced almost twice the flow, doubling it again stopped it literally stone cold dead. General rule of thumb, though is doubling the line diameter gives 4 times the flow, at the same pressure.

Which reminds me of a Smokey Unick story. His response to the new, rigorously enforced fuel tank capacity limits was to increase the size of the fuel line to the engine, to about 2".

[eldog]

Tell me if I am wrong, because this is a long shot

apart from general wear and tear, your main problem that you believe you have now is running lean.
from your description this doesn’t occur when you go for a test ride apart from going up/down hills or spirited riding.

your calculation for amount of fuel required, is this for steady state? I ask this as I know someone who has a fuel rate meter on their dash, it’s acceleration which causes this to go min 3-5x more than highway (100kph) running fuel supply rate.

I am suspicious about the return line not being below the fuel level at all times. I wondered if the pump is unable to supply the instantaneous amount of fuel, fuel is then sucked down the line along with air. If this goes for too long air will enter the carb via the return line.

I would be keen to run a transparent hose from the Y to the tank to watch the fuel level.

Everything system I have worked with, always uses the path of least resistance, air, oil, heat etc.

i would also apply soapy water in case of vacuum/airleaks etc.

like those off-road bikes with the fuel hose through the cap.

you have been very thorough and the explanations/photos are excellent so even a dummy like me can understand:Punk:

Ocean1 - ya beat me to it with a much simpler explanation

[OddDuck]

Tell me if I am wrong, because this is a long shot

apart from general wear and tear, your main problem that you believe you have now is running lean.
from your description this doesn’t occur when you go for a test ride apart from going up/down hills or spirited riding.

OK, maybe I should have been more clear... yep, it happens all the time. Even cruising. Open that throttle up and the bike leans out, no matter what I tune the carburettors to. Then it riches up at idle. About all I've ever managed to do is shift the point where it runs properly, at about 14:1. This is via measurement from the AFR gauge (which I acknowledge is grain of salt measurement) and examination of heads, spark plugs and header pipes. It's just that it gets way more obvious if I go up a hill (higher throttle) or start riding the bike the way it's meant to be used.

your calculation for amount of fuel required, is this for steady state? I ask this as I know someone who has a fuel rate meter on their dash, it’s acceleration which causes this to go min 3-5x more than highway (100kph) running fuel supply rate.

Well, I'd like a fuel rate meter. The calculation is for a theoretically perfect 900cc engine. 100% volumetric efficiency, perfect air-fuel ratio, etc. It's full of guesses. I took the 300 mL / minute figure from 100% throttle and thus 100% volumetric efficiency at 6000 RPM, the nominal peak output of the 900SS engine. It's a useful benchmark guesstimate number, that's all.

I am suspicious about the return line not being below the fuel level at all times. I wondered if the pump is unable to supply the instantaneous amount of fuel, fuel is then sucked down the line along with air. If this goes for too long air will enter the carb via the return line.

Yep, but the fuel pump is putting 5x the maximum expected demand along the feed / return line circuit. It'd have to be something spectacular happening for the carbs to suck the return line dry.

I would be keen to run a transparent hose from the Y to the tank to watch the fuel level.

Well, if it's working properly then that line will never show air. I'm confident that's the case btw, I'm just getting pressure variations due to velocity variations. What'd be more useful for direct experimental confirmation of what I'm guessing at would be some kind of ultra-sensitive fuel pressure meter, something with a decent scale from 0 to 2 psi or so. I'd connect that the carb supply line and see what I get. For the record, this is possible via a very tall length of clear piping and a T-joint, it's possible to work out the supply pressure via the density x height x gravity formula.

Everything system I have worked with, always uses the path of least resistance, air, oil, heat etc.

i would also apply soapy water in case of vacuum/airleaks etc.

like those off-road bikes with the fuel hose through the cap.

Vacuum: that thought had occurred to me - what if the tank breather valve has jammed? - but that's a brand new breather. The leaning out behaviour didn't change when I installed it. Tank fuel level or evaporation doesn't seem to affect it either.

As to vacuum leaks at the carb bodies, I'm confident that the seals are OK, I've had them apart enough times to be sure of the rubber gaskets top and bottom.

you have been very thorough and the explanations/photos are excellent so even a dummy like me can understand:Punk:

Thank you, I just hope that this is useful to someone else out there.

[pete376403]

Is the fuel entry to the carbs above the lowest point of the tank (or where the petcock is)? Why does it need a pump at all?

[OddDuck]

Is the fuel entry to the carbs above the lowest point of the tank (or where the petcock is)? Why does it need a pump at all?

Yes, but only just - the height difference between base of tank and carburettor fuel rail is tiny, only 100 mm or so. The carb fuel rail is also quite a bit forward of the petcock, which is at the base rear of the tank. It wouldn't take much of a hill climb for this to go negative. Gravity feed just won't work with this bike unless a pumped weir is used, as you propose.

I can see what Ducati were trying to do with this pumped, recirculating system. I just don't think they did their detail diligence on it properly. I think the basic concept is workable - it's just that a very low flow resistance Y joint is needed, and probably much larger tank piping and fuel hoses on the fast circuit. The 6mm from the Y to the carburettors is OK, as discussed previously.

I'll have a go at some numbers and see what turns up.

[OddDuck]

Right, some numbers.

I got curious and ran some more numbers for the OEM Ducati setup, this time including the Y joint. I had to take a guess at the K coefficient for a narrow angle sharp pipe mitre joint, so the following is very much pinch of salt stuff, but this time the pressure variation comes in at 21% between idle and full throttle. The Y joint makes things worse. Of more interest is the fact that having all this resistance on the return line serves to increase supply pressure to the carburettors - these pressures are 0.84 psi (idle) and 0.66 psi (full throttle).

I tried calculating losses through the petcock and found something surprising, fittings aren't really that important compared to long lengths of narrow diameter tubing or piping. There is a term but it's about a quarter of what the 5mm pipe and 6mm tube loss adds up to. If losses are to be minimised then as Ocean1 said, increase pipe diameter.

If I go to a gravity weir inside the fuel tank to regulate supply head and run a single 1/4" fuel hose down through the petcock to the carburettor fuel rail, variation in supply pressure between static to nominal full throttle supply falls to 7%.

If I manage to use both sets of internal tank pipes, with a second parallel supply through the pipe previously used as the return line, the variation falls to just 1.5%. If I go this way, I might have to find and install some kind of inline petcock though, otherwise I'll have to completely drain the tank every time I need to take the carburettors off.

In both cases the supply pressure is just 0.32 psi.

This low pressure might just be a problem, it's probably worth running some tests on carburettor float level variation with demand against fuel supply pressure.

[OddDuck]

I'm keen to take a measurement of what's happening inside the float chambers while the engine is drawing fuel. I'd like to confirm what's happening with the fuel supply lines and also have a play with the needle valve seats.

Unfortunately that's easier said than done. Riding and trying to take a look - forget it. Dyno - don't have one, therefore can't take the engine to full load while the bike is stationary. About the best idea I've had is to simulate the engine draw by draining fuel from the bowls at around the same rate as would be encountered if the engine was running.

Exactly matching fuel flowrates to throttle setting isn't important for this measurement. What I want to see is if the fuel level in the bowls changes with fuel demand, in short, how consistent the behavior of the floats and needle valve is under various different fuel flowrates. Ideally the fuel level in the bowl should be consistent.

I've chosen to use three small peristaltic pumps to provide the fuel draw. For those not familiar with this type of pump, it's a flexible tube run around the inside of a cylinder, in a U-shape. A rotor carrying several rollers pinches the tube shut at equal spacings around the enclosed perimeter. If the rotor is turned, the pinched zones move along the tube, giving a positive displacement pumping action.

A peristaltic pump can also function as a valve, if the pinch is good enough. If the rotor is stopped, there won't be any leakage flow through the pump.

I've set the three pumps up to run in parallel electrically. They'll have parallel fuel lines in and out, too, meaning that any one can function independently of the other two. I can draw fuel in steps of zero, one pump, two pumps, all three, even on a simple power supply like direct connection to the bike battery. The enclosure was used to shield the sparking of the open commutator on the pump motor; this work is going to end up with petrol fumes getting generated throughout the garage and I want to minimise the chances of ignition.

The drain fittings for the carburettors took some machining. It's not possible to just purchase these, as far as I found. There are certainly aftermarket drain plugs, but all of the ones I saw function the same way as the OEM Keihin ones - unscrew the entire thing and presto, the carb drains. There wasn't anything on offer which carried a tube fitting and a screw valve.

The drain fittings also aren't threaded. The OEM plugs are threaded with an M16 x 1 thread; this is a very unusual thread and would require purchasing tooling to duplicate. It's a bit pricey to buy an exotic die or carbide insert lathe tooling in order to cut two threads. In the end I realised that I could use the heater element support brackets from earlier to press the drain plugs into place and therefore didn't need a thread at all.

This has to hold for the duration of a set of measurements. I'm not going on the road with this, so that makes life a bit easier. There's no need for hose clips everywhere and I can use cheap transparent vinyl tube.

The plan at this stage is to set the carburettors up beside the bike on some kind of a stand, run the fuel lines from the tank to the carbs, set up the drain pump module somewhere above the floor (this'll keep it above the worst of the fumes), and drain the carb bowls back into the fuel tank via the peristaltics. Power supply for the pumps can come straight off the bike battery. The stand pipes that I've cable tied to the fronts of the carburettor bowls will let me see what's happening to the fuel level and I can mark off increments with a Sharpie as I go.

I haven't metered the flow out of the peristaltics yet, that'll have to wait until I have the rig as a whole in place. It'll be good to do that, I'd like to confirm that I'm getting a maximum of around 300 mL / minute, as calculated. The pumps are cheap aquarium dosing pumps off TradeMe and were quoted as having a flowrate between 19 to 100 mL / minute, presumably dependent on fluid handled and pressure gradients.

[pete376403]

Keep a fire extinguisher somewhere nearby. Move the other bike out of the garage. :-)

[AllanB]

So you now have two Ducatis in parts ?

[OddDuck]

No no, the ST2 is still intact and running. The whole point of all those measurements was to work out what was there without taking the clutch hydraulic system to bits.

Tempting though...

Thanks Pete - I've gotten away with petrol so far but yes there is always a first time!!

[OddDuck]

I took the first measurements today. Some interesting results...

First things first: I purchased and installed a fire extinguisher. Dry powder (messy but effective), bracketed for easy access just inside the garage door - it's where I can get at it if I've bailed out from a fire in a hurry. There's only about eight seconds of spray in the thing but it's way better than crossed fingers and hope. For the sum of $34 there's really no excuse for not having one of these.

The measurements themselves didn't exactly go to plan. I got the setup in place as envisaged: carburettors off the bike and on a stand, extraction pumps feeding back to the tank, stand pipes accessible and ready for marking. It all went fine until one of the cheapo peristaltic pumps started leaking petrol everywhere.

Stripping the pump down established that the silicone rubber tubing had cracked. Maybe the petrol had got to it, but I'm more inclined to think that the cheap pump had simply been sitting unused for too long and the rubber had finally let go. It's possible to spend hundreds on a single pump, I spent about $22. You do get what you pay for.

And then there were two... I kept going and found a few results.

1) Clutter on the fuel line really does affect float bowl fuel level. In-line fuel quick connect couplings, fuel filters etc will introduce supply pressure drops and therefore drops in fuel level with increasing fuel demand.

2) Needle jet seat size will also affect float bowl fuel level. This seat size is very important, if the seat is undersized then it'll be the dominant effect, stronger than having clutter installed.

3) Perfect float valve behaviour appears to be impossible. No matter how large a seat is installed, there will always be a drop in level with demand, it's just the way that the mechanism works. Ideally this valve would go from sealed to 100% flow instantly but it doesn't, there's always a proportional band between closed and full flow, and this affects changes in fuel level.

4) Float needle valves actually like vibration and intermittent flow, this helps them to operate closer to ideal.

5) As far as I could tell, float fall vs demand isn't linear: it rapidly falls to a given level and then holds there. There's a curve which levels off. The trick for tuning will be to get static level and full demand level as close as possible.

6) Misalignment of the needle valve seat broadens the proportional part of the response, the initial fall on the level curve.

The last one was a surprise. More about this later.

And numbers...

I didn't really take a proper measurement of what the pumps could do, but it looks like they can deliver 100 mL / minute, as advertised. That means that for full throttle, as calculated (not measured unfortunately), I need to simulate 300 mL / minute fuel demand. With one of the peristaltics down, the best I can do with this setup is 0, 100, 200 mL / minute.

Setup 1: 6mm hose directly connected to the tank and Y joint, an inline fuel filter and quick connect fitting between Y and carburettors, 2.0 mm needle valve seats. Fuel level fall between idle and 2 pumps was nearly 6 mm. I saw very clear progression in the stand pipes at each step.

Setup 2: 6mm hose to Y joint, 6mm hose to the carburettors, 2.0 mm needle valve seats. Improved behaviour compared to above but I still saw 5 mm fall.

Setup 3: 6mm hose to Y joint, 6 mm hose to the carburettors, 2.6 mm needle valve seats. Very interesting behaviour here: one carburettor saw nearly 6 mm fall, the other just 2 mm. The problematic carburettor had a 4mm fall between no demand and the first peristaltic, unlike the other, which moved by 1 mm or less.

At this point pump 1 managed to chew up its hose and fail. It was repairable but by this point I'd had enough of hanging around in the fumes and set about clearing stuff away for the day.

[OddDuck]

Something I noticed during the flow / level measurements: the needle valve seat is very slightly shorter than its housing. The retaining screw clamps down on the housing, not on the seat, as shown by the marks where the dished screw head has carved into the aluminium but not the brass. There's around 0.10 mm of float.

I've made up a pair of washers from brass shim stock and fitted these: 0.25 mm thick, 7.5 mm ID, 10.8 mm OD or thereabouts. The idea is both to allow the seats to be nipped up properly, but also to be held flat and square in their bores. The OD of the washer has to be smaller than the OD of the seat's locating face (in this case, on the other side of the seat). Pressing anywhere inside the circle will naturally press it flat.

IMG_2031 hopefully shows the two marks that the dished securing screw have left on the housing (6 and 9 o'clock), it wasn't easy to photograph this.

IMG_2035 shows the seats pressed fully home in their bores, no washer, and a visible gap between securing screw and the seat.

IMG_2044 shows the O-ring seal for the inlet snorkel. Apparently this is not necessary in non ram applications, my experience so far has been that without it, fine dirt slowly moves into the air jets and then goes through the carburettor. I've just fitted these seals tonight, haven't tried running with them yet.

IMG_2047 shows the seat reassembled with the washer fitted.

IMG_2051 shows the seat, washer, float and needle fully assembled - the seat should be square but due to the off-center screw, the washer has lifted a bit on the open side.

As to why I think this is important... three reasons, really.

1) consistency between carburettors when setting static float height.

2) seat height and thus float height remain fixed during carburettor operation.

3) the seat face is always presented square to the needle, this greatly helps the needle to seal properly and go from sealed to full flow in the shortest motion possible.

I'll have to make further measurements to be sure that this improves things. The last measurement of float height did seem to make a case for it - quite a large variation was seen between two carburettors running apparently identical settings.

The very fine washers were made by clamping shim stock between two plates, drilling the center hole, and then clamping again between two thicker washers on a mandrel to turn the outer diameter down. It was fussy but it was the only way I could think of to get these made without bending the edges of the metal.

[OddDuck]

I set the fuel measurement rig up again today to check the valve seat work.

A couple of changes:

1) the fuel drain pumps were now run off a regulated power supply

2) a stand tube was set up on the fuel line, at the carburettors inlet.

I'd rebuilt pump 1 and 3 earlier in the week with replacement silicone rubber tubing, slightly thicker walled than the original. This was better but still gave reliability problems: the rubber both swelled with fuel and also slipped under pumping action in the pump housing, ultimately bunching up on one side and jamming the flow. I had to keep pulling the tubes outward to get the pumps running again. The photo shows the pump assembly at the end of the day's testing, with the tubes just about pulled right through the pump housings.

Before starting work with the bike I checked output of the pumps, using a volumetric measuring cylinder:
Pump 1: 75 mL / minute
Pump 2: 92 mL / minute (still running the original tubing)
Pump 3: 75 mL / minute

I then checked flow with all three running simultaneously: 242 mL / minute, in short, they're adding up nicely and there aren't issues with non-linear behaviour on the drain side of things. All of this was done through the experimental setup so that pump behaviour wasn't altered.

The carburettor bowl stand tubes had a problem, last time around: the peristaltic pumps set up quite a bit of vibration in the fuel level and it became difficult to read them. Some damping of fuel motion was needed. I provided this by putting a double-ended cotton bud down the 6mm tubing. It let fuel through but stopped rapid motion very well.

Then to the bike... I started the fuel pump, watched the level in the inlet stand tube rise, tried running the pumps, and was very pleased with the result. Fuel level in the bowls dropped by 3 mm and was consistent over both bowls, with identical initial fuel heights. Later runs showed even tighter behaviour, approx 2.4mm between zero demand and full load. It looks like the 2.6 mm seats and the nip-up washers are working. I'd also guess that the needle valve's rubber tips bed in to the seats, if they're left standing for a while.

The inlet stand pipe showed me something interesting: I'd been correct about pressure variation on carburettor inlet with fuel demand. The pressure on the inlet really does drop with increasing fuel supply. I hadn't quite been right about how much it was, it was roughly 13% instead of 21%, but it was there.

The photo of the inlet stand pipe with four bits of masking tape on it shows this result. The two upper pieces of tape show fuel height (and therefore pressure via p = density x gravity x height) when the fuel pump is running. The highest piece of tape is for no fuel demand. The lower of the pair is for all three peristaltics running. This shows supply pressure variation of 13%, as measured by change of height above the carburettor inlet. This is for 242 mL / minute, of course. I couldn't measure for 300 mL / minute but if scaling is applied and the effect is linear, the variation will be around 16%.

The two lower pieces of tape show the same thing, with the fuel pump off and the carburettors now fed purely by gravity and siphon from the tank. In this case the supply pressure variation is much worse, roughly 45% or so. This is quite different to the 7% I'd calculated earlier, probably due to flow losses through the fuel filter. I'd calculated the 7% for the tank's internal piping and fuel lines only.

In both cases this didn't affect the zero to peak variation of the bowl fuel level much. It still stayed at a neat, tidy 3mm or so. What did change was base level. Between pump running or not running, the base height shifted by around 1 mm.

The same thing happened when I sealed the tank (so the tank breather valve came into play) and drained the peristaltics into a bowl: the inlet pressure to the carbs changed (it increased slightly), supply pressure varied by around 13%, carb bowl level varied by 3mm or less, but base height very slightly increased. It looks like fuel line supply pressure affects the point where the needle valve will seal off.

So as far as I can see, this does validate the Ducati design. It's not perfect, but it's as good as it needs to be. The Ducati fuel delivery system also gives supply pressure higher than gravity could manage, which probably helps, and it does it without using valves or diaphragms (as a pressure regulator would need) so long term reliability is good. Ultimately the only modifications needed to improve the system were a bigger needle valve seat and making sure that seat was properly mounted.

Modifications to actively avoid: doing anything to the fuel supply lines. The achille's heel of the system is that it seems to be horribly vulnerable to anything introducing a pressure gradient.

Anyway, it now looks like I have a stable foundation for proper carburettor tuning.

[OddDuck]

I made a modification to the way the carburettor breather line is arranged, after running a couple of fairly simple calculations. Previously I'd simply run a tube from the breather to a point where a fuel overflow wouldn't go all over the bike, as per every bike I've owned previously. That means a line run down the side of the engine, similar to the battery vent tube. This time around I've gone vertically upward and applied a crankcase breather filter to the end.

This is a violation of the normal experimental procedure, by the way. If you've got a multi-variable system and you want it to go better, change only one variable at a time. If you change two or more, and it goes better or worse, there's no clear explanation why.

If I get curious enough later, it won't be that big a deal to run a hose down as previous and see what, if any, change there is compared to the changes I've made in the float bowl already. For now, I think this is the most promising way to go.

The reason for this change is worth going through. It turns out that there's a bit more engineering in a carburettor vent tube than I'd thought.

Carburettors work, fundamentally, by a pressure differential pushing fuel into the intake airflow. There's got to be positive pressure (relative to the carburettor throat) in the float bowl chamber to do this. The usual story is that high air velocity through the carburettor's throat - the venturi - reduces the local air pressure, thus sucking the fuel in. The unspoken assumption is that the fuel bowl is (of course) at normal atmospheric pressure, easily arranged via a vent. There's a pressure push between the two, the fuel continually refills, no problem so no worries.

If there's a significant air leak between the float bowl and the throat, that's it, the carburettor won't draw fuel. If the carburettor vent is blocked, pressure in the carb bowl will drop to match the intake and again, the carburettor won't draw fuel. If there's a mispressure in the float bowl, it'll directly affect the air-fuel ratio, forcing it either rich or lean. If there's a variable mispressure in the float bowl, the carburettor will be impossible to tune.

None of this is from my own direct experience. These are all pretty common discussions on the adventure bike forums, since dirt getting into carburettor breathers is a fairly common problem.

I think it's possible that I've been seeing a speed-dependent mispressure of this type, as well as the fuel bowl draining to a low level. The old vent tube was arranged with a square-cut end, at roughly 90 degrees to slipstream airflow, at the front left corner of the engine. It's a very rough suction tube, in short, drawing air pressure out of the carburettor bowls and thus making the mixture leaner with speed. It shouldn't be a strong effect, but... how strong?

I don't have a wind tunnel. That'd be the way to really test this: set the bike into a wind tunnel, sitting on a dynamometer, and rig manometers at all areas of interest. Get local pressures at air intake, carburettor throat, carburettor bowl, vent tube, and anywhere else of interest with the motor running and under load. In the absence of this sort of facility, it's get the pen, paper and calculator out. The calculations below are riddled with assumptions and are best treated as a guide only, but still, after the experience with the fuel lines, I'm confident that they will show a trend.

First: Bernoulli's flow continuity equation. Along a flow streamline:

Pressure / (density x gravity) + velocity squared / (2 x gravity) + height = a constant

It's possible to relate flow in two different locations, different speeds, heights, pressures etc by this relation, as long as they're in the same streamline. In this case I looked at free flow in the slipstream, then a momentarily captured pocket just at or inside the hose opening.

It turned out that the pocket just inside the hose will see a pressure drop of roughly 0.46% of an atmosphere, at 100 kph. Absolute pressure in this situation is 100,862 Pa, compared to normal atmospheric pressure of 101,325 Pa.

That's not much of a difference, shouldn't be a problem... except that it's not relative to the atmosphere. It's relative to whatever pressure is there in the carburettor throat. So, using the same equation, assuming 100 % volumetric efficiency at 6000 RPM, full throttle, and flow through the carburettor only 1/4 of the time, I estimated carburettor throat pressure (absolute) to be around 98,535 Pa. That's against normal atmospheric pressure of 101,325 Pa.

I.e. 98% of the normal atmospheric pressure is still there, the carburettor operates to draw fuel into air on just a 2% pressure differential.

Right. Maybe this would explain why carburettors can be a bit fussy.

Looking at the 0.45% variation in light of this, between zero slipstream and 100 kph, there's suddenly a 17% variation in pressure between fuel bowl and carburettor throat, purely due to the fact that the drain tube ends out in the slipstream. If I placed it somewhere on the bike that was tucked out of the breeze, this effect goes away. Of course if the new location's ambient pressure doesn't match the intake ambient pressure, there's a whole new set of problems to sort out.

The next thing I twigged to was the reason that Ducati used a shrouded box to cover the vent tubes in the OEM Mikuni carburettors: it's not a cover at all. It's a resonator. The OEM Ducati design, shown in exploded view in the attachments (thanks Stein Dinse) clearly shows the use of Helmholtz resonation on the air pressure side of the carburettor. They've done the same thing they did with the airbox, though, and used a shared resonant space for two unevenly timed sets of pulses. The pulses will tend to mess each other up. The design shows two tubes going into one resonator, with the outer resonator apparently unused. It's been a while but from very vague memory I think the two resonators were connected via a hole, this might have been done to broaden the frequency response.

This would be done if there was a standing pressure wave set up in the float chamber by the action of the fuel being drawn, and if achieving resonance on the breather lines would help. This does, to my mind, make sense. Fuel isn't drawn continually. Instead there's a brief, fast draw during induction, then the bowl slowly refills during compression, expansion, and exhaust periods. It's cyclic and would look like a sawtooth wave pattern. Physical motion might be quite small but what's important here is the pressure front on the top of the fuel during the induction; if this pressure can't be maintained at some engine RPM band then there's going to be a lean spot in the carburetion. If this pressure is inconsistent due to RPM / throttle interactions then the bike's going to be very difficult to tune.

If there's a standing wave in the carburettor vent, installing things like in-line fuel filters would tend to dampen this out and thus wreck any resonance tuning that the manufacturer applied. The same would go for changing the length or diameter of the vent lines.

It's not really possible to set this resonator up on the Keihin FCR 41's. The two bowls share a vent line via a T-joint and so they talk to each other first and the air line second, plus the fact that there's a hard 90 degree angle between the single air line and either of the vent chambers means that waves won't travel through the system properly. Waves will travel back and forth between carburettors instead, assuming of course that they can channel out of the float bowls (there's another 90 degree angle here). It's entirely possible that this is deliberate design. The FCR's were always intended to go onto a huge range of bikes, fitted by owners as aftermarket upgrades, and so fussy things like resonators would probably be best avoided. For now, about the best I can do is to get the breather vent tube out of the slipstream, and into a zone of the same pressure as the intakes.

I've put the line up into the same under-tank area that the main pod filters are housed in. There's a crankcase vent filter pushed onto the end to keep the usual bugs / road grit out of the carburettor bowls but not affect the supply pressure too much (I chose the absolute lowest flow resistance I could find). Maybe it's too close to the inlets and will be affected by them, but there were limited options for placement. I might have better luck taking it forward and tucking it somewhere behind the front fairing. At this stage it's just try it and see. It isn't that big a deal to revert or change.

As a side note, the line's as close as possible to straight up. I'd read that any sort of loop in the line can trap fuel, and once that happens (under heavy braking or acceleration, say) it will eventually choke the carburettor bowl of atmospheric pressure and thus the engine will stop.

[OddDuck]

A very quick note - no photos sorry - filled tank with fresh petrol, made sure sump was full and tried the first start on the engine since rebuild.

No issues. Gave it a few squirts of the accelerator and then a few turns on the starting motor. It caught and ran. The engine made oil pressure after a few seconds (go moly-based assembly lube!) and after that it was good to give it some revs just to hear the sound again.

Very pleased. Miss my bike.

[BMWST?]

A very quick note - no photos sorry - filled tank with fresh petrol, made sure sump was full and tried the first start on the engine since rebuild.

No issues. Gave it a few squirts of the accelerator and then a few turns on the starting motor. It caught and ran. The engine made oil pressure after a few seconds (go moly-based assembly lube!) and after that it was good to give it some revs just to hear the sound again.

Very pleased. Miss my bike.

is there a more pleasing exhaust/inlet/engine sound than a ducati V twin?

[OddDuck]

I've been laying low on things bike and garage for the last few months while clearing debt. It's been frustrating but necessary. Having time but little of anything else, I'd spent a few hours contemplating a home dyno setup and going through the details.

Now, I want to be clear up front on this: I haven't built one, tested one, used one, hell I haven't even seen one properly. I saw a dyno setup being used once, on a car, from about twenty meters away. That's it, that's all the practical experience I've got here. Every word of what follows is old textbooks, pocket calculators, the internet, biros and refill, and more than a bit of OCD. I thought it was interesting and just possibly useful to someone, hence the post, but this really is just turning ideas over. The following is absolutely no substitute for practical experience.

I'll also skip ahead to the conclusion, so we get the disappointment over with: it turned out that it really doesn't make sense to home build one, at least not for me.

Estimated cost: $2000 and realistically my spare time for about half a year, that's if there aren't interruptions of course.

I have one bike to tune. One. Once. And summer's coming. I could really use that $2K to actually ride with. It really does not make sense to take half a year and take on another project, to end up with a one-use tool that's been used and now clutters the place up, if this was successful at all anyway. It might make sense if I had many bikes to tune, or on going tuning, etc etc, but at this time I don't. Maybe later.

So... the basics, apologies if I'm telling you stuff you already know:

A dynamometer ('dyno') will let you take your engine to full throttle, while measuring output in terms of HP and torque, but also monitoring engine behaviours like air-fuel ratio, ignition timing and whatnot. It's basically the Holy Grail of things garage and engine tuning. This is not easy to do. As such, they aren't cheap.

There are two basic types: Inertial and Brake.

Inertial is simply a massive rotating mass. The bike accelerates the mass and by dint of cleverness, data can be extracted.

Brake is the other type, capable of absorbing steady RPM and torque. It's way easier to read but much pricier.

Some types of brake dyno:

Friction - an axle with brake disc/s and brake caliper/s
Eddy Current - an axle with discs and electromagnets
Hydraulic Pump - a pump pushing oil through a needle valve
Fan - basically the bike drives a giant air fan
Water brake - a driven dished plate turns against a stationary dished plate, inside a flooded housing
Force lubricated, oil shear friction brake - basically a wet multiplate clutch

They've all got pros and cons but the most common is the Eddy Current.

I became curious about the last type, the oil shear, so spent a while playing with the idea. The basic concept is that it's similar to a multiplate clutch: driven discs alternate with stationary discs. There's shear in a fluid wetting the disc surfaces. The assembly center is pressurised by an external pump so there's always a positive pressure gradient in the fluid between the center of the discs and the outer diameters.

Basic formulae:

For two plates, one moving relative to the other, with a fluid between them:

shear stress = kinematic viscosity x plate velocity / plate separation

Force between plates = shear stress x plate surface area

Plates can be likened to discs, with an area and an average radius and velocity

Torque per disc pair = force x radius

Total torque = torque per surface pair x number of surface pairs

and torque required to be absorbed, RPM, power etc can be readily determined via the bike's specifications for engine and gearbox.

Of course it's basically just a clutch. I'd had the bright idea that I could make something that would replace the rear wheel. I'd counteract the torque via a handy through hole on the engine casings, with a spring balance measuring torque back to the body of the dyno. Presto, pop the bike up on a rear stand, remove rear wheel, fit dyno, take runs, success!

Yeah... cutting a very long story short, after many, many calculations, it turned out that doing things this way means that the dyno has to cope with massive torque at full throttle. 540 Nm @ 1500 RPM, with my bike in 6th gear and the engine held at 6000 RPM. That's the lowest torque situation I could set up at peak output for the 900SS. There are space constraints of course, limiting the diameter and number of discs.

The dyno's going to be absorbing between 60 to 80 kW of mechanical power. That's a lot of heating. I worked out that, to get around 10 C thermal regulation across the plate stack while under full load, I'd have to flow 2 litres of cooling water per second. That thermal control is needed because fluid viscosities tend to decrease significantly with temperature.

After some work with disc diameters and spacings, the reason for the pump pressurising the center became clear: the only way to get acceptable torques is to run the discs at tiny gaps. 50 to 25 microns, or similar. They're basically in contact. The pump is necessary to make sure that discs stay lubricated and won't bind together, despite the conditions.

Fluids: about the best I could find that was commonly available was 80-90W gear oil, with a viscosity of around 250 C.S. (centistokes), but it's rather temperature dependent. It gets slippy as things warm up. Golden syrup was contemplated (2000 C.S.) but again, same issue of temperature vs viscosity, and anyway I'd get a permanent ant infestation in the garage when the inevitable spills happened.

Finally I did something I really should have done first: I took a pair of steel clutch plates and had a play, first with golden syrup, then with gear oil. It was messy but demonstrative.

There is an effect. This idea does actually work. However it's a weak effect, even with something as heavy as room temperature golden syrup, the plates pretty much have to be ground into each other for there to be significant countertorque.

Further calculation showed that the bike-mounted dyno is possible. With 21 plates around 500mm diameter, 80-90W gear oil, and cooling, this could (in theory) just work. However it's pretty marginal, the space constraints of replacing the rear wheel really limit what can be done (about 80 to maybe 100 HP). In the real world I'd say a roller system built into some kind of structure is far more realistic.

Material: a full sheet each of steel and aluminium (as a bearing pair) would be needed for the plates, plus laser or water cutting, plus an axle, hub, housing, pressure plates at each end, seals, pressure pump, balance scale, RPM counter, etc etc... you'd be lucky to get away with $2K, or so I think.

Noise: this is full throttle sustained running in suburbia. It's not going to happen for very long before I'd have conversations with officials, unless I can build some way to effectively muffle the bike's exhaust note while not changing the engine performance.

Yep. Nice idea, good to play with, not going to happen. At least I didn't start spending money.

[AllanB]

Pretty sure you could find a company with a Dyno and talk a deal well under that value to tune your bike.

And the suburbia thing. Bugger em - run it during the week and make the bored housewives damp with the sound of a Ducati at revs :yes:

[OddDuck]

Very late reply... apologies! Yep a series of Dyno runs would be cheaper than what I worked out. It'd make sense to build / buy something if there were a series of bikes to be tuned, otherwise it's just smarter and easier to pay the pro's.

Just restarting work on the bike after taking a break. This time it's (finally) installing a brand new clutch basket.

I'm going to nerd out over this. For me this is a huge deal - both the 900SS and the ST2 came with 30K+ clutches and I've just never had the coin to sort the baskets. I've never had a clutch running with anything like a proper clearance between basket fingers and friction plate tangs. It's always been rattly.

The friction plates are getting replaced as well since there's not much point putting rattly old frictions into a nice new basket. It turns out that it's possible to buy friction-only plate sets - you keep the old steels and just sub in new frictions, which saves a bit of cash. Apparently this is possible on fibre / organic clutch plate sets. The friction material wears down but the steels don't. This particular plate set replacement wouldn't be possible if I was running sintered frictions, apparently these are a bit aggressive and take material off the steels over time.

A couple of notes:

The cheapo clutch locking tool works but could be dicey if dealing with a thoroughly dust-locked hub nut. Liam of Fastbikegear posted a while ago that these tools can damage the pump cover if too much torque goes through them... the pump cover is replaceable but not exactly cheap. The better versions of this tool use all four available screw holes. Neither is what a proper mechanic would use, since it takes a minute or two to fit the thing each time. I've got a proper clutch wrench on order from Oberon but it hasn't arrived yet.

The tap and button die are being used to clean old Loctite 510 off threads, nothing else - I like to reassemble with components as clean as reasonably possible. I'd read somewhere that torque settings are based on fasteners as delivered to the factory, which means clean, straight threads, lightly oiled (liquid Loctite is supposed to have the same lubricity as a general light oil, for this reason). It pays to be careful and steady when doing this sort of work of course, a snapped off tap or a crossed thread would be a nightmare.

The new basket is stock Ducati OEM. There's plenty of upgrade options around, in terms of performance, but stock is supposed to be the most durable. It's certainly the most affordable. Placing the two baskets side by side showed the difference between filed flat twice vs brand new.

[OddDuck]

... and the result. It looks like the Newfrens are alloy plates, which I hadn't expected. They should be quieter than steel, but I don't know if they'll last as long or if they'll be kinder to the basket. It'd be good if these things happened of course.

The gap's good though and that's the result I'd wanted. I imagine I'll have to ride the bike gently for a bit while the new plates bed in and settle down, Newfren left a note stating something along these lines.

[OddDuck]

First run of the bike showed clutch issues, yet again. The bike's got clutch drag at standstill, choppy gearchanges and it's pretty much impossible to get it into neutral with the engine running.

This was the reason for starting the thread about master cylinders going suddenly or degrading with time (general consensus was that they gradually lose performance due to corrosion and wear). Anyway, before going shopping, I tried a clutch system bleed to eliminate old clutch fluid as a variable. Earlier I'd purchased an ultracheap vacuum brake bleeder kit off TradeMe so took the opportunity to try this out.

Well, it draws a vacuum. Let's leave it at that... it doesn't work properly with the bleed nipple, but that isn't the bleeder's fault. The threads on the nipple have to be sealed against air getting in, and on this assembly they aren't, so most of the vacuum is lost to a constant stream of air bubbles. I went back to the pump lever-loosen nipple-bleed-tighten nipple-release lever procedure and did the bleed that way.

Fluid colour was good, didn't get any air bubbles out, slight improvement in clutch travel as measured via vernier caliper between spring cap and pressure plate. Travel went from 1.1 mm (!) to 1.3 mm.

It was while doing this that I noticed that the spring caps themselves - which are supposed to be fixed rigidly to the clutch hub - are moving inward and outward with the clutch action, following the pressure plate. This is soaking up some of the clutch travel. Not good... the clutch hub is the two-piece OEM Ducati item with cush rubbers and it looks like the pushrod is somehow interacting with these cushings. I had a go at photographing this but it turned out to be tricky. The motion is on the order of 0.5 mm and the camera wasn't rigidly fixed to the bike, so any lean on the bike would affect the photos.

[layton]

First run of the bike showed clutch issues, yet again. The bike's got clutch drag at standstill, choppy gearchanges and it's pretty much impossible to get it into neutral with the engine running.

This was the reason for starting the thread about master cylinders going suddenly or degrading with time (general consensus was that they gradually lose performance due to corrosion and wear). Anyway, before going shopping, I tried a clutch system bleed to eliminate old clutch fluid as a variable. Earlier I'd purchased an ultracheap vacuum brake bleeder kit off TradeMe so took the opportunity to try this out.

Well, it draws a vacuum. Let's leave it at that... it doesn't work properly with the bleed nipple, but that isn't the bleeder's fault. The threads on the nipple have to be sealed against air getting in, and on this assembly they aren't, so most of the vacuum is lost to a constant stream of air bubbles. I went back to the pump lever-loosen nipple-bleed-tighten nipple-release lever procedure and did the bleed that way.

Fluid colour was good, didn't get any air bubbles out, slight improvement in clutch travel as measured via vernier caliper between spring cap and pressure plate. Travel went from 1.1 mm (!) to 1.3 mm.

It was while doing this that I noticed that the spring caps themselves - which are supposed to be fixed rigidly to the clutch hub - are moving inward and outward with the clutch action, following the pressure plate. This is soaking up some of the clutch travel. Not good... the clutch hub is the two-piece OEM Ducati item with cush rubbers and it looks like the pushrod is somehow interacting with these cushings. I had a go at photographing this but it turned out to be tricky. The motion is on the order of 0.5 mm and the camera wasn't rigidly fixed to the bike, so any lean on the bike would affect the photos.


i had a smiliar issue with a 900 monster, i ended up cleaning the hell out of the slave cylinder bleeding it several times adding an extra steel disc to the clutch pack right at the back( stops the rattle at idle) and adding some washers to the pressure plate springs. seemed to work for me, also check ur clutch lever is totally disengaging, do you have after market leavers? they can cause issues like that, sometimes a few strikes with a file sorts them out. clutch drag issues that is

[OddDuck]

Thanks Layton - I do have aftermarket cheapo levers on the bike, these ones:

https://www.trademe.co.nz/motors/motorbikes/parts-for-sale/handlebars-handlebar-parts/listing-1778537543.htm?rsqid=fc9ecfde1e874bd3b9fa0515c416e e67

Yeah they're a bit cheesy but they've worked alright for the last couple of years. I took the lever off and stripped it to find (unsurprisingly) that it's got obvious wear at the main pivot point and also the position adjustment pivot - this wasn't arranged properly. The screw threads bear directly on a brass bushing and the screw has cut its way into the brass.

Both of these worn areas have affected the lever. Wear on the main pivot can be compensated by turning the spring loaded flat blade screw that drives the piston pushrod, but wear / cutting on the adjustor pivot directly reduces the lever-to-grip clearance and thus travel. It's possible to file the ball end of the lever flat and gain a couple of mm that way, this would mean roughly 0.07 mm more travel at the clutch slave but that's getting desperate.

Looks like it's time to replace or upgrade. I'm thinking at least Brembos - the main pivot is properly bushed instead of just anodised aluminium used as a bearing surface - or possibly Oberons if I can afford them.

No photos of this sorry - this was last thing last night and I was getting a bit tired - long day in the garage working out what was going on with the clutch hub and clutch pack.

[OddDuck]

Taking some proper measurements of what's going on with the clutch... I got the magnetic base and dial indicator out. One of the engine stand plates (from earlier) served to attach the base.

This worked a treat. Results, for six springs:

Pressure plate movement: 1.40 to 1.45 mm

Hub movement: 0.18 to 0.19 mm

I then took three springs off and remeasured. The point of this was to halve the clutch pressure force - if there's air etc in the hydraulic system, this test will show it up and it's possible to extrapolate back to zero clutch force, to what travel should ideally be.

Pressure plate movement: 1.47 mm

Hub movement: 0.17 mm

Then I took all the springs off and tried the clutch pressure pack take-up movement, by hand (not photographed but very similar). This was a surprise: 0.80 to 0.95 mm. That's a lot of spring motion in the plate stack.

Between the plate stack and the hub, almost all the slave cylinders travel is taken up. No wonder I'm getting clutch drag... 1.40 - 0.90 - 0.19 = just 0.31 mm nominal free play, and with plates rattling and bouncing there'd still be contact anyway... Hmm.

The last photo shows the OEM Ducati clutch hub on the bench, stripped down. The system uses a pair of cush rubbers, two between each fin on the inner and outer halves.

[OddDuck]

Something I wanted to check was how much free play was natively available in the clutch hub. As supplied, without cush rubbers, how much does it move? What's happened, given that this was a worn hub?

The hub was stripped and checked. Serious wear is visible on the inner flank, but curiously it's all on one side and only halfway down the diameter. A sideways look at a partial assembly shows that the cush rubbers don't set axial position - that would be set by the inner shoulder of the smaller locating diameter.

I reassembled the hub without the rubbers and then tried checking how much it can slide on axis.

2.75 mm

Oh Ducati. What have you been doing??

Yes, there's a bit of wear in the faces of the heavy cup washer, 6-point washer, all hub components etc... there isn't 2.75 mm worth of wear. Not a chance. Realistic figures for wear on the steel components are in the ballpark of 30 microns and the axial faces of the hub are similar. In short there's one hell of a lot of slack in the hub, I do not think that this is a good thing.

Thinking about it, this was probably a result of the vertically split engine cases. The gearbox input shaft already has shims everywhere - Ducati may simply have wanted to avoid yet another collection of shims and critical tolerances. All that this component really has to do is come up to an end stop and then stay there, it doesn't have to be shimmed against moving toward the clutch slave. Still, I don't like it.

The off-center wear on the outer hub's inner large diameter is also concerning. The hub's two main components, a cast steel inner and a soft cast aluminium outer, form a very basic dry bearing. They rotate a fraction of a turn against each other as the cushing does its work. If they're on center, the wear should be evenly distributed around the perimeter, not concentrated in a location. This indicates that it's been operating off center, skewed, and that would mean all sorts of clutch problems.

I think that would have happened if a few of the cush rubbers had bound up and twisted during assembly, forcing the hubs off-center. Some shreds of torn rubber came out with the cushes... a quick look at the hub showed some sharp edges.

[OddDuck]

I cleaned the assembly up a bit before reassembly, trying to ensure that the cush rubbers would slide in straight this time.

The inner hub is a cast steel component. The sand casting has left spikes, nodules etc over what should be smooth surfaces... cleaning this up took all of ten minutes, the steel isn't particularly hard and just getting the worst of the surface roughness off is enough. It's the same thing for the fin edges, just rounding these off a bit with a needle file will get the job done. Reassembly went fine.

Making a washer to take up the axial slack took much longer than I'd hoped, though. It turned out that the 6-point washer wasn't flat. It is very slightly dished - approx. 1 degree - and my nicely lathed up washer turned out to need tapering. I don't have a lathe at home and had to improvise, see photo. The method is to sand it down against a flat plate, but with the washer skewed off horizontal via a long spacer under one side of the washer. Push up and down, rotate, repeat.

Anyway, after much (way too much) sanding and trial-fitting of the hub, with cush rubbers removed, I had something I was OK with trying to fire up and ride on. The spacing is quite delicate: the hub shouldn't rattle, but shouldn't be nipped up either. To do its job, it still has to be able to turn. The 1 degree dishing would turn a perfectly flat washer into a bellville spring, which was exactly what I wanted to avoid, and a nightmare to size up accurately.

I don't expect the washer to last. The original Ducati components appear to be hardened steel, presumably the only way to make anything last under the constant grinding from friction dust, while the washer is soft aluminium. It's a first trial. It's never going to be 100% first time; there's always a bit of try and learn and try again going on, and in this case the 1 degree dishing screwed my sizing measurements. I measured free play again once everything was reassembled - plate stack, pressure plate, springs etc - and it was a disappointing 0.10 mm. Maybe that's a now undersized washer, maybe that's slack being taken up on the input shaft. Whatever, I'll run with it and see how it goes. If I'd been trying to resize hardened steel I'd have been there for a week.

The major benefit of this work may have been getting the cush rubbers to go into the assembly straight anyway. If memory serves, when I rotated the assembled clutch by hand, the friction tangs could be seen to wave in and out under rotation. They'd do that if the hub was skewed. Now they don't, they run steady. The clutch does appear to be releasing better when testing by hand with a shut down engine. This is good, but the acid test is to see how the bike goes while running.

I have another issue to address unfortunately so testing is still a way off.

[OddDuck]

A couple of quick notes before I forget, starting with a better photo of tapering the washer - I really should get a lathe but space at home is an issue. The stainless steel strip to the side got marked by loose grit, I wouldn't recommend using anything precious here.

It's a good idea to put something soft down on the floor while fiddling with clutch packs. I dropped one of the steels - from about 50 cm up onto concrete - and bowed the thing. It really didn't take much to knock it just enough that it shouldn't be reused.

[pete376403]

Can you imagine how empty your life would seem if you had a japanese bike? You'd have to waste your time riding:lol:

[OddDuck]

Can you imagine how empty your life would seem if you had a japanese bike? You'd have to waste your time riding:lol:

Bike Must Be Perfect

PERFECT


...why don't people understand??

[OddDuck]

And now for some Japanese carburettors.

I noticed while (briefly) riding the bike that the slides on the carburettors were rattling while the bike idled. They didn't do that before...

Bike's still (still!) running rough. If the slides are loose, ie not under positive control, it'd be very possible to get quite different idle / part throttle openings between the two of them, particularly with the engine shaking and throwing things around.

A quick look under the tank confirmed a loose slide - just testing it by hand showed free play of roughly half a millimeter, far more than was there with the carburettors new at roughly 25,000 miles ago.

Clearly something's got a problem. Opening the carburettors up on the bench confirmed the free play (on both slides) and some close examination showed the source of this problem: the rivets holding the red idler wheels on the yoke which controls the slide motion. The rivets have loosened.

There isn't much sign of wear through the carburettor bodies. The seals covering the vacuum plates are in good condition, so are the wheels carrying the slides themselves. The tracks those wheels run in are barely marked. Everything but these dinky little aluminium rivets looks fine.

Options:

1) get some sort of a clamp or vise onto the rivets and re-rivet them, all it'd take is nipping the thing up.
2) buy a new yoke
3) turn up some kind of threaded rivet replacement with a nut and loctite this into place.

Thoughts about the options:

1) piece of cake, get a suitable toolmaker's clamp and have at it. This time get a decent squish on the head, but try to avoid expanding the main diameter too much or bending / breaking the thing. The issue here is that the rivet came undone in the first place. There's a pretty good chance that it'll just do the same again.

2) wait for a new part (could be six weeks plus) and then wait again for the new part to fail the same way the old part did... but it will work for the next few seasons.

3) fiddly, time consuming, needs custom machining, but it's possible to match materials for things like thermal expansion. It's also possible to make it much stiffer than the original. Loctite obviously (might be hard to remove later if necessary), the big gotcha here is obtaining some sort of counter-torque feature on the inside side so that it can come apart again later. There just isn't much room.

[AllanB]

(2) be good for another 25,000. And you know something else will shit itself before that :shutup:

[pete376403]

The carbs were rattling before, you just couldn't hear them over the noise the clutch was making. fix the clutch, now its the carbs. Fix the carbs, it will be something else (loose rivets inside the exhaust cans, for example) Ducati Whack-a-Mole.

[OddDuck]

The carbs were rattling before, you just couldn't hear them over the noise the clutch was making. fix the clutch, now its the carbs. Fix the carbs, it will be something else (loose rivets inside the exhaust cans, for example) Ducati Whack-a-Mole.

Well... I was a good sport about this sort of thing before but maybe not this time.

If I post something, it's because I believe it's useful to someone else out there. That's it. Most of the work I'm covering these days is stuff that's completely off the manual and / or not covered elsewhere on the web, that's why I go into such detail about it.

The latest with the carburettors, for example... it's four cheapo aluminium rivets that somehow are affecting the entire bike. The job itself is almost trivial. It's just that as far as I've searched, nobody else seems to have posted about the rivets. The closest I got was a post on the ADV forums talking about the rollers having worn. There's quite a few of these FCRs out there. This problem will have happened on other bikes. Other riders could use this info.

Your latest replies are not helping with that.

I have little or no time for the game of Get One Up On The Other Guy, Pete, or the people who play it. Now you helped me out before and I appreciate that, but not the cheap shots. Try and be better than that, at least in this thread, alright?

[OddDuck]

Right, some work over the last week.

I've opted to re-clamp the FCR roller pin rivets. Relatively quick job, using a toolmaker's vise and winding it up via an Allen key - seems to have worked so far. The rivets aren't loose any more. The slides still have free play though... this will reset a rivet, it won't compensate for wear on the roller wheel.

While I was in I also rebalanced the carbs, using a drill bit shank as a feeler gauge instead of comparing vacuums. The balance adjustment is via a very cute push screw and pull nut, which raise and lower the yoke arm on the throttle shaft. They lock against each other but otherwise don't restrict each other, however it's generally best to loosen the nut first. It is possible to balance the carbs via vacuum, it's just that it's much faster and easier to do it this way.

The brake and clutch levers were improved. This turned out to be as simple as changing the bolt on the position selector pivot... the original uses a threaded portion of the fastener as a bearing. The marks can be seen inside the brass bushing. It's also carved its way into the aluminium of the lever itself. The shouldered bolt that I wanted (shoulder anywhere it functioned as a bushing, thread after that) turned out to have to be cut down from an M5 x 50 cap screw... I had to use a die and die stock on the original fastener to get a thread of the right length, then shorten the screw to suit. Such a small thing - roughly 10% of clutch travel was restored by doing this, the lever has gradually been getting closer to the handlebar due to the screw thread cutting into the bushing.

The surprise from the week was found while working on the ST2's clutch. I finally compared a near new clutch basket with a very well worn unit. Guess what... Ducati actually did get the axial clearance right, a brand new unit has very little free play on the gearbox input shaft. The 2.75mm clearance seen earlier was due to wear. Whoops. My mistake.

The broad, flat, 6-point washer cuts its way into the aluminium clutch hub over time. This is shown clearly in the last photo, the two hubs side by side are from the same manufacturer, it's just that one has a lot of k's on it compared to the other. The washer has sunk its way down into the hub. I've never seen anything like this before.

I don't know what the wear mechanism is. The washer is a near perfect fit to the worn hub, there's no looseness or free play. It sockets into place perfectly. A mystery, but for now I'll simply take it as proof that I should replace the hub currently in service.

I did manage to get the bike out for a brief ride which was pretty good.

[OddDuck]

The ongoing mission to sort out why the hell the bike is running badly continues... I've been at it again off and on for the last few months.

The first suspect was failed crimp connectors in the wiring loom to the coils. This came about after noticing heat damage to one of the connector boots.

The connector is carrying 12 to 14 V to a load resistance of 5-ish ohms - that's around 2.25 Amps current. It doesn't take much of a resistance on the crimp itself to turn a previously healthy connector into a minature heater element.

After replacement (some wiring included) and refitting - nope, it wasn't that.

The next suspect was the fuel pump and the wiring to it, the stuff that goes through epoxy in the connector under the tank. A pretty quick voltage over the pump test showed it was fine - and getting a mechanic's mirror and a penlight into the tank showed that the pump was putting enough fuel through the line that the return was basically a fountain. The pump terminals are accessible without disassembly, if you have long enough test leads or can improvise them.

[OddDuck]

I got stuck into thinking about the ignition setup last night, after noticing minor damage to the coil HT leads insulation from contacting the battery box. Why were the coils and modules so close together, was this a problem and why? I did a lot of reading and realised something - I haven't paid any attention whatever to the ignition coil's magnetic circuit.

The bike uses an inductive discharge ignition - transistorised is the term frequently used - which depends on energy stored in the inductance of the coils.

I found a very good document online from McLaren Electrical Systems which discussed CDI vs Transistorised Ignition Coils. Key points of Transistorised Coil Systems were:

- the coil stores energy as well as acting as a voltage transformer

- coil inductance must be relatively high

- switching rate is limited by time to charge the inductance

- primary voltage is low and current is high so connecting cables must be thick and short

- magnetic circuit design is critical and can be affected by location in the engine

- burn time is long

- EMI (electromagnetic interference) is severe in high performance systems

Food for thought. Is it possible that the coils are interfering with one another, not electrically, but magnetically? Is it also possible that the HT leads (which are rubbing on the steel, non-grounded, battery box) are coupling to input wiring via stray capacitance?

Further checking showed me something else. The coils are mounted in what originally looked like a strange arrangement: there's a threaded spacer which is bolted to the coil bracket. The coil is then screwed to the spacer. There's a fastener at each end of the spacer. Odd. Why not just use a through bolt and a nut?

It turns out that this aluminium spacer functions as a magnetic insulator post. There's something called permeability, the ability of a substance to carry a magnetic field.

Air, most plastics, aluminium, water, bone, wood... these all have the same permeability as free space, i.e., not much.

Magnetic steels, ordinary steels, iron etc has much higher permeability - around 4000 times as much. It's very non linear.

I've cut the aluminium spacers right down in order to get the coils and HT leads to fit (just) into the home made steel battery box. The spacers originally had 5mm space internally between fasteners. They now have around 0.25 mm (I spent a while being picky and making things only just fit). If there was magnetic impedance there, I've greatly reduced it.

The other thing is that the steel Ducati OEM coil mounting bracket, which originally fit onto an ABS airbox, is now mounted directly on a thick walled mild steel battery box. The steel is thick and wide enough to be comparable in cross section to the coil inner laminated core.

I have no idea how to measure or prove this, but it looks like I've mistakenly installed a magnetic short circuit network.

The coils on the ST2 are set forward, on outside and opposite sides of the frame. They're barely tucked away inside the side fairing panels. It isn't possible to get them further away from the rest of the bike, the control wiring, ignition pickups, ignition control module or each other. They're also mounted on aluminium brackets via rubber grommets and feature what look like completely closed iron cores. It couldn't be more different to the basic design on the 900SS.

The ST2 has run like a charm in the entire time I've had it, the ignition and fuelling have always been super smooth. Maybe this is the next thing to try - separate the coils and get these mounted in similar physical placements.

[SaferRides]

Yes, the coil mounting can be important. Also whether or not the secondary is grounded, although get that wrong and they tend not to work at all.

I certainly wouldn't put coils inside a steel box.

Can you easily go back to the factory mounts?

[OddDuck]

The yellowish bracket is the original factory mount and the alloy spacers mounting the coils can be replaced, so, yes, not really an issue. Refit the original ABS airbox and I'm back to the stock system. There were issues with that setup which was the reason to go to pods, which were the reason to replace the battery box (which was part of the airbox), etc etc.

The main issue to my mind with a return to stock is that it was compromised design in the first place. It works - but not well...

- coils right next to each other and 270 degree timing
- coils mounted on a common bracket made of a high permeability material
- coils under fuel tank, effectively a three-sided metal box, well it's good for keeping the rain off
- ignitor units and pickup leads right next to coils and HT leads

Anyway I'm keen to try a rough copy of the ST2 arrangement. Shouldn't be too hard to trial a setup.

[OddDuck]

Right, have put the coils onto the flanks of the bike - see photos. The coils are mounted on non-magnetic plates which have basic vibration isolation. I haven't weather sealed the LT connectors yet, wanting to keep this easy to work with for now.

Testing showed that this is working, there's clean idling and then advance to the maximum position on both cylinders.

While doing this I finally noticed something about my cheapo fabulous Supercheap Auto timing strobe gun: the inductive pickup has a direction. The arrow on the top points to the spark plug, as properly clipped onto the relevant HT lead. I've carefully coloured it in via Sharpie so that the thing stands out for the picture. Normally it's just moulded plastic which is all the same colour, hence my total failure to notice it. Clip the pickup on backwards and the gun simply doesn't work.

I've spent years thinking that there's something untraceably weird going on with the ignition for the horizontal cylinder. Gun just won't fire. The ignition has been fine all along, the issue is (and always has been) that the HT lead for the vertical cylinder goes to the right, the HT lead for the horizontal cylinder goes to the left. That's all it took. Whoops.

Right... putting that aside, I might have something useful for anyone running FCRs on a twin: it's possible to vacuum-synchronise them. All you need is reasonably quick access to the top cover plate of one carburettor. In this setup I have the throttle cables disconnected. Pop them out of their mounting rubbers, take the top plate off, and move the slide position by a marked increment via tweaking the pin screw and nut on the slide yoke. Reassemble, re-test, move again as needed.

Anyway, the bike's running, still running rough though. Attention to the carburettors looks like the next step.

[OddDuck]

I've attached a chart of Keihin's FCR needle sizing and their geometry. I'd had EMT's supplied with the carburettors and for a long time I've been thinking that they weren't right for the pod filters. The carbs would run OK at about 1/8th throttle to maybe 1/4 and then get progressively more and more lean. After another effort tuning recently, attempting to sort the super rich behaviour at and just off idle, the bike's lean as soon as it's on 1/8th throttle. According to the tuning chart, that's when the needle root diameter becomes the dominant variable.

I'd taken a punt earlier on a pair of needles with the next steeper taper angle, FMU's by code. I hadn't properly appreciated the importance of the root diameter: they're the next step bigger than the EMTs, and the bike simply wouldn't run past 4000 RPM or over 1/8th throttle. It just bogged out.

So... a pair of useless carb needles, which happen to have the taper I want. I've got another order in, with a series of F taper needles in various root diameters, but from experience it could be six weeks before delivery. So: the current FMU needles are expendable, it's not the end of the world if I stuff them. Is it possible to reduce the root diameter to a controllable number while keeping this d1 straight?

Some careful work with a micrometer, 800 grit paper, a drill press on roughly 750 RPM, and a rough tool to try to keep sanding pressure even along the length of interest, and the answer is a very conditional yes.

It can be done (sort of), it's painstakingly slow and fiddly, and there's a very high chance of bending the needle along the way. Rotating speeds have to be kept low. Initially I tried in a Dremel and it doesn't take much in the way of RPM before the needle starts to bow, if I hadn't been ramping speed up gradually it would have been very easy to bend the needle purely by spinning it.

Cutting speed (ie diameter reduction) depends greatly on pressure, if the paper is squeezed directly between two fingers then the cut takes off and also tends to dish. This can be useful if sorting specific marked areas along the d1 length though.

I managed to reduce both needles from 2.785 mm to between 2.755 to 2.760. There's no way they're as straight or precise as stock needles. However I now have a pair of FMR-ish needles and these should give a slightly richer mixture at 1/8th throttle. I haven't had the chance to try them properly yet.

[OddDuck]

While playing with the latest round of tuning (sorting the mixture at idle, slow jets etc) I noticed inconsistency in the idle mixture, as shown by the AFR sensor. It'd indicate variation from 12 to nearly 17.

Rattly slides. OK... maybe they're rattling far enough that the vacuum breaker plate is opening up, letting more air in than is supposed to be there. The rattle back and forth wouldn't be in sync with the engine vibration, hence the variation. I tried revving the engine a bit and listened closely: the rattling doesn't appear to go away with revs. It gets quieter, and certainly gets covered with other noise, but it's still there.

The way that Keihin designed the FCRs is based around a solution to a problem: simple slide carbs tend to stick at partial or closed throttle, due to high manifold vacuum. Keihin's solution was to use a vacuum breaker plate, which reduces the pressure differential to the point where there's minimal clamping force, while still controlling airflow.

The vacuum breaker plate is carried in a slide, equipped with rollers. This slide also carries the needle. The rollers are some kind of high-grade engineering plastic, made to survive heat and petrol. Three of the wheels are mounted on roller bearings, the fourth (right upper I think) is pure plastic and very slightly smaller than the other three. The whole thing rolls up or down in a rectangular chute in the carburettor body.

Basically, the vacuum plate controls airflow. The slide governs position and copes with force from pulsating airflow, keeping the vacuum plate in place as lightly as possible.

This very light placement is necessary for two reasons:

1) the lighter the contact force, the longer the vacuum plate / carburettor body interface surfaces will last against wear.
2) light placement force (and immunity to vacuum force) means a light throttle action. The throttle will close properly when released and won't require a strong twist to open again.

The photos show the seal between the vacuum plate and the slide - from the edge, it's a tapered, face contact seal. There's a small amount of squish range available which it'll seal over, ie there's a tolerance for the slide moving inward or outwards inside the carburettor body. It's not a broad tolerance and the way this seal works, it'd be best if there was no movement at all.

The issue with the FCR (these ones at least) is the free play in the slide assembly. I managed to get a 0.203mm feeler gauge to fit between roller wheels and their tracks in the carb body.

[OddDuck]

Limited to 6 photos for previous post.

The first shot is a tighter pic of the slide and sealing face of the breaker plate.

The second shot is a look down the slideway of the carburettor: I've found a couple of dips in the rail surfaces, apparently due to wear. They look like they match the wheels and there seem to be two sets, one at idle and another at my most frequently used open road throttle setting. One of these dips is center in the photo. It seems very small and was difficult to get a picture of unfortunately. This is on the vacuum plate side, so would actually increase clamping pressure on the plate. The inlet side's slide surfaces still looked OK.

The last image is the shot of the test for whether the slide clearance lets the vacuum breaker plate open up: lay a ruler or straight edge between the two lower slide wheels, with the feeler gauge in place to simulate the slide having been thrown forward and away from the breaker plate, then see if there's a visible clearance. A torch behind the ruler helps.

Yep. There is a clearance on this unit, albeit very small. It's opening up due to vibration.

Maybe the wheels have worn a bit and lost diameter, maybe I've lost material from the rail surfaces. Maybe both. Anyway, if this has been happening, what this means is random, cycle by cycle variations in air fuel mixture, which might explain persistent rough running.

There's a second, very good reason, to sort the rattle out. It hasn't happened to me (thankfully) but I've read reports of the vacuum plates breaking up and then being sucked into the engine. Being hammered back and forth isn't good for anything and these are simply cast aluminium.

[OddDuck]

After measuring slack clearance at 0.203mm, I had a try at shimming and found that a clearance is needed for smooth operation. My shims ended up at 0.127mm, which seems to work OK.

The shim material is brass, not stainless. Brass obviously works, that's what jets etc are all machined from, and I was concerned about the galvanic reaction between stainless steel and aluminium. Fabrication didn't require much gear: drilling between washers, tinsnips, 800-grit paper (for the edges), folding in a bench vise, etc. I used a Dremel to carve the oval slots and should have done the round edges for the throttle throat in this way instead of tinsnipping them. There was a lot of back and forth fine-tuning to make sure that the shims didn't bind up the slides.

I also wanted the shims positively retained, hence the fold and attachment through the carburettor top cover. If these move, bend, bind or jam, they'll jam the throttles. The far end of the shim plate locates into a narrow gap between two bits of the throttle body so that's supported. The brass is very soft and appears to have picked up wheel marks already, so I'm not sure how long (reasonably) I can expect in terms of service life. They're easy enough to pull and inspect.

Anyway, results: highly effective at stopping slide clatter and rattle, also effective at restoring consistency to idling mixture. This shimming has affected tuning. The vacuum plate leakage effectively leaned out the mixture. With the rattle reduced, the idle and just off idle tuning has become richer.

While doing this work I noticed a few fine shreds of rubber caught in the retaining spring of one of the slow air screws. It looks like the ribs on the pod filter necks were being cut by the carburettor trumpets on refitting. I've taken some paper to the trumpet edges and smoothed off the radius.

The photo of the red coiled air line hose might be useful for someone on a budget, or with limited room: it's a one-shot air duster. Very useful for cleaning out carburettor jets. The bicycle pump (which I owned already) will go up to 120 psi. The hose, gun, nozzle etc was purchased from Repco on special for $20 and all it took to connect to the bike pump was an old inner tube valve and a hose clip.

[OddDuck]

Some further work - I'm still trying to smooth the bike engine out a bit.

I've put a baffle between the pod filters. The reasoning for this is that, given the bike's asymmetrical induction timing, one intake will steal from the other if given half a chance. I'm sure that this is the reason that the ST2 features an airbox with a center divider.

The baffle was worked up via cardboard and a bit of fitting and filing. The black patch stuck to it is a bit of stick-on Velcro, used as an anti-rattle measure. Clearance to the internal roof of the tank cavity is around 4mm, give or take. Working this up took most of a day.

The second thing was the installation of an O-ring seal on the emulsion tubes. This followed detail measurements taken on the premise that it just might be possible for me to turn up my own emulsion tubes. I decided against, in the end. Too much work. However it did highlight something: the tubes carry petrol on the inside, with flow governed by the needle. On the outside, where they're not supposed to flow, they're sealed only by a close fit between a 5.5mm shoulder and a reamed hole in the carburettor body. It's a clearance fit, metal to metal. There isn't a compressible sealing element. It's totally dependent on tight manufacturing tolerances and the clearance not having opened up via mileage, thermal expansion and contraction and subsequent wear, or the engine shaking like hell and thus rattling the tubes (as might happen during a main bearing failure, for example).

Philisophically speaking, that means it leaks. No question about it, the metal isn't tight. The question is then, how much?

The detail measurements, and running some numbers, told me that it's significant in terms of carburettor tuning. Without actually taking measurements or documenting flow around the outside, on the horizontal cylinder, the clearance amounts to roughly 9% of the flow area inside the tube, with a perfect bore and a perfect needle. On the vertical cylinder, it was 20%. That's enough of a mismatch to cause issues.

The small bore transfer gauges pictured were used to help with making sure that the O-rings would make it into place without getting carved up by either the emulsion tube thread or an internal shoulder. The gauges aren't all that precise, unfortunately. I had to make sizing calls via guesswork: if the 5.5mm hole has been reamed, what are the standard tolerance classes of reamers used, etc. The hand drill and Dremel burr shown were used to open out the thread, clear the sharp-edged feed passage, and put a taper shoulder into the carburettor body bore, with final finishing of the taper surface done by very lightly twirling the burr by hand. It was pure chance that the OD of the burr was 6.35mm and that the taper was about right; the O-ring in its groove was between 6.30 and 6.35 mm OD. And so on. Tight clearances, fiddly and careful work. I can see why Keihin didn't do this.

While I had the carburettors apart, I took a close look at the emulsion tubes. These are a wear item, since the needle runs in them. They're scored. There are vertical lines of wear running in them. That isn't really surprising, with over 20K miles on them, and I've ordered replacements. Cutting O-ring grooves into worn-out emulsion tubes therefore sounds like a waste of time, but I wanted to test my theory: that leakage around the outside of the tubes was causing some of the engine vibration. The only variable changed was that O-rings were installed.

End result: both the baffles and the seals helped. I tested these one after the other so can be sure of that statement. They have helped, they're worthwhile. They haven't brought the bike back to 100% the way it should be.

The annoying bit is that I'd gone for a ride, pre O-rings and baffle, and the bike had been rough as guts until I'd parked for lunch. After lunch, for ten minutes or so, it had been as smooth as it had been earlier. I don't know for sure why. My best guess so far is that enough petrol had turned to varnish on the emulsion tubes that it had covered the scoring and the leakage up.

[OddDuck]

I've put some aftermarket LEDs onto the bike - both a pair of positioning lights and a pair of auxiliary headlights. The positioning lights have tucked onto a bracket underneath the front fairing. The auxiliaries are mounted on outrigger posts attached to the bike via frame clamps.

The reason for doing this is pretty simple: be seen, avoid SMIDSY. As a bonus the auxiliary headlights complement the low beam headlight very nicely despite the difference in colour.

The mounting pattern was chosen for a couple of reasons - I wanted to make the bike as visually wide as possible, also with a broad frontal area vertically. The reason for this is both to get seen and also to give drivers a wide target to estimate oncoming speed and distance properly with. It's difficult to do this with a single point source such as a single motorcycle headlight.

Kevin Williams - of Science of Being Seen fame - covered this point in his talk at Shiny Side Up. The research clearly indicated that cage drivers had a tendency to see bikes as further away than they were, and also as moving more slowly than they were, simply due to how small and narrow the bike is compared to a car.

The trick is to make sure that it's still recognisable as a motorcycle. Hopefully the yellow headlight will help with that.

Part of my installation has the auxiliaries back a bit on the frame so that they're side-lighting the fairing flank, front guard and front wheel. That's so that the bike's obviously a bike, when seen at a side angle at intersections, rather than some random pattern of lights floating around in the dark.

[OddDuck]

Well, I've been annoying the neighbors all weekend. Still trying to get the bike running acceptably, am finally feeling like I'm getting somewhere... I'm writing this up now while I remember what I've been doing.

I noticed a while ago that the bike has different length headers prior to the cross. The exhaust system is fairly simple: a curved header runs from each cylinder head into a four-way cross, which then feeds twin silencers. The headers enter the cross facing each other, but there are curved guides halving and feeding each header ninety degrees each way into the twin exhaust outlets. The header pulses end up running side by side in the same directions, not into each other. There is no provision for expansion, as more modern systems tend to do where two pipes join. Effectively it looks like the outgoing blast from each exhaust pulse is intended to venturi / siphon the other header pipe whilst keeping header diameter constant all the way to the muffler, also halving the resistance to flow by using both mufflers simultaneously. This may not be what's actually happening though. I've dredged up a few old photos, hopefully these show what the cross looks like.

It's quite different to modern exhausts. Most current performance V-twins use a two-into-one-into-two configuration, with Y joints and pipe expansion. Headers appear to be equal length - curled if necessary - and the Y joint angle is fairly shallow, not 90 degrees. Ducati themselves have moved away from the cross, finally.

I've spent a few days reading The Scientific Design of Exhaust and Intake Systems, Philip H. Smith. The book's rather dated but good. There were some key points I took from it concerning this particular exhaust system:

1) The whole system will pressurise every time there's an exhaust pulse, from header right through to tailpipe. The piping gives a flow resistance, the silencers as well, plus there's pressure wave behaviour to consider.

2) The waves can be around a third of an atmosphere in pressure, both positive and negative magnitudes. Negative pulses in the exhaust help to start to fill cylinders when there's valve overlap, positive pulses on both induction and exhaust sides help to tamp cylinders extra-full just before inlet valves close. The effect on tuning can be pronounced and timing is critical.

3) Getting accurate charts of these waves (pressure vs crank angle) could be done in 1967 or earlier, via a very clever arrangement of crank-driven disc valve, single pressure tap on exhaust piping, and around 32 mercury manometers being fed one by one off the disc valve.

4) The cross may not be functioning as a one-pipe-helps-the-other venturi properly. Smith was very clear that pressure pulses can go around corners, and certainly any pressure pulse coming back from the silencers and tailpipes would go to both cylinders.

5) The different header lengths may have been an attempt to compensate for the different dwell intervals inherent to V-twins in the exhaust timings. This would work perfectly at one engine speed, although it might be possible to broaden the response over a fairly wide range of RPM via tricks with conical megaphones (visible on the front of the silencers, with parallel perforated pipe inside) and tuned interference or resonance with the non-flowing exhaust header.

6) If there are differences in exhaust vacuum at the start of the induction cycle, when the valves overlap, this would directly affect fuel/air intake and thus carburettor tuning. The two carburettors won't be tuned the same.

With this last in mind, I connected the vacuum gauges to the inlet manifolds and tried winding the damping valves all the way out so that the needles tracked variations in vacuum, not the average. This very clearly showed that the vertical cylinder has a wider variation in vacuum than the horizontal, at least at idle. The gauges couldn't respond quickly enough to keep up with variation at higher RPM. I swapped gauges between cylinders to confirm. I tried photographing this: the vertical cylinder's gauge is the lower one in the photo. The needle motions are blurred but there's an impression of the angles they have both swung over.

I've been wondering why the vertical cylinder keeps on fouling spark plugs, while the horizontal comes through just fine. It's been doing this the whole time I've had the bike. I've checked or changed pretty well everything except the exhaust system. High vacuum spikes coupling through to the induction would tend to pull fuel, maybe quite sharply. No wonder it's had problems with running rich on the vertical for apparently identical settings and timings.

While running more tuning attempts, I swapped the wide-band O2 sensor over and confirmed the effect. It's a difference of at least 1 full AFR point. This will only show up if the sensor is connected directly into a header, it wouldn't show on tailpipe sensors since the mufflers are shared and thus carburettor tuning becomes averaged out.

It now looks like I have to road-tune one cylinder, swap the sensor, tune the other, then confirm that tuning on the first is still OK.

[OddDuck]

Further progress (of sorts)...

The throttle gauge has turned out to be very worthwhile. The cardboard gauge pictured previously has been replaced with a one-part disc cut from some coreboard (old real estate sale sign), cable tied to the Oxford hot grip and marked out to line up with the split in the throttle twistgrip mount. This is very readable while riding, and is also possible to lock exactly in one place due to friction between the cable ties and the twistgrip clamp.

This precise readability of the throttle gave an unexpected result: the tuning is changing while at constant throttle and constant engine load.

Initially I thought it was a headwind affecting pressure of the breather line, since this is now tucked inside the front of the fairing. I'd gone out to Wainui Beach with a tailwind and the bike running on the lean side. Coming back into the wind, the bike riched up by at least a couple of AFR points, then suddenly leaned out and stopped. Engine stoppages happened a couple more times on the way home. I'd pull over, wait about ten seconds, and then it'd restart just fine. This had happened earlier after Shiny Side Up (just once) and I'd been blaming it on the ignition, but this time a look at the transparent Y joint in the fuel lines showed the fuel bubbling merrily backwards out of the carburettors.

Ah ha. Vapor lock. Maybe the fuel was being overheated due to slipstream off the oil cooler. I moved the fuel line upwards so that it is in ambient slipstream and went out for another evening ride, this time over the 'takas.

Same thing. Just fine going over, then multiple stoppages on the way home. Whatever was doing it, it was getting worse. At the same time the AFR gauge was clearly showing the fuelling moving all over the place - sometimes rich, sometimes lean, and every time the bike stopped it was showing a super lean condition leading up to the stoppage. I finally twigged that there was a pattern: the bike would run consistently rich at low fuel demand, but start running lean and then have intermittent lean outs at higher fuel demands. It was about fuel consumption.

I'm not quite sure now how I noticed this, but the roadside test was simple: open the fill cap. If there's a pop on opening and the cap jumps upward, the tank's been at positive pressure. If there's a rush of air inward and the cap doesn't jump, it's been at negative pressure. These were linked with what had been going on. Rich: positive tank pressure. Lean: slight negative tank pressure. Stopped: definite negative tank pressure.

So, the breather valve clearly wasn't working properly. I took it apart and found a design mistake: it's possible for the thing to latch down and close up completely under sustained high fuel demand. This is where the engine stoppages and apparent vapor lock issues come from. I've tried to show how it is assembled in the attached photos. Something the photos don't show well is the slightly raised thin wall spigot on the tankward side of the assembly, the one with locates and centers the thinner, softer spring. Once the flat disc is sucked into this spigot, and then stuck on there by sticky old fuel, it isn't really coming off again. The spring isn't powerful enough to lift it off. Positive pressure in the tank will open a small gap but not blow it off completely, so it'll sit there until the next time. Problem. I found a fix: take a Dremel to the spigot and castellate the thing, get the finest burr possible and cut in-line slots into it so that even with the disc in contact, it'll still breathe.

This appears to have sorted the stoppages. It hasn't sorted the variable tuning though.

It's simple enough: if there's an increase in the tank's ambient pressure, there's an increase in the supply line pressure. That means that the needle valves in the carburettors have to seal harder. They'll only do that if there's a higher fuel level to force them closed. So changes in the tank's above fuel surface pressure will couple through directly to carbie tuning, by altering the float height.

The breather valve, as designed, basically causes this. It features spring loaded rubber seals in direct contact with metal. It requires a slight vacuum to open, and a positive pressure to open again the other way. The tank vacuum comes from fuel being drawn to feed the engine. The positive pressure comes from fuel evaporating and increasing gas pressure inside the tank. The two effects appear to have a cross over point where evaporation will match fuel draw; I think it's strongly ambient temperature dependent and in real world riding this seems to happen at around 80 km/h.

I can't be totally sure what these positive and negative pressures are, or what difference they're making in float height. I am sure that the pressure changes are quite significant compared to the very low supply pressure to the carbs. In a sense they don't matter anyway; the important bit is the difference in tuning, which I can see. I think it's around 2.5 to 3 full AFR points, with a time lag, which effectively means that fine tuning the carbs is impossible.

The tank breather valve isn't something I'm happy running without. Every time fuel sloshes forward, under braking or hill descents, this valve has got to stop overflows. If I remove the thing and reroute the breather line down, I'll end up dumping fuel either over hot stuff under the engine, or losing tank contents all over back country roads and rapidly running out of petrol.

I've spent a while thinking about this and the only solution really is to move away from contact seals. I had a play with a slider made from Teflon, deliberately not gas tight, but this weeps petrol and really won't work without catch bottles and roadside emptying of same. The slider also plugs gas flow so introduces a pressure gradient in either direction. After some thought, the only breather type that'll keep the tank connected to ambient pressure, with nothing in the way, is a type using floats and sinks, instead of spring loaded one way valves. I've got this on order:

https://www.rallynuts.com/motorsport-fuel-tank-vent-valves/mocal-in-line-fuel-vent-valve.html

We'll see how this works out.

[SVboy]

Hopefully this will be the root cause of your tuning issues.

[Ocean1]

The tank breather valve isn't something I'm happy running without. Every time fuel sloshes forward, under braking or hill descents, this valve has got to stop overflows. If I remove the thing and reroute the breather line down, I'll end up dumping fuel either over hot stuff under the engine, or losing tank contents all over back country roads and rapidly running out of petrol.

Is this really more of a problem than was/is the case with most dirt bikes, where the completely unrestricted breather tube runs down the steering head?

If so then you could look at some of the pneumatic silencers, either sintered bronze or plastic with holes so small they don't actually pass fluids at the sort of pressure differential you're talking about...

[OddDuck]

Is this really more of a problem than was/is the case with most dirt bikes, where the completely unrestricted breather tube runs down the steering head?

If so then you could look at some of the pneumatic silencers, either sintered bronze or plastic with holes so small they don't actually pass fluids at the sort of pressure differential you're talking about...

True. The quick low-tech fix is just run the breather line vertically upwards a distance, then down through the steering head and exit low and to the side. Should work 99% or more of the time. If the bike upends or falls over or similar then as long as the outlet of the breather is higher than the tank, it won't free flow petrol. Of course that depends which flank the bike ends up resting on... so the fix then is to zig zag it from one side to the other inside the fairing while making sure there's a minimum gradient on the line with the bike in normal position. Any petrol sloshing around has to drain back into the tank or out or else there's going to be airlocks.

The only references I could find to sintered bronze etc looked like they'd pass petrol as well as air. If I was going to go the way described above I think an inline filter would be a good idea - don't want dirt sucked into the tank... haven't met sintered that would pass air / vapour but not fuel yet though. I'm not having much luck googling, can you point me towards anything?

SVboy - thanks, fingers crossed!!

Anyway fantastic weather today, screw the imperfect running, got the bike out and went for a damn good fang out to Castlepoint. I'd nearly forgotten how good the 900SS is on that road. Had a great time.

Incidentally I noticed an unexpected bonus of the auxiliary headlights and running lights combo. It turns out that safety meets hooning on this one - drivers were letting me through much more than previous, particularly on the Hill. Less SMIDSY. More VROOM. Yes. It's been a good day.

[OddDuck]

The new tank breather valve arrived, I fabricated a bracket up to mount it, and have been trialling it over the last few weeks.

Short answer: it works but looks awful doing it. Next time I'm going with the flanged option, the one that requires drilling a hole in the top of the fuel tank. The outlet hose from that comes out at 90 degrees and so looks very close to the stock breathing arrangement.

The breather works by having two ball valves running vertically. Both seal on moving upwards, with the valve in a normal vertical orientation. One ball valve floats on fuel and seals on a rising fuel level - ie against slosh forward under heavy braking. The other ball is solid and sinks through fuel, thus sealing against the valve being upturned (ie the bike upside down in a ditch, at which point presumably I've got bigger problems than carb tuning). The rest of the time this breather valve is open, without any obstruction to gas flow forward or back.

AFR readings have settled right down. There's no longer any progressive moving to a lean condition under sustained back country running, or a rapid move to a super rich condition once getting to a built up area and 50 k zones.

[OddDuck]

I reckon I might finally have worked out what's been going on with the bike. Persistent oil fouling on the vertical cylinder's spark plug leading to rough running, misfires at low throttle, and general nastiness.

I took a good long hard look at this problem and came to the conclusion that there's a design flaw in the way that the vertical cylinder's inlet valve guide is installed. It's been pressed down into a pocket, at a shallow angle, and the stock valve guide seal is a simple rubber sock.

The guide, as made, is permanently sitting in a puddle of oil. This puddle, via surface tension and miniscus effect, is deep enough to reach up to the base of the rubber seal, keeping it permanently wet with oil. The seal isn't clamped on tight by a sprung metal band or similar - it's pure rubber tension, subject to engine operating temperatures and exposure to oil. In short the seal is not very tight on the guide. The rubber will flex under valve motion, effectively pumping oil from the puddle upward and inside the seal. Any wear on the valve guide or valve stem, and oil will be drawn under intake vacuum straight into the cylinder head.

The engine will work fine while stem and guide are new. Clearances will be tight enough to keep oil flow under control, with the seal sort of an optional bonus. The fun and games will start once there's a few K's on the bikes clock and things loosen up a bit.

I used a rag to soak up the puddle, then noticed that the puddle came back - several times. Interesting... it turned out that the guide seal was completely filled with oil. Voltaire's earlier comment about older opposed-twin BMW's came to mind: valve guides which are at high angles to the vertical, and which don't use seals at all and yet still work just fine. Looks like 'oil-splashed' is OK, 'oil-soaked' is not. I took a chance and carved drainage channels straight into the cylinder head.

To do this, I used a special centerstand to support the engine, then removed seat, rear shock, fuel tank, battery box and IDI's, then got in to the head with a Dremel and a ball nose burr. I deliberately did not use anything with particle abrasives. This was carried out with the engine still in the frame and took roughly six hours. Cylinder head drain channels were plugged with disposable earplugs threaded onto a knotted piece of high gauge wire, and the camshafts and rockers were wrapped with rags. I still ended up with fine aluminium shavings everywhere so swabbed the area thoroughly with cotton buds pre-soaked in PB Blaster.

Obviously this didn't protect perfectly or remove every trace of the carving work, there were still aluminium particles left... Perfect work would have required lifting the frame off the engine, taking the cylinder head off, and removing all internals including the camshaft prior to carving and washing. It's an old bike. Perfect left the building some time ago. I got nearly all of it and that's just going to have to do.

I've subsequently run the bike for a week, still on the same oil fouled plug. Results: an immediate improvement in running, plus the plug came out dry (for the first time ever) when I pulled it last night. The bike still isn't running perfectly but given the black enamelled coating all over the plug nose that's not really surprising. Looks like oil doesn't burn off over time. I've replaced the plug but haven't run with the new one yet.

A couple of comments after the week:

1) AFR gauges can be badly misled by oiled plug misfires. These will show up as an apparently lean or super lean mixture; the mixture might actually be correct but the non-ignition will leave lots of unburned O2 present in the exhaust.

2) These bikes are very sensitive to spark plug condition and ignition timing. Anything wrong with either of these will lead to rough running. It really doesn't take much of a deterioration in sparking to lead to weak ignition, delayed (and weakened) combustion, and a very rough motor.

The photos show exhaust and intake valves before and after, with a shot of the Dremel cutting setup for the intake. Care was taken in both cases to avoid having the burr hit the valve guide or its seal.

I'll run for a bit more with the new plug and see how that goes. In the meantime the plan is to get the bike to the next scheduled interval and change out oil plus filter and both plugs. The timing belts are due as well, it's been two years since the last set.

[OddDuck]

Have been having a play with the LED auxiliary lights setup. After a couple of rides I've been forced to rethink this arrangement - it's annoying the hell out of other road users (bikers included) and is producing glare off the road surface immediately in front of the bike. The glare is so bad that I found I was seeing more with the auxiliaries completely off, while riding the Rimutaka Hill on a moonless night. I was getting light flare off the visor, filling in shadows and completely losing detail in the middle / far distance... kind of important if looking more than fifteen meters ahead.

There's a couple of reasons for this. The first is the beam pattern: dip headlights have a squashed semi-circular or rectangular pattern, with light projected forward but not up, and most of the lumens going into the middle distance. The LED auxiliaries have a very simple parabolic reflector which throws a conical pattern of light forward. The only way to not dazzle oncoming road users is to point these things down. That means that the tarmac immediately in front of the bike gets most of the 900 lumens, at short distance.

The second reason that they're so obnoxious is the colour. These are very high-energy blue-white LEDs. They're very good at dazzling onlookers and leaving streaks across retinae but to my mind, surprisingly bad at lighting the road up so I can ride it. I'd heard somewhere that the human eye is best tuned to yellow-white (ie. sunlight), and after dark a slightly reddish yellow light is what we see best by in terms of judging distance and avoiding fatigue. Blue-white light is too stark: everything gets washed out and looks flat. The LEDs are bright enough alright. It's just that it's not right, at least for my eyes. After I'd turned the auxiliaries off, I found I was seeing easily with old-fashioned tungsten halogen, even with the 900SS's famously crappy front headlight.

There's also the legalities. Auxiliaries are OK if the main headlight/s are off... we're supposed to keep our mains on at all times, so legally speaking there isn't really the option there. Positioning lights along with mains are OK but aren't defined clearly. Small and not dazzly should be OK. Whatever passes muster with unsympathetic non-biker-friendly traffic cops, really... the original 4-light setup almost certainly wouldn't.

I've taken the big flank mounted auxiliaries off and changed the tint on the smaller positioning lights under the main headlamp. The tint (filtering) is worth going through: I was trying to change nasty blue-white into softer, friendlier yellow-gold, like the tungsten halogen main headlamp.

The photos show the mod. Some very cheap plastic folders from Warehouse Stationary provided the colour filters. The wad punch made cutting them easy. Installation was simple, just unscrew the lens or window on the front of the lamp, then try to put the filters in. After some experimentation I settled on three yellow, one pinky-red (magenta? or whatever the colour is) as a close-enough match to tungsten halogen. Something I found interesting was that if the plastic folders are laid on top of each other, the colour that comes out is an orange tint, very similar to the colour of an indicator lamp lens.

The reason for the mix of colour filters is maybe best shown by the colour wheel. If light of one colour - say deep blue - goes through a colour filter opposing blue, say an orange filter, most of the light will simply be filtered out. Very few light sources are purely one colour, there'll be a spectrum, so there's going to be some light in the green and the magenta, and that'll get through the orange filter. I found with just the yellow filters, the lamp turned whitish-green. Yuck. The folders aren't exactly pure yellow, they do have some green in their tint. The LED must put out something in the greens. The colour wheel shows magenta opposite the greens, so a weak filter around that colour is the way to get rid of it.

Comparison with the mains shows that it's pretty close. Another thing (which in this case is a plus) is that the plastic folders are definitely not optical material; they're diffuse instead of glass-transparent. They spread light out. This takes the edge off the lamps output very nicely and gives a nice soft uniform light ahead to complement the mains.

I've installed with the yellow layers closest to the lens, the single magenta closest to the LED. Once lit up the order won't matter; this is so that with the lamp off, it'll look yellow-ish rather than red.

[OddDuck]

Just some observations, jotted down before I forget... I've spent another (!) day attempting to tune the 900ss, with what might be progress, or might just be further tail-chasing. I'll start with some thoughts on Pat Burn's FCR Tuning Guide, as found here:

http://www.factorypro.com/tech/tech_tuning_procedures/tuning_FCR_Burns,Pat.html

Bear in mind that this is just me, I've got limited instrumentation (one AFR gauge, SOP dyno, plus plug chops) so this really could be just conjecture. But this is a specific version of the guide, aimed at the 900SS and anyone trying to use FCR41's with the bike.

Procedure:

0) Clean everything. There's no point in tuning against jets blocked with dirt.

1) float valve seats. The bike's 34 - 50 HP per cylinder / carbie, with pump-assisted low pressure gravity feed, so go with the 3.2mm seats. Check that these aren't floating loose in the carb bodies, you may have to use shim washers to set them in place tightly.

2) Float height. 9mm. Done.

3) Main fuel jet, main air jet. There are a few FAQ's, settings charts and forum posts out there so there are recipes to follow, alternately fit AFR gauge and go WOT somewhere legal and safe, or dyno. These affect everything so there's no point going further until you're confident with them.

4) Needle selection. Probably you'll be OK with the needles that came with the carbs but maybe you've modded airbox etc and need non-standard. Again, recipes off the web here are your friend, alternately further 1/4, 1/2, 3/4 throttle tuning with AFR and / or dyno. In order: base diameter, clip position, taper. L1 basically is clip position so when you run out of clips you'll need a different L1.

5) and here's where it starts getting painful, the below 1/4 throttle settings... start with slow air jets screws at 1 1/2 turns out, set idle speed to 1000 RPM or so, and try to get the idle mixture right.

This is worth further comment so I'll go into detail. Burn's guide discusses setting idle mixture by ear: you rev the engine and listen for rapid settling to stable RPM. If the idle speed hangs a few hundred RPM high before settling, it's lean, if it slows to below idle and then recovers, it's rich. Burns says to adjust for whatever gives you instant return to stable idle RPM on closing the throttle. AFR is a guide but not really reliable. Fine, except there might be a problem: the 900SS has unusually long and large diameter inlet manifolds.

There's a big problem with large fuel-air inlet manifolds: wetted surface area. Fuel will condense out of mixture onto the inside surface, or evaporate off again. That condensation / evaporation is dependent on air temperature, manifold temperature, and manifold absolute pressure (hence MAPs sensors in injected engines). Petrol evaporates more readily if it's in a high vacuum situation, ie near closed throttle. Open the throttle, fuel drops out of saturated vapor and condenses on the manifold walls. Close the throttle again and all the liquid on the manifold walls starts evaporating in a hurry. Since the manifolds have a large surface area compared to how much fuel the engine sips at idle, when the throttle is closed there's a temporary rich condition which persists for quite a few seconds. This is like briefly pulling a choke: the engine runs faster.

This might lead to a major difference in tuning compared to Burn's guide. Maybe you're better off tuning idle steady-state, ie reading against no-load AFR or plug chops. Transient behaviour when the throttle is closed might not be an accurate way to do this, and based on past experience I suspect that tuning for instant return to normal idle will give you an overly rich steady state idle mixture. It looked that way today; closing the throttle gave a brief richening of the mixture.

Anyway, what you're supposed to do next is to turn the Idle Mixture Screws in or out and then change slow fuel jets to suit. If the I.M.S. is less than one turn out from bottomed, you need leaner, so go a size down in the slow fuel jet. If the I.M.S. is more than two turns out, clearly there isn't enough fuel and so you need to go up a size in the slow fuel jet.

Yeah. I pulled the IMS screws and had a look at them... then had a play. There's four full turns of adjustment before the needle nose of the screw leaves the needle bore. The experience today was that the screws are still affecting mixture out to 3.5 turns, although the effect becomes more gradual as they go further out. I think the range of useful adjustment is much wider than 1 to 2 turns, I'm inclined to think it's more like 0.5 to around 3.

The other thing about the idle and slow jet circuit is that it handles emulsion, not liquid fuel. The slow air jet passage is aimed at the perforated base of the slow fuel jet. Air and fuel start mixing at this point, inside the body of the carburettor, not in the carb throat. Evaporation starts as early as possible. This might be the main reason why the carb bodies tend to run colder than ambient while in use.

The idle / slow circuit has two inlets to the carb throat: one behind the vacuum plate, ie on the high vacuum side - this is fed and controlled through the I.M.S. The other jet is between the front of the slide and the vacuum plate. It's hidden behind the main emulsion tube and needle and is only really visible from above with the slide removed. This is simply a fixed, drilled hole leading straight to the slow fuel jet and slow air jet, which are the only controls over the emulsion flowing through this opening.

The bike's had a problem with running super rich just off idle. Try as I might, I can't seem to tune it out, particularly on the vertical cylinder. I think this second circuit might be very abruptly providing emulsion once there's a slight opening of the throttle. That's guesswork, it's just not possible to see what's going on due to the jet's position. Anyway, this is why I've been taking the IMS out so far. Getting the mixture away from super rich at 1/16th through 1/8th means running a small slow fuel jet, but then I have to open the closed throttle fuelling right up to compensate, and / or tolerate lean or very lean idle.

And then...

6) recheck needle straight diameter and clip position. These play off against the slow air circuit between 1/8th and 1/4. There can be a lot of iteration back and forth.

7) no-load revving should sort out whether the slow air circuit is too rich or lean, adjust as necessary for high RPM and then re-iterate the slow fuel jet and IMS setting. And needle root diameter. Bah.

Oh, and 8) the cylinders will be different due to assymetric exhaust pulses. It isn't 360-360 timing, it's 270-450. The vertical gets a higher vacuum pulse than the horizontal. These pulses are quite strong in the 1/8th-ish region. Guess where most street riding happens... Oh, and the anti-rattle shims installed earlier seem to have made the carbs much more sensitive to this stuff too, mostly by ensuring that the vacuum plate actually seals properly instead of allowing air leakage due to bouncing around. THere's also a pretty good chance that there's fuel coming up past the needle as well due to a too-small root diameter, but there's not really any way to see this happening.

9) iterate. There's no way anyone gets this 100% on the first pass. Or the second, or...

Basically the below 1/4 stuff is a right PITA. No wonder people just say 'it's meant to be rough' and ride it.

[OddDuck]

A wee note about carburettor slide cutaways.

One tuning parameter is the cutaway; this affects the transition from the idle to the main circuits, ie the range just off the stops. In most throttles it's changeable by changing slides; the FCRs don't offer that option. There's one issued slide and that's it. At least I think so: it's stamped with 15, which would seem to indicate some kind of series. It's just that I haven't seen anyone offering these for sale.

The basic story is that more cutaway means a leaner mixture, just off throttle. I decided to give this a go since that off-idle rich transition is the bulk of my tuning problems. Doing this means very carefully, controllably, cutting more cutaway. Cut a little, test, cut a little more, test again. I'm taking 0.10 mm at a time, since it's kind of a one-shot deal. It's laborious.

It also seems to be working, in that the tuning spread has reduced from over 5 AFR points to around 2.5, with 0.4mm off so far.

The cutting method has to preserve the cutaway geometry and centering. It also has to be controllable and unlikely to catastrophically damage the slide, ie by biting in or flinging the thing. Not having access to a mill and all the goodies, what I've done has been to lathe up a cylindrical former of the same diameter as the slide cutaway, then use double-sided tape to hold some 400-grit wet'n'dry to the diameter. A bolt through the center and I'm good to fix this into my ultra-cheap drill press.

The drill press isn't being used in any sort of drilling or milling capacity. The cutter doesn't rotate. I'm using it as a vertical file. The wet'n'dry has been greased, in order to keep chips of silicone carbide under control. I don't want abrasives dropping over the slide and ending up in the vacuum plate / carburettor body interface - if that happens, they'll rapidly embed into aluminium and then rip the hell out of the coating on the vacuum plate.

A key part of this is measurement, being sure of the length I started at and where I've cut to. The verniers can very easily go off-square, hence the socket being used as a guide.

I'm unsure if this is helping. One thing I don't have is some sort of measuring device for vibration; I'm trying to sort out unacceptably rough running but it's purely by feel.

[pete376403]

You are a long way down the carburettor rabbit hole and the end may not yet be in sight. Have you considered fuel injection from an other-then-Ducati source? One such system I am on the process of building is Speeduino - an Arduino based system. check out F5 Daves thread on two-stroke EFI to gain an insight into the tuning capabilities of the hardware and software.

[OddDuck]

I'd had a thought: the flywheel attaches to the crankshaft not once but twice. There's a splined hub. The flywheel itself bolts to this via seven M6 cap screws, and is located by a pin. If this assembly had loosened after the main bearing failure, maybe that might explain some of what's been going on in terms of vibration and weird running issues. Only way to be sure was to drain the oil, pull the cover, and get in there to have a play.

The carrier / flywheel interface turned out to be fine. No play, no off-square, and the cap screws were in so tight that I reckon there's a chance the heads would shear if I tried to undo them.

What was interesting was noticing the damage on the inboard face of the alternator rotor.

The left had side of the crankshaft carries, in order from main bearing going outward: the half-speed drive to the timing belts shaft; a free-spinning one way clutch for the starter sprag, and inside that a roller bearing and cylindrical shoulder; the flywheel carrier and flywheel; the alternator rotor; and then the domed conical washer and alternator nut. There's a stack of components, in other words.

This spins at high speed and there's a lot of mass in the flywheel, which is roughly midway between the main bearing and the outboard bearing in the alternator cover. If it goes off center, there's vibration right there. Just to make life more fun, the crankshaft itself will be constantly flexing and twisting due to pistons being shoved around by combustion forces. It's not only simple whirling, like when the washing machine gets all the towels on one side of the drum. The crankshaft will be bowing one way and the other as pistons get shoved and then release, or go through TDC or BDC.

The stack, going over the outside of the crankshaft, greatly helps the rigidity of the assembly by being of larger diameter. This depends on everything being flat and square. If something's off, that rigidity can be compromised, or worse, the crankshaft could be bowed one way or another once the alternator nut is done up and the flywheel then set off-center right from the start.

I pulled most of the stack components and had a close look. Everything made out of steel looked alright but it turned out that the alternator rotor wasn't flat and settled on the flywheel, when I tried this on the bench. It'd rock slightly from side to side.

This does kind of follow. It's only purpose is to hold the permanent magnets for the alternator, in a non-magnetic material, so it's cast in soft aluminium. The crankshaft must have gone through severe flexing during the main bearing failure. The rotor was by far the softest item in the stack, so it got deformed.

The solution was to make an inner collet to hold it on a lathe, and then very carefully turn both outboard and inboard faces back to flat and square. I didn't have to take much material off (around 30 - 40 microns each side) to do this. Re-testing on the bench quickly confirmed that the rocking was gone, they sit properly together now.

As a note - for years I'd assumed that the half-circles of black material were some kind of magnetic material, or bonded rubber, so I'd left them alone. Nope. They're combustion ash, nothing more. They come straight out with a toothbrush.

As to testing... reassembled today, what seems to be a slight improvement, there's still some vibration there. The outboard bearing is a possibility. I'd got wrapped up in dealing with the rotor and had left it. I'll have to have a look with the engine running and the tiny cover removed and see if the shaft and bearing is steady or not.

[OddDuck]

You are a long way down the carburettor rabbit hole and the end may not yet be in sight. Have you considered fuel injection from an other-then-Ducati source? One such system I am on the process of building is Speeduino - an Arduino based system. check out F5 Daves thread on two-stroke EFI to gain an insight into the tuning capabilities of the hardware and software.

Yep agree. Am getting pretty tired... however (very slow) progress is happening...

One thing I was toying with was the idea of buying a donor injected 900SS and doing an engine transplant, looting the new bike for motor, shock, forks, ECU, injectors, throttle bodies etc. Apparently it's almost a straight swap in, some minor fabrication needed but nothing major.

The Speeduino idea is interesting, I'll have to read up.

[Voltaire]

I shelved my 39mm flat slides, nice bit of shelf bling.

[OddDuck]

Just a quick side note... as part of the current engine work, I ended up removing the pump cover. I have to take the clutch apart to do that, while rebuilding I decided to be fussy and clean everything, and I finally noticed something I should have seen earlier.

The stock clutch pressure plate, which has over 100,000 km's on it now, is covered in fine cracks. It's practically spiderwebbed. These normally hide from view under a coating of clutch dust.

I've taken a few closeup pics with a dedicated macro lens. These aren't all of the cracks visible, this is just the selection that seemed to photo best.

This has got me wondering if flex in the pressure plate is a big part of the reason that I've been having disengagement issues with both bikes. They're both running the stock clutch pressure plate. Both are fine (ish) when cold, then have problems with clunky clutches when warm. The 900SS is particularly bad but then it's got twice the mileage of the ST2.

Aluminium doesn't have a particularly high Modulus of Elasticity (the stress required to elastically deform the material, i.e. how springy or solid it is). Aluminium also has a rapid fall in stiffness with temperature, get it hot and it rapidly goes soft. I'd be very surprised if diecast Al-Zn alloy was better than normal alloy grades in terms of stiffness and strength, either at normal ambient or once hot. Throw in a lot of cracks in an apparently solid object and suddenly flex in the plate really could be an issue.

The cracks themselves are probably a mixture of as-diecast cracks and stress cracking from cyclic loading, vibration and heat / cool cycles. This component doesn't have an easy life. I can see why Ducati went with diecast alloy - like it or not everything is made to a price point - but why they had to go full weight saver on this when it's got a heavy steel clutch basket is a mystery. It's obvious that some engineer really did spend time on the design, bracing it, buttressing it, putting neat little stress relieving curves and fillets everywhere... but it's clearly made as thin as possible. Its weight is almost trivial next to the rest of the clutch pack, even with aluminium friction plates. There isn't much to be gained here by shaving a few grams.

At this point the plan is to replace both pressure plates, on both bikes, with something as stiff as possible and see how the change goes. The aftermarket has a lot of CNC machined plate aluminium options available at reasonable prices. The material's good, but I'm not so sure about the designs. They've generally tried to go as thin and light (or lighter) than Ducati OEM, while leaving sharp internal radii everywhere and machining visually interesting cutouts instead of keeping solid material. I'm tempted to have a go at machining my own, but the internal cogging necessary to mate to the clutch hub might be tricky.

[OddDuck]

A wee bit more work over the last few months... stripped the engine down (again) and had a very close look at everything. As part of that I found a head nut was loose. That particular stud anchor had failed earlier, I'd helicoiled a repair, and it had seemed fine on that earlier reassembly. It wasn't any more... The thread supporting the helicoil in the casting had completely torn out.

I'd drilled and tapped by hand. The stud hadn't been perfectly aligned. The under-tension part of the helicoil was only as long as the stud's threads, into soft casting alloy. It's possible that the helicoil had an issue with neighboring threads twisting relative to each other, since it's essentially a rolled-up spring. The thread profiles aren't particularly well defined.

I turned up a solid bung, internally and externally threaded, with a much longer engagement length than the helicoil. It's nothing fancy in terms of material, just some mild steel. That's deliberate. If anything in the chain fails, I want it to be this bung rather than the engine casing again.

The other part to the job was getting the relevant hole drilled on center and straight. I made a special tool for this, to guide both the drill and the tap. The idea is to transfer accuracy from the machine tool to the engine in its stand, then work from there.

[OddDuck]

A few pics of the rest of the job. The one-off tool was a pain to fabricate but the proof was in the reassembly... the head went straight on with no problems.

[OddDuck]

During the rebuild, I encountered a lot of trouble trying to correctly set preload on the main bearings.

Ducati engines use pre-loaded, rolling element, opposed taper main bearings. These engage on a nodular cast iron crankshaft, within aluminium alloy casings. Due to differences in thermal expansion between crankshaft and casings, some main bearing cold assembly preload is required. Once things warm up, the casings expand more than the crankshaft. These main bearings shouldn't open up once the engine is at operating temperature since there'll be impacting and skidding on the rolling elements and raceways.

Anyway, there's been a lot of debate over the years about what the best preload should be. Figures of anywhere between 0.3mm and 0.12mm (or even 0.05mm) are bandied around. I'm going with 0.15 to 0.18mm, after reading widely.

Setting this preload is a bit of a pain, you have to delete some shims from the crankshaft, reassemble loose, and work out free clearance using a dial gauge. You then throw in more shims to get the desired preload. Simple, if laborious... or is it?

Despite shimming it correctly according to the dial gauge method, I kept running into symptoms of over-loading. These symptoms were grindy main bearings and excessive out-of round on the tip of the crankshaft, where the alternator outrigger bearing runs. The crankshaft is squashed between the mains, there's compression across the big-end journal, so the crankshaft flexing because of this preload is plausible.

I'd checked the crankshaft for straightness earlier, btw. The between-centers method specified in the workshop manual is limited at best; I'd found it better to turn up some plain half-shell journals out of scrap aluminium for the bearing surfaces on the crankshaft ends, mount these half-shells on posts and a baseplate, and place a dial gauge on a free stand underneath the crankshaft to test all relevant surfaces. The crankshaft came in fine, within the 20 micron specification for maximum out of round anywhere.

So, what was going on with the preload?

After much time reassembling and testing, I finally realised that there's an issue with the cases behaving in a non-linear fashion, due to gasketing between the halves. When the cases nip up - particularly with old gasketing - they bow inwards. There's reasonably significant movement at center, on the main bearings, because of this flexing of the cases - approx 0.10mm, give or take. In a setting as fussy as mains preload, this is a real problem.

It happens because there's a centerline between casing bolts, and there's more gasket surface outside that centerline than inside it. The bolts crush the gasket off-center, so it then crushes more on one side than the other. Hence tilt between mating surfaces and dishing in the casings.

The photos are of the old gasket. The off-center nature of the sealing surface is clear, once you look for it, and there's clearly more crush on the gasket surface near the oil pressure relief - the closest part of the gasket to the center of the engine.

I think it's because of style. Yes, in an engine casing. Nobody wants to see knobbly bolts sitting outboard, so they're tucked in.

This is probably the reason that Ducati went to silicone gasketing such as Three-Bond. The problem evaporates once the casings engage directly, face to face. I've stayed with the gasket for this rebuild - I like the fact that PTFE impregnated paper will come apart again reasonably easily - so I've set the crush using the old gasket, then fitted the new gasket. They're the same type, torqued to the same specifications, so whatever behaviour the first had, the second should repeat it.

So far so good. Mains spin nicely and the alternator outrigger is out of round by roughly 50 microns, which isn't perfect but a significant improvement on the 120 microns observed when I went back into the engine to look for where the vibration was coming from.

[OddDuck]

Right, this is probably a bit left field... I've had a go at making my own main bearing shims.

This was done after noticing a few things about the crankshaft. Clearances between the crankshaft shoulder and main bearing inner races have opened up, particularly on the transmission side. The shim-locating flanks of the crankshaft are mirror-polished. There's what appears to be some sort of wear or cutting on the radius of the crankshaft shoulder, as if the shim has been working its way in there... and the inner diameter of the shims appears to be fairly shiny and smooth too.

This could happen if the crankshaft has been rolling within the inner race of the main bearing. This would happen on any open clearance between the two, I think, but would get progressively worse with wear and tear. The driver is the crankshaft being pushed one way and then another, relative to the bearing race (like pulling the piston down from TDC at the beginning of the compression stroke, then having the piston pushed into the crankshaft during the power stroke). Or it could happen if there's a constant push sideways, via the transmission gears. Certainly a lot of black oil had accumulated in this area when I took it apart. The crankshaft shoulders are polished, as well.

So, if there's relative oscillation and rotation happening (admittedly very small amplitude), then the shim/s find themselves caught between two elements (bearing inner race and crankshaft) which move relative to each other. So the shims move. They'd probably not want to stay on center, and there's nothing mechanical keeping them there in the original design.

If this happened (big if) then the shim edge could end up riding on the crankshaft's shoulder radius. This would increase shim preload, possibly by quite a bit, thus flexing the crankshaft and leading to out of balance behaviour on the flywheel. It wouldn't do anything good for main bearing lifetime, either.

Ducati appear to be aware of this. All engine designs from '99 onward use thick shims with a deep chamfer, which feature an inner diameter which will locate centrally on the crankshaft's bearing shoulder. Pre '99, though... it's thin shims, maybe stacks of them. On the alternator side, they're held by friction and the stack of components ending in the alternator rotor nut, which is torqued up to around 180 Nm. They're clamped pretty firmly at all times. On the transmission side, though, it's just whatever force is exerted by the engine cases, which will fall as the engine warms up while in use.

There's no positive radial retainment of the shims, in other words. There's no place where a diameter matches another diameter. They're just loose.

My idea was to make shims that located on a diameter, either crankshaft or bearing. In the end the best place was the outer diameter of the main bearing's inner race.

[OddDuck]

Carrying on...

Making these was a bit of an education in why commercial shims are flat discs, finished on a magnetic table surface grinder. It's just about the only way to do this in volume, to acceptable quality, in an acceptable time.

The method I used was just stupid hard work: lathe bar stock to size, send resulting blanks off for heat treatment, find that they come back buckled and warped, then flatten and re-diameter everything with whatever grinding facilities are to hand. Yep, had to spend a few hours trying to sort these out. In the end I tried to make up a rotating plate mount for emery paper, fittable to a tool post, and basically sand down to size in the lathe via passively driven orbital face sanding. There was a lot of trying stuff for size or measuring, while making sure that abrasives didn't go anywhere near anything sensitive. It got fiddly.

The material used was 4340 alloy steel, hardened and tempered to 42 Rockwell C (as per OEM shims). I never got there on the alternator shim. It simply warped too much to be corrected properly. Due to the hardening, it wouldn't spring flat either, so the thickness went badly out. The transmission side shim was useable, so that's in the engine now. I've had to use the original Ducati shims on the alternator side. As mentioned, this side is nipped up tight and should be OK.

A bit of basic learning happened on this one. Steel will expand slightly once hardened and tempered. There's a phase change in the material, resulting in a different blend of crystalline structures. The new structure is more rigid, hence the material gets harder. The expansion isn't predictable, or uniform: it depends on the material, the grain orientation and dispersal, the quench medium and how quenching was done, then the temper and cooling programme applied. Hence finishing to precise size via grinding becomes essential. There's little or no chance of keeping fussy precision worked into soft material prior to hardening. The precision just won't survive.

In the previous post, there are a couple of photos of the shims at various stages of work: as arrived back, bead blasted, then plain sanded against a surface plate, then orbital sanded in the lathe. That's the sequence I used, unfortunately the photos aren't in that order. If I'd had access to some sort of proper grinding machine I'd have used that.

The heat treatment company I used also bead blasted everything. I really hadn't expected that but it does make sense, given that the metal will get blackened and oxidised from being heated.

Grinding parallel planes really does want bonded grinding wheels, pumped coolant and magnetic work holding. I managed, via very laborious single-use workholding clamps and use of lots and lots of wet'n'dry paper, but there's no way I'm doing it this way twice.

Anyway, the transmission shim is in the engine now - the only way to be sure if this works is to use the motor.

[OddDuck]

Just a quick post for anyone else with a good shock but loose bushings.

The bushings themselves are an odd size: 12mm bore, 22mm OD, the shell is 9mm wide and the sphere is 11mm wide. The only aftermarket part I could find matching those sizes was an IKO spherical bushing part # SB12A, which has lubricant channels and requires regular servicing via greasegun.

Getting the old ones out is a bit of a chore, partly because it looks like they were never intended to be changed. The photos show the sequence.

1) 10mm collet type bearing puller is used as a punch, to drive the underside top hat down wards.

2) .. this gets the top hat just far enough outboard to get flat bladed screwdrivers underneath it, and lever it out the rest of the way.

3) 12mm pin punch drives the other top hat straight out.

4) Jeweller's screwdriver / s for the semicircular clips, these have to be lifted out of their grooves and then up and out.

5) a socket can be used to drive the bushing out, a proper press and lathed up press tool would be better here though. It's too easy to go sideways with a hammer.

6) a quick look at the groove I put in with a Dremel, earlier - greatly helps with getting the screwdriver blade underneath the semicircular clips.

[OddDuck]

Finally had a moment to carry on... at the moment the engine's back in the frame and the wheels, forks etc are back on, so the bike can be rolled around. Currently the job's stalled on the electrical system and deciding where I want to go with the bike's rebuild.

At the moment the (reduced) plan is to rebuild the bike relatively simply, using the original loom and instruments, but keeping the modifications of external conductor lines and relays for ignition and headlights. The original wiring isn't in good shape. This is not surprising after 25 years but I think it goes deeper than that... there are points in the loom which appear to be overloaded. Some of the crimp connectors have really gone rotten, yet connectors right next to them appear faded but still alright.

The loom construction is pretty simple: a length of wire with a crimp connector at each end, bundled and sleeved, with the assembly bundled into sleeving which is then held together with heat shrink. That's standard practice for just about every manufacturer. It's light, strong, and has worked just fine for nearly 20 years, well past the design life of the bike. It isn't amenable to being opened up for repairs though, not without a lot of reassembly work putting it back together. It's certainly possible to trim wire back at the free ends, so that's where I'll start.

The 30 amp rec-reg fuse holder has been a victim of change, I think. The fuse is a simple and very cheap piece of flat tinned copper, not the more modern Maxi blade type. I'm not even sure that it's possible to get fuses in this syle anymore and so it makes sense to sort out a replacement. Broken down in Eketahuna is a possibility, I need to go with what I can buy in Eketahuna. Or similar... it's a lot cheaper sorting out a fuse holder now than getting a tow truck later.

Replacing the 250 blade terminals won't be a problem. These are a standard automotive format and are widely available. Replacing the round crimp terminals used on some of the non-sealed connector blocks might be an issue, though. I had a scout online at Radiospares and Element 14 and rapidly became bewildered at the variety of connectors and crimp pins around. At the moment the best idea I've got is to take the loom into a local automotive supplies shop and show the guys behind the counter, maybe they'll recognise formats.

After the experience of dissecting the battery crimp terminals on the ST2, it's clear that I should replace these on the 900SS. They'll have opened up and oxidised inside the crimp joint by now. I also want to use some sort of brass commoning block on the battery terminals so that I can fit multiple eyelet connectors without creating a christmas tree.

[OddDuck]

I've spent the last couple of days trying to get the loom sorted out.

The simple part of that job is cutting off old, manky crimp connectors, stripping wire back a bit, and crimping new connectors. It's not perfect - the wire is discoloured under the insulation, at the new crimp joint - but hopefully it'll go for a while.

I've photographed the most rotten connector on the entire loom, the 6.3mm spade lug onto the input terminal of the ignition relay, and also sectioned that crimp joint. It's pretty clear that it's stuffed, outside and in. There's oxide through most of the wire bundle, and between the bundle itself and the crimp shell. In places inside the crimp joint the oxide isn't brown, it's gone green. Nasty. No wonder the ignition wasn't working properly before.

Something about the loom design on this particular bike is that Ducati chose to use the frame and front subframes as active grounds. On the original starter circuit, for example, the engine is grounded to the frame, then in another place, the frame is connected to the battery. The starter current has to negotiate two joints where tinned copper is bolted to plain steel. Steel rusts, and there are rust stains clearly visible on the connectors when they're taken off. It was brilliant when freshly connected, but rapidly degraded, with the bike hesitating to turn over when the starter button was pressed. It really isn't a very practical way to connect a low potential when there's a need to pass high current. With that in mind, I had a go at sorting out the starter cables, adding a direct connection between engine and battery, similar to the ST2's design. I might have noticed something while doing so...

The return path (ground) for the starter current is on the right hand crankcase half. The starter motor is bolted to the left hand crankcase half, with its ground through its casing. On starting, roughly 30 to 50 amps (can't be sure) is drawn. All of that amperage has to cross from the left half of the engine to the right, by anything connecting the two. So that's the crankcase bolts, all the gear shafts and selector fork shafts, the cylinder heads and their studs and nuts, oh and there was something else...

Yep: the main bearings.

This shouldn't be that big a deal, after all there's a lot of metal elsewhere to conduct this current, but there's also nothing preventing part of the current from going through the left hand main bearing, through the crankshaft, then through the right hand main bearing in turn. The bearings don't sit on insulators. They're on polished steel cups which are pressed straight into the crankcase halves, and ball bearings don't like having currents passed through them. In the meantime the crankcase halves are connected in lots of places, but none of them are particularly well defined as electrical conductors. There's a lot of oil, or gaskets, or silicone, or steel passivation in the way. If the crankcases have been apart and together a few times then the bolt threads will be in good contact. If the cases went together just once at the factory and stayed that way since then they might not be.

That said, obviously this works, I've got over 100,000 km out of the 900SS and I've put 25,000 km onto the ST2, but still... I've seen a few forum posts of Ducatis having mains failures at surprisingly low mileages. I don't know what percentage of the bikes this happens to. Maybe this is part of it.

I've gone ahead and found a place for the engine ground on the left hand crankcase cover. There's a 10mm thread left unused, just forward of the kickstand bracket bolts. It'll get covered in chain lube, but then again, it won't corrode... maybe this'll be OK. Quite likely I'm solving a problem that isn't that big a deal anyway, but we'll see.

[Laava]

I like that 3rd photo, cross section. It looks cleaner than it is but you can see what looks like a layer of bad patina on the inside of the crimp. So you are going to go ahead and completey rewire now?

[OddDuck]

Ideally I'd like to, but work / time / money to be put aside for a new ride for once / getting fed up with endless garage time / etc... kind of had enough at this point really.

For now I'll get the old loom going again at low current and fit bridge sub-looms for lights, accessories and ignition coils.

[OddDuck]

A bit more work tonight - finally got around to changing the oil filter before refilling the crankcase, and changed out the 6.3mm spade and blade connectors on the ignition switch connector.

The oil filter had bonded on good and proper with time, hence the abortive attempt to drive a screwdriver through and twist it off after the oil wrench simply popped off under load. Doesn't really work unfortunately... the filter wall is so soft that all that happens is that it opens up like a tin can. The design is sleek but... unfriendly to mechanics, if that makes sense? Ducati have gone for style and buried the filter into the crankcases. It's not possible to get a strap wrench onto this properly, although I've managed to grab the very end of the filter in the past. Didn't work with this one though... I finally resorted to drilling holes in the cup wrench and screwing it to the filter with self-tappers. This worked even after the damage done with the screwdriver.

The 6.3mm crimp connectors rate a mention: they're generic, they're simple, it's easy to repair a part of the old loom that has these. The copper under the insulation turned out to be nearly black with oxide, though. I've sanded it back as best as possible. It's pretty rough so it's anyone's guess how long this'll last.

[OddDuck]

Some more work... got the bridging relays mounted, finally. Took some thinking... I wanted to have roadside access if things went wrong, reasonably weatherproof, not interfering with anything else, not getting in the way of maintaining anything else, anti-vibration mounted, away from heat, and independently fused. In the end I found the front subframe just wasn't workable - too cluttered already - and anywhere under the tank was too busy as well. There's a peaked gap underneath the seat, between rider and pillion, and in the end it was the only real choice for keeping the layout clean.

The wiring is going to be a bit on the long side but that can't be helped. What I can do is make sure that the wiring is appropriately gauged for the electrical loading. I found a formula online courtesy of Redarc:

Voltage Drop = (Length x Current x 0.017) / Area

Length is in meters

Current is in Amps

Area is in mm2

This sort of thing becomes very important when wiring up vehicles like trucks and their trailers. Long path lengths, critical requirements for running lights. So after calculating, I'll need 2.5mm2 wire for the headlights. I'll use the same for the ignition coils connection to power supply, I want to keep resistance between coils and the battery as low as possible. I'm also keen on the idea of keeping 6.3mm crimp terminals into relays to a limit of no more than 10 amps.

I've mounted the little fusebox on a pair of wellnuts, separate from the bracket carrying the relays. This follows Ducati's mounting of the main fusebox, which has never presented problems. The relay bracket took a couple of goes to fabricate due to all the fiddly positioning. The basic idea is that it hinges on the two rubber grommets in front and bounces on the foam stick on strips attached to rear tray and seat underside. There isn't much in the way of side to side damping but hopefully this won't be necessary.

The last photo shows the start of the wiring being assembled. This will be sleeved, then the far ends cut to length and properly connected.

[OddDuck]

A bit more work... I've refitted the original loom, added a relay and connector eyelet mounting post at the front of the bike, for wiring in accessories easily, and got most of the way on the auxiliary / bridge wiring loom. I've also added a handle-bar mounted switch, intended for a pair of auxiliary running lights (I'm still sorting this out and will be for a while I think). Earlier I'd had a switch mounted inside one of the frame panels, which I don't recommend in a moving, riding situation.

I've made a fairly basic change to the original loom layout: it used the frame as a widespread earthing system. This is common practice on vehicles but I think there's a problem with it, at least on this bike: tin-plated copper connector lugs are bolted down to chromoly tubing with passivated or plated steel fasteners. The joints are usually exposed to air and also aren't watertight. There's a lot of room for slow corrosion, either galvanic or water / humidity based. Every one of the earths I've undone has turned out to have discoloured steel showing on the frame earth's surface and very dark surfaces on the terminal lugs. The change has been to add conductors tracing from the old connector directly back to a star ground arrangement on the battery terminal. The frame is still effectively grounded via the return starter cable connected to the engine, but now isn't used as a return path any more.

The best way to assemble bundles of conductors (for a motorcycle loom) is what the OEM looms do: high quality fabric based electrical tape, or PCV sleeving and heatshrink. The split, corrugated loom tubes available at Supercheap Auto, Jaycar etc are bulky and difficult to fit through the frame, especially if more than one has to go through a gap (yes I tried). I pulled the corrugated tube off again after I realised that it'd also trap water very easily. The PVC sleeving isn't available OTC to the general public, as far as I searched on a weekend of frustration (please let me know if there is a supply somewhere), in the end I had to order online through RadioSpares.

Assembling conductor bundles using PVC sleeving involves cable pulls. There are tools available for this but I found a budget garage solution: use hook ended welding rods (in a chain if necessary) and an aerosol lubricant called E-Z Cable Glide. Bearing grease or similar would also work but would get very messy very fast. This lubing has to be done because the conductors are almost always jacketed in PVC insulation and bind up inside the sleeve if pulled dry. I'd also found that having several sizes of sleeve was necessary and the size graduations between go / no go can be quite small - there was a big difference in practice between 8mm and 9mm sleeving, for example. Connector terminals have to be added after assembly and it's a good idea to leave enough spare conductor length that a terminal can be chopped off and replaced, at least once.

Packaging has been a problem. There really is only so much physical room for hardware and it's amazing how brackets, other components, covers etc suddenly get in the way when attempting to install wiring.

A general comment about looms... I understand now why aftermarket looms can cost near or over a thousand dollars. They're simply very high labour, very fiddly to make unless you've got some kind of jig and are doing a production run. Sourcing the proper connectors can also be very difficult. A lot of the gear used on this loom is Italian (of course) and from companies that aren't quite doing English and global yet.

[OddDuck]

I've replaced the clutch master cylinder with the same, a Brembo PS13 integral reservoir unit.

These are simple, reliable, cheap, basic masters which get the job done but little more... there's good reason for the upgraded units. The only adjustments possible are to tighten up the slack before acutation or to alter lever span. The integral reservoir will tend to foul on aftermarket adjustable clip-ons, as well.

The old unit was on the bike when I bought it and was almost certainly original; that means it had done 100,000 km without failure, but nothing lasts forever. Even though it was still working I'd decided to change it out as a preventative maintenance measure. Part of the reason for that was the second hand braided clutch hose I'd used with it, bought cheap off a crashed bike. That hose has always been a bit on the long side. Parts of the plastic cover were coming off and the hose had started to kink at the flex area around the headstock. If I was replacing the hose, it made sense to replace the master at the same time.

Being curious, I sectioned the old master to have a look at the internals. I'd assumed these were pop-together, permanent assembly, never come apart things: not true. It turns out that the core is held in by a tight-fitting rubber seal boot and friction. There isn't a snap-in retainer. It's pushed back into place every time the clutch is actuated, so that part of the design makes sense. Removal of the plunger is as simple as removing the clutch lever and then pulling the boot - and the piston underneath it - with a pair of long-nosed pliers. That gets access to the bore, so if there's a sludge buildup, it can be cleaned out. The large groove in the piston is for intake of fresh fluid, so this needs to be presented to the larger, off center hole in the reservoir at the lever-released end of the stroke.

There are a couple of issues with these masters. If the take-up slack adjustment screw on the lever is tightened too far, the cup seal on the end of the piston will never make it back far enough to clear and thus open the small fluid purge hole (middle of the reservoir). That means that the master can get into a situation where it won't release pressure. On the clutch that means a free revving engine and walkies, unless someone is savvy enough to back the lever's slack adjuster screw off. On the brake, well, it's terrifying. Hopefully the rider didn't squeeze the lever good and hard, because if this happens there's no letting that brake off again. Always leave just a bit of slack in the lever. It's possible to check for fluid being pushed out of the middle hole at the very start of the stroke, but this requires taking the lid off.

The second issue with the design is the nose cavity and its liability to trap air, just behind the banjo bolt. Once there's an air bubble in there, flow won't knock it out in either direction. It'll stay trapped until the master is taken off the bars, tipped to banjo-down vertical, and the lever flicked a few times.

Bleeding can be a problem if there's significant air volume in the system, especially if the air is up high near the bars. I had to use a syringe to pull fresh fluid through the bleed nipple for the initial fill, and then do that again after there was a problem with the copper washers on the hose at the master cylinder and partial draining and disassembly was needed.

Sectioning was done by hacksaw, file, and finally wet'n'dry on a plate. The piston looks brand new. There's some polishing in the bore - no scoring or visible ovalling of the bore - and some gunk at the nose of the piston. I can't be sure of the cup seal's condition, but can say that it isn't replaceable. It's behind a top hat washer which has been riveted on. The low pressure sealing O-ring is showing some polishing where the piston worked back and forth, but hasn't swollen, set, or perished. They're pretty well built units, for what they are.

Note that in the partial assembly section photos below, I've left the spring out - it was the only way to get everything to sit in place properly. Normally the spring sits onto the top hat and against the far end of the inner bore.

[Kickaha]

Being curious, I sectioned the old master to have a look at the internals. I'd assumed these were pop-together, permanent assembly, never come apart things:

The second issue with the design is the nose cavity and its liability to trap air, just behind the banjo bolt. Once there's an air bubble in there, flow won't knock it out in either direction. It'll stay trapped until the master is taken off the bars, tipped to banjo-down vertical, and the lever flicked a few times.



You can get rebuild kits for just about anything Brembo

Second issue you can fit a banjo bolt with bleeder, although cracking the bolt to bleed it works

[sidecar bob]

The second issue with the design is the nose cavity and its liability to trap air, just behind the banjo bolt. Once there's an air bubble in there, flow won't knock it out in either direction. It'll stay trapped until the master is taken off the bars, tipped to banjo-down vertical, and the lever flicked a few times.


Correct. Bolting the master cylinder firmly to the handlebar should be the very last step in bleeding brakes, in fact 90% of the air will naturally come to the top given a little patience & holding the master cylinder on an angle is the best way to achieve that.
I have a short section of handlebar that I bolt master cylinders to, so I can achieve the required angle.
It usually results in less than a tablespoon of wasted fluid.

[OddDuck]

While carrying on with the rebuild, I noticed that one of the old plugs has a faint brown line on the insulator, ending at where the spark plug boot starts.

It looked a wee bit like an arc path, like high voltage has been tracking across the insulator and leaving a trail. There will be some combustion gas blow-by due to differential expansions in the plug body, if the plug has enough k's on it, but there was also something silvery-grey over the insulator. All plug nose insulators were fouled and they haven't been run all that long. I had a look inside the plug boots and found a mess.

These are the older style that have a spring loaded brass socket which pushes on to the threaded end of the spark plug - the bead at the end has be unscrewed and discarded for these boots. They've had a lot of plugs through them over the years and it looks like particles of brass have been coming off and getting stuck onto the inside walls.

There's a very clear carbon arc path shown in the photos, plus a few fainter lines visible. They look like someone's been doodling with a pencil. I've been losing significant amounts of spark to this, possibly for some time, and it was like this on both boots. A quick turn with some bits of 360-grit paper, held on a rubber tube serving as a mandrel, cleaned up both boots without too much fuss. The plastic looks alright, if no longer glossy. I haven't attempted an engine start yet though.

[OddDuck]

Finally got there. The bike's going again, vibration sorted.

Multiple causes...

Ancient hose clamps between carburettors and inlet manifolds which had worn smooth on screw and band, these just didn't stay tight. At first I tried improvising wire clips to lock the slotted heads on the drives but finally gave up and bought the proper (improved) replacements.

Rotten wiring and tarnished connectors on the low tension side of the ignition. The grounds for the ignition modules really weren't the best, and the brass crimp connectors were shot too. I found that the same part was used on a Monster so ordered these and replaced the wiring completely with something thicker.

Misaligned inlet manifolds. They can be moved around a bit on their cylinder heads; this can mean they're too wide or too narrow on the parallel carburettors and the rubber heat mounts can be made to flex a bit far as a result. Simple enough to sort out.

Gunking in the carburettors themselves. Well, this is embarrassing... of course this is going to happen if the bike's laid up for weeks at a time and only run briefly. Gotta put a couple of tanks of petrol through it before making any calls about fuelling.

Loose engine mounting bolt. There are only two of these, both very long M10's, and a tight couple to the mass of the frame helps to smooth out any engine vibration. I found the rear bolt had lost most of its torque - reassembly this time was with Loctite 222.

The biggie was an imbalance in the stock flywheel. I finally put a dial gauge onto the flywheel to check runout and presto, yes this'd explain the shuddering and why it's particularly nasty on the left footpeg. It was showing a runout of 120 microns, aligned with the induction trigger. This increased to 170 microns on a re-fit, i.e. 85 microns off-center. There was some free play in the flywheel mounting spline. Rotating the flywheel mounting position by approx 180 degrees almost cancelled the runout; this would seem to indicate that the off center is present on both the crankshaft and the flywheel. High mileage bike, earlier mains bearing failure, mid-90's Ducati in serious financial trouble, etc etc... it's plausible.

A quick look at the Wikipedia page about balancing gave me a couple of simple calculations:

U (unbalance) = mass x radius
Force (unbalance) = U x w.w (where w is rotational speed in radians)

Lots of measurements of the crankshaft's component stack with dial gauge, vernier calipers, digital kitchen scales, and then lots of careful adding up of U terms, and I had a possible solution: slightly enlarge the hole drilled through the flywheel already. It looks like Ducati drilled this hole at the factory to compensate for the induction trigger on the flywheel rim. If the entire flywheel moves ever so slightly in the direction of the trigger, leading to out of balance, then enlarging that hole shifts the center of mass back to the crankshaft axis. It's possible to work out how much mass is removed via density of steel and calculated volume prior to machining.

So I took the flywheel off, put a drill of the calculated size through the hole using a drill press, and remounted it on the carrier. It appears to have worked. The bike (after a couple more fuelling tweaks) is running better than it has at any time since the mains bearing failure.

It's a dicey procedure but a) it was just the flywheel and b) it's an old, high mileage, fun but not particularly special bike which is not and never will be a 916 or similar. I was OK with taking the risk. Something newer and nicer... for once I'd pay a pro, mostly for the peace of mind.

The bike's done several all-day rides since reassembly and appears to be going just fine.

[Bonez]

Good to see you got things sorted out with the old gal oddduck.

I found carb/injecter cleaner mixed with fresh tank of feul, Supercheap had the same brand on special recently for around $7 instead of the usual $17. Did a return trip tfrom Palmy-Havelock North and my Suzuki XN650 was running as if it was a totally different motorcycle. Much smoother and no random cutting out,

[ruaphu]

Bloody outstanding work, have enjoyed every single word and photo of this marathon. Nice to see ya finally get a win a d fingers crossed some long term reliability too [emoji106].


Sent from my iPhone using Tapatalk