My 1956 Dominator 99 has a bad clatter from the engine. Very audible.
It is not a bearing rumble. nor a tappet rattle, nor a chain slap.
It seems to be coming from the front of the engine.
The engine has not been run much since rebuilt - probably 15 years ago. Probably not done 100 miles. Compression test shows 120 psi both cylinders (at 1000m alt)
I suspect a camshaft/cam follower problem.
Does anyone have any experience or suggestions on this before I strip it down?