Winter Layup - 1995 Ducati 900 Supersport

[Ocean1]

I couldn't quite get the very last stud.

http://tradetools.co.nz/products/2850100

Blow the 556 out with the compressed air, warm the area, spray the PB blaster around the stud root and leave it a couple hrs.

Also, whereas usually an impact driver would be the go, over that length it'll be less effective. A bunch of light smacks on top of those nuts with a half pound steel hammer would probably help though.

Oh, and if you're going to put stainless nuts on stainless studs use a liberal fingerfull of high nickel anti-seize paste on the thread.

[OddDuck]

Thanks Ocean1. Forgot to mention, I have been using the hammer on the stud ends before attempting to undo - solid taps, nothing harder. The idea (I think) is to break any metal oxide welds, where screw has been corroding into housing. Hasn't been a problem on these though.

The stainless steel nuts are just being used on high chrome studs for loosening, they're not going on for reassembly. Like tends to grip like and this is useful for the poor man's stud puller, this is about the only time that stuff with a tendency to cold weld together is actually a good thing.

The last one - I don't think it's all that big a drama, it's just that it needs more torque than I can transmit through two nuts tightened against each other. Might be time to stop being cheap and get the proper mechanic's stud pullers, there have been enough times over the years that M6 / M8 / M10 studs have been needing to be changed.

That PB Blaster stuff looks the business, thanks for the link!

[Ocean1]

That PB Blaster stuff looks the business, thanks for the link!

One of the very few "new, improved" magic potions that mostly do what they say on the can.

[pete376403]

I have had pretty good success with this type of stud extractor http://www.trademe.co.nz/building-re...1090635120.htm (only referencing this for the picture, not this particular item)

[OddDuck]

Got onto Trade Tools and ordered the PB Blaster this morning, plus one of the Facom 10mm stud pullers (same design as your link Pete). Not cheap - $85 for one - but I know the brand and I reckon that this is one of the jobs to get done right. Bucks up front hurts, but it hurts less than big bucks later if I screw it up.

No disassembly tonight, instead I'm chasing one of several ideas that I've been playing with for a while. I want to run a few calculations about the way that the bike works.

Surprise result from earlier: 70% of the heat conducted to the inlet stub pipes comes through the pair of M8 mounting studs. Only about 30% goes through the 0.4mm paper washer, despite the relatively massive surface area. I want to get that inlet temperature down, so insulating top hat washers are on the to-do list, along with before and after measurements.

Tonight was about checking inlet pipe and airbox volume, via (I really hope there's a proper word for this technique) filling them with water and then pouring out into a measuring cup, via a bucket and in stages if necessary. I sealed up with masking tape and whatever was to hand, it only had to hold water for a few seconds.

Results:

Inlet stub pipe: 37mm diameter, 160mm path length (approximately), 150 mL internal volume.

Airbox lid: 1.7 litres

Airbox body: 4.1 litres

I'd briefly checked parts lists earlier and found that the inlet pipes seem to be unique to the 900cc motor. The 600cc version uses a different part, indicating that these may be a tuned item. The airbox is common to the two bikes though.

Total airbox volume is around 6 litres (allowing for the spacing effect of the filter), and is a simple through-flow design. Extra volume is packed in wherever space was available. It doesn't seem to be explicitly intended as a tuned resonator, but I'll have to run the numbers and double-check.

One effect I'm keeping in mind is that the two cylinder intakes are right next to each other. A 360 degree parallel twin would have equal induction timings and would balance air demand out between them; a 90 degree V twin has a 270 - 450 degree induction timing. Air takes time to refill a low pressure zone. One cylinder gets nearly twice the air recovery time of the other.

[OddDuck]

Spent too much time over the last three weeks weighing up what I'm going to do with the frame. I want this cracking problem sorted out.

The best way to do that is to close the upper triangle (that's why the airbox stuff above), and for that I need to weld a cross tube in. So: what's the tube to be made of? Obviously it should match the frame.

I did a lot of googling - what exactly is a mid-90's supersport frame made of - and the short answer is that nobody outside the factory knows for sure. There's some chatter on the boards but about the most conclusive answer was a brochure which alleged a steel containing chromium and molybdenum (but it didn't specify alloy grade or percentages), and commentary from repairers stating that it hacksawed and bent a lot easier than 4130 chro-mo.

Not exactly conclusive.

Work has some cool gear. One of these items is a scanning electron microscope. This unit has the ability to examine what's actually in a sample, that is, atomic elements present by number or weight percentage. A correctly prepared sample can then be interrogated so the user can find out exactly what alloy it is.

I cut as tiny a sample as possible off the frame, at the end of the short tubes which carry the passenger portion of the seat. This was then sanded to take the paint off, ultrasonically washed in lab ethanol and tested.

The results are a bit dicey. The paint didn't come off cleanly, or it bonded with the paper and then smeared over the surface again. The microscope only interrogates to 1 micron depth. Any contaminants on the surface will skew results. So, bearing that in mind, here's what I got:

C (carbon) 3.0 to 3.9 %
O (oxygen) 1.7 to 1.8 %
Al (aluminium) 0.7 to 0.6 %
Si (silicon) 0.4 to 0 %, possibly from the silicon carbide paper
Mn (manganese) 0.5 to 0.6 %
Fe (iron) 93.7 to 93.2 %

A third scan, of an unsanded groove, showed massive amounts of C, O, Ba, as well as Ti, Ca, S, Mg, and Si and Al - it made a good control check against what must be the paint base layer.

So I think that the frame is a plain, simple, low to medium carbon steel - one of the 1000-series alloys. I can't be sure which one, a better prepared and properly cleaned sample would be needed for that, but any half-decent low carbon steel should do fine for the reinforcement tube.

[Voltaire]

Thats pretty interesting and in line with my Engineer mate who when modifying his SS frame to make an F1 replica described the tube as the same as what they make school chairs out of.. and the welding is not that great either.
I was playing around with a BMW frame a few years ago and bought some 4130 chro-mo from Palmly (?), and its much harder to cut and bend than mild steel tube.
Your right about the Google search on cracked frames, lots of them out there.

I took a photo of the carb/air cleaner set up on mine.Its got FCR's ( came with them)
I'm not sure of the role of air boxes as none of my old bikes have them, are they sort of a buffer/damper for CV carbs?

[OddDuck]

Thats pretty interesting and in line with my Engineer mate who when modifying his SS frame to make an F1 replica described the tube as the same as what they make school chairs out of.. and the welding is not that great either.
I was playing around with a BMW frame a few years ago and bought some 4130 chro-mo from Palmly (?), and its much harder to cut and bend than mild steel tube.
Your right about the Google search on cracked frames, lots of them out there.

I took a photo of the carb/air cleaner set up on mine.Its got FCR's ( came with them)
I'm not sure of the role of air boxes as none of my old bikes have them, are they sort of a buffer/damper for CV carbs?

OK, that photo shows the remains of the original airbox still in place, the coil mountings and battery box are integral with the airbox mouldings.

Airbox serves as:

Intake noise muffler
Weather shield
Reservoir of air
Resonant cavity (check Helmholtz resonators)

The resonance is useful because (according to my reading) any engine with valve overlap (that'd be almost all of them these days) will have a glitch in the midrange somewhere. The airbox is usually tuned to resonate at that RPM and help smooth it out.

[OddDuck]

Got the last cylinder head stud!

PB Blaster, a heatshrink gun, and the stud puller cracked the thing. Didn't take all that much heat to do it either - I took the stud to just over 100. As the thermal camera shows it's always going to get hotter than the casing. This was the only stud with traces of threadlock still present.

The stud puller turned out to be a one-shot kind of tool in the end, after a few applications it tends to chew the threads up and then come off the stud suddenly. Not really the best, and I had to finish the job with the nuts tightened against each other. Got there without ripping any threads out though.

[OddDuck]

Carrying on with airbox / engine breathing musings... having a look at ram air effect in the inlet pipes.

Total length from inlet trumpet (inside the airbox) to inlet valve is 367 mm / 14 inches.

That indicates maximum ram obtained at around 6,800 RPM, for a system with no airbox.

With the airbox things change a bit. From http://www.calsci.com/motorcycleinfo/Airboxes.html, the usual story is an airbox with a snorkel acting as a resonant system.

Ignoring the inlets to the engine, the air in the snorkel is like a mass free to travel back and forth, and the airbox a spring. There'll be a frequency that they want to bounce at.

The snorkels are a pair of very short, stubby rubber pipes, with a flanged end angled at 45 degrees. Taking the median length: 6 cm
Diameter: 3 cm
Area: 7 cm2 per pipe, total is 14 cm2
Airbox volume: 6000 cc

From the page above:

resonant rpm = 9550 sqrt( 116.5 A / VL ) (V-twin) = 9550 x sqrt ( 116.5 x 14 / ( 6000 x 6) )

= 2000 RPM.

Hmm. That might actually be believable on a streetbike, given that V-twins are notorious for being gutless at low revs. Ducati's design engineers might have tuned the box to give the motor as much help as possible down in the low revs. They were obviously constrained for space to the sides and around the carburetors, but there's a lot of volume up front and low to make up for that.

Not much changed when I ran without the snorkels, or after I cut most of the airbox lid out (as per the FCR41 fitting instructions), but that might be due to the fuel tank now forming the resonator lid, and the flow path between tank and airbox now forming the inlet pipe. Equally it might be that the airbox itself simply isn't that good a resonator. It's a weird shape, there's a filter in the middle of it, and it's made of sound absorbing plastic.

Compare that to Helmholz' original resonator, made to pick out individual notes in a mass of music, which is metal, spherical, and clear volume inside. Quite different.

So for me it's not a stretch to believe that it complies with theory, but in practice falls short of ideal behaviour.

[Voltaire]

Interesting about the air box, I thought it was just to mount the air cleaner on
I've been playing around with my 1972 (ish) BMW racebike for a few years and after fitting a new cam at Xmas took it out for a dyno run.
Had a massive dip in power at about 3500 to 4500, pretty much the pull out of corners range.
Ran it at Pukekohe in Feb and had to battle bloody 650/750 Triumphs out of corners
My German Guru told me to reduce the diameter of the exhaust and fit the merger at a specific length.
I can't say I thought it would make much difference but picked up nearly 20HP in the mid to upper range to the amazement of both myself and Dyno guy. The $100 spent on exhaust pipe was well spent.
German Guru alluded to the next thing looking at the 60mm trumpets I have on the Dellortos as he said they are too short and open up too much.

Maybe you weld in the bracing on the frame and make up a custom air box that might need to be in a few pieces to fit.
Got me wondering about my FCR's with foam filters only.

Dyno chart for BMW. After finding a local Dyno I am now a convert.

[pete376403]

Got the last cylinder head stud!

The stud puller turned out to be a one-shot kind of tool in the end, after a few applications it tends to chew the threads up and then come off the stud suddenly. Not really the best, and I had to finish the job with the nuts tightened against each other. Got there without ripping any threads out though.

Did you have the stud extractor only on the threads? Looks like it from the way the threads are flattened out - I'm sure it would have worked better n the unthreaded portion of the stud.

[OddDuck]

A new airbox design was on the cards as soon as I realised that bracing the frame properly meant modding or completely rebuilding the stock airbox - well spotted

That's both a problem and an opportunity. Yeah, it's big work. But, what if (properly designed) I could keep existing performance and then improve it?

The stock Ducati setup is notorious for running out of puff early. Redline is at 9000 RPM, but there's no point whatever in going there. Torque peaks at about 5,500 RPM, power at about 6,500 RPM, and then falls off rapidly. Obviously the not-very-straight cylinder porting and two valves per cylinder has a lot to do with that, so does valve timing, but some of it has to be the intake system.

So: the intake is under the tank, in the middle of the bike's stagnation zone. The stagnation zone is the area behind the fairing, or the engine, or anywhere out of the slipstream. There's a very popular idea that a shielded air intake should be here, because this is the region of highest static pressure... I think that this may be a mistake, for modern bikes. I don't think the theory is wrong. It's just that carburettors used to be pointed backwards, presumably to avoid ingesting stones and so on, and if they were out in the slipstream then they were working against it. Filters came next, then airboxes, but the basic idea was the same: put the intake in the stagnation zone.

The equation itself is:

0.5 x density x velocity squared + density x gravitational acceleration x height change + absolute pressure = a constant.

It's true only along a streamline. You can't jump from one streamline to another and apply it. Change in height in this situation is miniscule, so it simplifies to:

0.5 x density x velocity squared + absolute pressure = a constant.

So, if you have a bike tearing along at a nice legal 100 kmph, which is 27.8 m / s, and it's an ideal world of perfectly still air, what happens is -

Air with no velocity and normal atmospheric pressure is picked up within the confines of the bike's fairing / rider / tank / engine, and accelerated to 100 kmph (on average) before being inducted by the engine. Some will be inducted from the front, some from the sides, some from the rear, so velocities will vary, but the average will match the speed of the bike. These all happen along their individual streamlines, so generally:

Static pressure plus no velocity = a constant = whatever the new static pressure is, plus a velocity term. The new static pressure (the induction pressure) is atmospheric pressure minus the velocity term.

So the pressure in the induction zone actually falls below atmospheric, and this effect gets worse the faster you go. The numbers come out to:

100 km/h: -464 mPa
150 km/h: -1043 mPa
200 km/h: -1,855 mPa

Sounds dire but the 200 km/h result is about 1.8% of normal atmospheric pressure.

Interestingly, if you apply the same theory the other way - to the pressure buildup in ram induction pipes - if no air is drawn from them, the pressure difference goes the other way. You get the same numbers as above, but they're positive.

So, what's the air demand from the engine?

900cc, at

1000 RPM: 7.5 litres per second
3000 RPM: 22.5 litres per second
6000 RPM: 45 litres per second
9000 RPM: 67.5 litres per second

That's assuming 100% volumetric efficiency at all engine speeds, which simply won't happen, but all the same it's a lot of air that the engine is trying to gulp its way through.

I worked out what diameter ram intake would be needed for this kind of air supply, with air scooped up nicely, for 6000 RPM at 200 km/h. It came out to 45.4 mm. That's with no change in air velocity - it goes into that air duct at the exact speed of the bike. If you want a pressure increase, you have to make the duct bigger in diameter.

I then ran the numbers for a resonant airbox again, using the formula in the earlier post. To get around the 270-450 induction timing problem, I assumed a pair of airboxes, one for each cylinder. If the inlet pipe is 45mm diameter (for each, effectively doubling what I've got above), and I manage a 3000cc airbox, the inlet pipe length works out at 3.54 cm.

2 litre airbox, 45 mm inlet diameter, 2000 RPM resonance (for single cylinder engine): 53 mm inlet length.

The Mach number for the above situation is 0.16. With the OEM Ducati snorkels, I worked it out at 0.187. Neither is particularly high, but the lower the better.

An alternative to the pair of singles (probably better) is to re-do the stock airbox, shared, of 6 L capacity, but with large diameter ram air intake tubes sealed to the box front, and resonant pipes within those going through the box front wall. There'll be plenty of room under the tank for extra volume and I'll be able to use the standard filter.

So I think it's actually possible to build this.

[OddDuck]

Did you have the stud extractor only on the threads? Looks like it from the way the threads are flattened out - I'm sure it would have worked better n the unthreaded portion of the stud.

Absolutely, but the shank of the stud is 8mm - too small for the extractor to grip. It'd only go onto the 10mm threads.

[OddDuck]

More work today, getting ready for the casings split.

Starter motor is held on by three cap screws, two of them inside the alternator cover, and one of those hidden by the starter relay gear. Rotate the gear to the right place and there's a hole in the gear's web to allow access to the cap screw beneath.

These screws turned out to be a lot looser than they were when I refitted the starter, about six months ago. The washer I'd cut from generic 0.4 mm gasket material was shot, too. It's dark in the photo, with engine oil and ash having made it right through the seal interface. On the rebuild it'll be worth finding one of the green OEM gaskets. It's probably also worth using plain steel spring washers on the cap screws. I don't want these coming loose again, since aside from holding the motor on, they are the electrical connection from starter motor to ground.

I was careful with unscrewing the starter motor lead (using the vice on the spade lug, to keep strain off the motor itself) because a while ago I'd replaced the brushes. While doing that I'd found that the M6 post for the 12V line is supported by a Bakelite insulator. It's not very tough and it doesn't take much to break bits off it. The rubber boot tends to trap water, so the M6 nuts on the lead rust into place, and a lot of torque is needed if you're working with the motor still attached to the engine... it really isn't the best design in the world.

The pickup coils came out next. First thing is getting the leads out of their plastic box headers, so the cable can pass through the gland in the engine wall. This was actually pretty easy - Ducati have a special tool for getting the crimp terminals out of their housings, but one of the smaller flathead jeweller's screwdrivers will work just fine. There's a spring tab locking the crimp terminals in place. Find it, press it, they pull out. After that it's just a matter of undoing the two mounting nuts (keep these, they appear to be a special item) and then removing the lot. Coil resistances tested fine.

Ducati have a special tool for locking the alternator rotor, too. Didn't have it, didn't need it - a strap oil filter wrench (diameter approx 76mm) and an impact wrench took it straight off. There's supposed to be a safety washer there, I just found a flange nut and plain washer. After that the rotor and then the flywheel, complete with one-way bearing and gearwheel to starter motor intermediate shaft, just pulled off.