Motorcycle Repair: CL350 engine rebuild question, honda cl350, head gasket

Question
QUESTION: Hello,
   I am rebuilding a 1972 Honda CL350 and I have run into a problem. I can't turn the engine over for the right half. It turns over fine on the left. It would turn over, albeit with some resistance, when I didn't have the top cover on. The engine would pop up when the right side valves were going. I believe I had the cam timing right. Do you think it could be the valves hitting the pistons? I looked in the spark plug hole and the valves seem far away from the pistons but I am not sure I know what I am looking for. This is my first time rebuilding an engine so maybe its a simple thing that I overlooked.---Marc

ANSWER: Marc, what parts did you change and install?  

There is a service bulletin for 350s that covers the changes in the camshaft lobe height and that they can run into the cam cover webbing for the inside lobes. If you are reusing the parts that came out, then probably you have the cam timing set incorrectly.

Cam sprockets for the 350s have a flat side portion of the sprocket that needs to be horizontal with the head surface when the left side piston is at TDC.

Bill Silver

BTW.. the camsprocket bolts are NOT interchangeable. The one with the shoulder goes on the bottom. Threaded one goes to the top, next to the flat side of the sprocket.

---------- FOLLOW-UP ----------

QUESTION: Hello, thank you for the response. I put in different pistons and another valve head. The parts I am using are used. I thought I had the cam timing correctly and I checked to see after the side covers were in whether the timing mark (the L with the line through it, right?) was still horizontal at the top of the sprocket at LT mark on the rotor. The only thing I can think is that I don't have the cam timing correct but there don't seem to be any other marks on the sprocket. There's two X's in circles and also some bumps on the other side of the sprocket.

Answer
What pistons did you use? Overbore/big bore? Did you use an OEM head gasket?

There are two marks on the rotor.... LT (top dead center left side) and LF which is the timing mark for the ignition timing. The L mark on the flat of the sprocket should be at the top, the flat part level with the head surface.

Again, if you intermixed early and late cam housings, there is a slight chance that the cam lobes are hitting the inside front of the housing. Probably the only way you can check it, is to take the camchain off and then reinstall the end bearings, then try to rotate the camshaft in the carrier. If it turns through without hitting anything, then the remaining issues would be oversized pistons hitting the inside edge of the fire ring on the head gasket and/or pistons with too much deck height so that they are hitting the head. Assuming that the head has no bent valves, then incorrect cam timing would be the other reason for pistons hitting the valves.

You don't have the sprocket on backwards, do you? I'm not sure that you can do that with this type of sprocket, but I don't have any engine parts here to remind me. The recess in the damper material on the sprocket fits over the camshaft flange.


___  cam sprocket
 o

LT

Bill Silver