Motoscrubs.com

Hi,

This will save you some time looking-
Nigel helped me out with this-top guy.

Happy New Year everybody

Hello All

As has been said, only a few models were originally fitted with base shims, like the 250 Monza and 350 Sebring. Base shims are mainly used for race use to set an accurate squish clearance (piston to head clearance). Running a close clearance improves combustion and when the clearance is tight then shims are preferable as gaskets can compress in use, potentially to an amount where there could be contact. When the engine is at temperature and under load the clearance will close up, hence the reason to set a safe squish. Clearing when cold, doesn't guarantee clearance when running.

The issue with road bikes is that over the years parts get swapped, machined etc and it's sometimes not prudent to assume everything is "stock". Therefore a quick check is generally a good idea and base shims can be used to correct any issues (either with or without gaskets). Stacking up gaskets, unless the clearance is large is not ideal as they will compress in use.

For a road bike I like somewhere between 0.75mm to 1.5mm clearance depending on the build, with a min of 1.0mm for a 450 using a gasket.

For race use I run 0.6mm to 0.8mm on a 250/350 and 0.8mm to 1.0mm on a 450. For race use I only use base shims and a good quality setting sealant. Of course in moderation, with care and not with a trowel or from the tube!

Regards Nigel

Good clarity there, thanks Nigel. Do you know if Mototrans always used the alloy shims? Both my 250 and 350 Wide case Mototrans engines have them fitted.

Cheers,

Colin

LaceyDucati wrote:For race use I only use base shims and a good quality setting sealant.

What is your opinion on the copper spray as a sealant on the aluminum shims?

Aye Colin,

Have a good New Year to you All, if I may?

The late 350 MotoTrans engined Ducati widecase that I acquired 20 years ago, did not have any compression plate fitted between the barrel muff base and the crankcases.

Since having the off-centre bore rectified, I will be checking the piston clearance from the head on TDC and also the valve/piston clearances. The head is not the "original" item and I have a new piston and valves from Nigel, so plenty of potential variables to check!

Good health, Bill

Happy new year Bill, My 350 mk3 engine which is the same as yours has no cylinder base plate fitted from new.
Cheers, George

Slainte, George.

Bill