Motorcycle Repair: Honda CL90, helicoil kit, valve seals

Question
Hi Bill, I am refurbing a 67 or 68 Cl90 for a friend. So far what has been done is the following: 1st over bore, NOS piston, new valves(seats were not cut, I lapped them in and tested for leaks, OK),valve springs, new gaskets and seals, new camshaft sprocket, valve seals. I checked the end gaps on the rings...one seemed slightly too large. I adjusted the valves and set the timing with a strobe. There was an intake leak that I fixed by using a helicoil kit for one of the manifold bolts threads, now it seems to seal correctly.

Now for the problems: first off the compression only reads 110 psi when tested cold with throttle wide open. The bike bogs a bit at high range and struggles to reach 45mph. And finally I hear what seems to be alot of rattling from the cam chain itself.

Thanks for any suggestions!
-joe

Answer
Joe, I think your cam timing is off one tooth. Compression should be 157-180 psi. You didn't say how much end gap you had on the rings. Does it have excessive blow-by coming from the breather tube? What does the spark plug look like? Does it smoke excessively? You DO have to break in the piston and rings for about the first 500 miles.

Late cam timing results in low compression and sluggish acceleration. It should wind up to about 58-60 mph, depending on the gearing combination you are using.

Probably should have replaced the camchain when you did the motor. The tensioner may be stretched out all the way, or the plunger sticking. If the ignition timing flutters and jumps back and forth with a dynamic timing light hooked up, then you have camchain slack, which adds to the late timing issues.

Bill Silver