Motorcycle Repair: 1972 honda cl100 scrambler, honda cl100, cam bearings

Question
Hi,,I found an old honda cl 100 and it had compression(seemed to).I put a new charged battery on it and the lights came on..i didnt seem to get spark.Then they kick starter woulnt go down, really stuck. I turned and rocked the crankshaft but it seems like something in the cylinder is binding,.could this be rings? bent rod or valve. honda single 4 stoke. thanks very much.what would cause it to bind internally, is it worth tearing down? I have average mechanical ability..but willing to try. thanks   JON

Answer
Jon, when these bikes sit for years, often the air inside the cylinder condenses moisture that collects on top of the piston and rusts the rings in the piston grooves and into the cylinder walls. Sometimes they will break free with some penetrating oils and turn over, but often the rings are stuck and that reduces the engine compression too much.

You may be feeling the piston/rings passing over the rust spot in the cylinder.

The other major problem is that the cams get loose in the cylinder head and that causes the ignition point gap to wander around excessively. Check the cam for sideplay in the cam bearings before you sink a lot of money into this bike. Cams can be fitted with needle bearings at a machine shop, but that gets costly.

At this point you don't have much to lose by pulling the motor out and tearing down the top end to see what kind of issues are inside.

www.cmsnl.com and www.bikebandit.com have on-line illustrations of the parts in exploded views. If you have a decent set of metric tools, an impact driver for the screws and a little patience, you can learn a lot from this little single.

Bill Silver