Motorcycle Repair: honda cb450 1971, honda cb450, cams and followers

Question
Had low compression in bike that I bought. So I pulled the engine out and had cylinders honed head reworked. Put back together checking the marks on cams when replacing cam chain. When I turn it over I have very good compression in left cylinder but little in right? I put new rings in also. I check the valve timing several times and every thing looks correct. I pulled the head off to check for stuck valve but there is not one? Just weak compression in right cylinder?

Answer
Howard, you can determine the loss of compression with a leak-down tester, which is basically a controlled air source pumped into the cylinder at TDC compression. A gauge on the tester compares the source air supply readings with those that are being maintained in the cylinder. A certain percentage in the less than 5% is to be expected, but readings greater than that indicate a leak which can be determined by listening for air escaping the cylinder... intake valve, exhaust valve or piston rings (assuming no damage to the head gasket).

If the head was thoroughly rebuilt, close attention should be made to the condition of the cams and followers/lifters. Worn cam lobes will result in less air in, reducing the compression readings. Make sure that the valve adjusters are set up so the index marks on the ends of the adjustment shafts are pointed outwards from each other (/) (\). If you rotate the marks inwards, the cam follower will be on a different geometry angle, which will change the valve timing and thus the intake charge.

If you had good compression in one side, then the cam timing was probably correct. Sounds like a valve sealing issue or camshaft problem.

Bill Silver