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Thread: Winter Layup - 1995 Ducati 900 Supersport

  1. #661
    Join Date
    28th January 2015 - 16:17
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    2000 Ducati ST2
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    Lower Hutt
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    replacement of a failed Helicoil

    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.
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  2. #662
    Join Date
    28th January 2015 - 16:17
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    2000 Ducati ST2
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    Lower Hutt
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    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.
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  3. #663
    Join Date
    28th January 2015 - 16:17
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    2000 Ducati ST2
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    Lower Hutt
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    gasket crush issue with Ducati engines

    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.
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  4. #664
    Join Date
    28th January 2015 - 16:17
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    2000 Ducati ST2
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    Lower Hutt
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    Main bearing shims 1

    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.
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  5. #665
    Join Date
    28th January 2015 - 16:17
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    2000 Ducati ST2
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    Lower Hutt
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    Main bearing shims 2

    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.
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  6. #666
    Join Date
    28th January 2015 - 16:17
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    2000 Ducati ST2
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    Lower Hutt
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    Removing rear shock spherical bushings

    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.
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    Last edited by OddDuck; 10th December 2019 at 19:34.

  7. #667
    Join Date
    28th January 2015 - 16:17
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    2000 Ducati ST2
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    Lower Hutt
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    rotten old wiring

    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.
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  8. #668
    Join Date
    28th January 2015 - 16:17
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    2000 Ducati ST2
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    Lower Hutt
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    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.
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  9. #669
    Join Date
    3rd October 2006 - 21:21
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    Breaking rocks
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    in the hot sun
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    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?
    Only a Rat can win a Rat Race!

  10. #670
    Join Date
    28th January 2015 - 16:17
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    2000 Ducati ST2
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    Lower Hutt
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    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.

  11. #671
    Join Date
    28th January 2015 - 16:17
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    2000 Ducati ST2
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    Lower Hutt
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    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.
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  12. #672
    Join Date
    28th January 2015 - 16:17
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    2000 Ducati ST2
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    Lower Hutt
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    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.
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