Monza high compression...

[el_guru]

Thanks guys for all the advice on the rattly head which I have managed to resolve.

So now my issue is that it ran ok but has VERY high compression. I can stand on the kickstart and it doesn't budge with the compression. There,s no compression release unlike my 350 and own a race Velocette KTT as well as Norton singles so no stranger to high compression.

I checked the compression and it comes up to 170 psi...!!!! I don't have any vehicles that get that high so any ideas would be welcome.?

Thanks.

[Jordan]

In the parts books, there are various types and thicknesses of cylinder base gasket available for singles.
I've seen aluminium and paper ones. You could try stacking some of these under your cylinder to affect a lowering of CR.
One of the advantages of bevel drive is that you don't have to worry about variation in head height affecting the camshaft drive, as the semi-circular shaft coupling copes with it.

How did you fix your rattly head?

[Nick]

The older British singles, being long-stroke under-square engines, are probably not an apt comparison. The Duc not only has a relatively shorter stroke, the kick starter doesn't have all that much leverage. Thus, the compression may seem much higher than it is. In starting my 250 Diana I always put it in gear, roll it backwards to bring the piston to compression (which works out to just after TDC on compression when going forwards) and then kick, or push start. My 350 has a release which I always use. Never just kick it without knowing where the piston is.

Still, it might not be a bad idea to confirm that you've got adequate squish clearance and valve/piston clearance.

The alu base gasket/spacer from the 350 will raise the whole plot upwards about a mil.

[el_guru]

Thanks Guys....

Jordan I fixed the rattle by finding the upper bevel drive bearing carrier was spinning in the head due to previous owner installing 2 thick gaskets which didn't support the bearing carrier and allowed it to move. Loctite bearing goop and proper gasket solved it. There were other clever remedies on the thread.

Nick, I haven't just bashed away at what is a fragile component but tried to ease it through to beyond TDC. I shall try backing it whilst in gear but I,m still amazed at the 170psi I am getting...!! I guess I need to take it all apart again and put a thicker base gasket on fortunately I do have one.