Quote Originally Posted by zhu View Post
i think what you are looking at there is the decompressor which holds open one of the valves when the engine is spinning on the starter.
it should then allow the valve to operate normally once the engine fires

and yes it will make a hell of a racket if it gets out of line
thanks, zhu.

I'm looking at the exploded diagram of the JH600 upper head, with the camshaft and valve assemblies, and can see this part clearly. Alas, I cannot make out in the diagram how it is activated and how it links to the intake/exhaust valves. I've googled a bit for "decompressor single-cylinder four-stroke motorcycle engine" and the like, but not found anything truly instructive.

So what you and Lao Jia Huo seem to be saying is this mechanism intervenes in the normal exhaust/intake valve operations during and only during startup to achieve some desired effect, such as, err, starting up the engine? Or starting it up more efficiently/smoothly than in the absence of this mechanism?

EDIT: Hmmm, I do have contacts for a guy here in Shanghai who's with the liaison office of AVL GmbH, which provided the design and engineering for our JH600 engines. I'll try again to track him down.

Motokai and I did get a glimpse recently of the phone-book sized JH600 shop manual, all in Chinese of course, and damn I'd like to lay my hands on one of those. The guy who is working on Motokai's engine does NOT have one of these shop manuals. There's probably only one in all of Shanghai.

Wonder if Jialing would sell me one, as they did with the service parts catalog?

cheers