175 TS Narrowcase Crankshaft Shimming Advice

[Samurai]

Hi Guys,

Although I've owned and worked on belt-drive Ducati's for years, this is the first bevel-drive one I've owned and I'm after some advice from the gurus on this wonderful site!

I've completely stripped the engine, replaced all the bearings with those supplied by Nigel Lacey Ducati, had the crankshaft checked/rebuilt and a cylinder rebore done by Ducati single's specialist Brian Silver (Motomarianna), both here in the UK. The corner has now been turned and I'm finally starting to put bits together, rather than taking them apart!

I'm aware that the most important thing is to get the crank shimmed correctly as all the subsequent bevel shimming relies on that. Brian Silver did give me a few tips on how to start, like grease one side of the centre gasket (to make sure it doesn't stick when you subsequently take it apart to adjust the simming for the umpteenth time) and to ensure that you leave the cases correctly torqued down overnight to allow the gasket to fully compress.

However, something basic I forget to ask was, do I need to do all this with the transmission gears in place? Does this have an effect on how tightly the cases will join and therefore the crank shimming, or am I thinking too deeply about this?

From what else I've managed to glean from other posts, I'm aiming for zero play in the crankshaft, whilst still allowing the crank to spin freely without any hint of binding, is this correct?

I'm aiming to fulfil a life-time ambition of riding in the Moto Giro d'Italia, probably in 2018 (when he bike's finished, bedded in and I've saved up enough!), so I'm keen to take my time and ensure that everythings done correctly and reduce the chances of any mechanical misfortunes during the event. Therefore any advice on the crank shimming or any other aspect of the engine rebuild that I need to be particularly aware of, would be gratefully received.

[Jordan]

That is how I have done it.
Rationale is that, as aluminium alloy expands with temperature at a greater rate than steel, then it will never be too tight in service if end play is set at zero.
Negative clearance could be arranged too, but I've never heard of that being done on Ducati singles, which evidently work well with zero at room temperature.
Positive clearance at room temp could cause too much play when running, which may be harmful to the bevel gears at the crankshaft, and cause timing variation.

From what else I've managed to glean from other posts, I'm aiming for zero play in the crankshaft, whilst still allowing the crank to spin freely without any hint of binding, is this correct?

[Samurai]

Thanks for the explanation Jordan, that makes sense and gives me a bit of confidence. I'll aim as close to zero as I can get, but am inclined to err on the side of a very small amount of positive clearance if I can't get it exactly bang on.

I'm a bit cautious after it was found that Ducati had over-shimmed the crank on my old ST4 (out of the factory!), by 0.2mm. This subsequently knackered the main bearings in under 10k miles and as it was long out of warantee it cost me a fair bit of time, money and the help of trusted Ducati independent specialist Louigi Moto, to put right!

[double diamond]

You do not need to have the transmission installed to shim the crank. You can use a bore gauge or gauge blocks between the two main bearing inner races of the assembled cases to get a close approximation of that dimension, then subtract the width of the crankshaft (measured as close to the pinions as possible but avoiding the radius, there is a slight step where the flywheel joins the pinion). The difference is the thickness of the shim you need if you're shimming to 0.00 mm. Matt

[Samurai]

Hi Matt,

Great advice and much appreciated. I've now installed the crank (without the transmisson) and torqued up the crankcase bolts so that the gasket gets fully compressed.

I'll leave it overnight but first impressions with the old shim installed are that I'll need to reduce the thickness. The crank can be turned by hand (just), but won't spin freely.

I've had the crank rebuild and services and installed new main bearings, which probably accounts for this.

Unfortunately I don't have a bore guage, but I do have a dual guage. I guess I'll just have to take a punt at a reduced shim size, reassemble and see if I can measure closer to a zero loading.

[Jordan]

If you organise for the crankshaft to have play, then that can be measured with your dial gauge to indicate what thickness of shims you need to add.
A convenient way to mount your dial gauge is to use a steel plate, drilled then screwed somewhere on one side of the engine. That can be a firm platform to mount a magnetic dial gauge stand.
The crankshaft can be pushed from one side to the other, maybe helped by lightly tapping with a heavy soft faced hammer.

[Samurai]

Hi Jordan,

I'd come to the same conclusion, but the tip regarding the steel plate screwed to the side of the enginecase is a good one, thanks bud

[Samurai]

Ok, I've followed the advice you guys have kindly given and have now adjusted the crank shimming so that when it's all bolted down correctly, I'm only getting 0.01mm play, read with a dial guage. I'm reading this when I carefully, but firmly, try and leaver the crank web side to side with a large screwdriver down through the barrel mouth.

As a double-check, the crank now spins a full revolution when using firm, fingers only pressure on the conrod from just after TDC. Does this sound about right?

[Jordan]

A 4 thou shim would remove that play.
I guess you don't have one?
As an alternative, if you had a hardened steel washer that is thicker than needed to take up all the play, that could be ground to the exact size required, using a surface grinder. That is common in metal machining shops.

[ducwiz]

From my experience, I recommend not to use shims thinner than 0.1 mm between crankshaft an main bearing, as they get sometimes ripped into pieces due to lateral movement of the crankshaft (caused by skew primary gears). I experienced this problem twice (on wide case engines).

0.01mm end play is OK for me, which is roughly the free play of the C3 ball bearings.

cheers Hans