Motorcycle Repair: Cylinder compression, dnepr bike, piston crown

Question
Hi

This is a question that is based on a Russian Dnepr bike, but it's a 'general' question, such as it is :)

I just replaced the cylinder gaskets and put everything back together (the old card gasket was in bits and there was an oil leak).

When I tried to start the bike it felt like the compression or stiffness of the kickstart has increased dramatically - and was almost impossible to move at certain parts of teh rotation.

Do you think I may have screwed the head on too tightly? Do I need to adjust the tappets?

Any ideas?

Thanks in advance!

All the best

Trevor

Answer
Trevor
Even though I don't know much about your bike, your question itself told me a lot about what you did and where the problems may lie.

When you reassemble the top of any engine, the tappet clearances will change. This is because the thickness of the new gasket may not be the same as the old. If you did not loosen then before final assembly, you have run the risk that a valve is now comming in contact with with a piston crown. (exhaust stroke, valve open, piston at top dead center) So, yes, they need to be checked and adjusted.

The second danger point is bolting on the head. If you did not tighten the head bolts in proper sequence, a little at a time, to the proper torque specifications, then there are a couple of things that could go wrong. The first is that the bolts may be too tight in one spot and not tight enough in another. This could warp the head. The second is that of not tight enough, compression could blow by the gasket with fire eventually eroding the gasket, or mating surfaces.

It is my opinion, that if you did not follow proper procedures, that you do some research, find a service manual if possible, and re-work the job, using new gaskets. The old ones may be crushed.

John