Motorcycle Repair: CL100 engine/trans noise, shaft bearings, clutch lever

Question
I have restored a 1971 Honda CL100. I did not do anything to the engine or transmission other than clean the carburetor and change oil. The bike only had 1400 miles on it. It starts and runs fine and the clutch/transmission also work fine. However, there is a significant whining noise that seems to be coming from the transmission. It does not appear to be in the engine because there is no noise when the engine is reved up in neutral. I put the bike on the centerstand and shifted it into gear, but there is no noise. I only hear it when I am riding the bike and it is under load. The noise is noticeable in all gears but more so in the lower ones. It goes away when I pull in on the clutch lever. I changed oil to Amsoil 10w-30 and it may have helped a little bit, but the noise is still there.
I know that these bikes were somewhat noisy. Should I be concerned about this noise?

Answer
Gary, I have to ask the obvious question first...  How tight is your drive chain? An over-tightened chain, under load with a rider will sing pretty good, plus it puts extra loading on the output shaft bearing.

With that out of the way, I would probably pull the clutch cover and take a look at the clutch input shaft bearings/clutch basket.  Looking at the microfiche drawings here:

http://www.cmsnl.com/honda-cl100-scrambler-100-k1-us_model530/partslist/E++11.ht...  I see a LOT of superseded part numbers, which either means that Honda felt that they needed improvements on the parts or they were just consolidating part number for all the applications.

With the clutch cover off and clutch removed, you can turn the transmission gears (disconnect the drive chain) and see if they feel rough and/or if there is signs of metal debris in the bottom of the clutch cover or near the oil pump pickup, indicating some kind of parts failures.

Unfortunately, if there are parts problems with the transmission, the whole engine must be dismantled to split the cases for gear access. Other than a rotor puller tool, not much else is needed in the way of special tools to tear the motor down.

Bill Silver