Transmission noise

AZscrmblr · Post by **AZscrmblr** » Sun Sep 17, 2017 2:16 pm

A few months ago, a close friend of mine passed away and I was given a project bike that he was working on. It is a 1964 CL72 (CL72-1106221) with a CB77 engine (CB77E-1015295). It was a pretty complete bike when I got it and I have been working on and off to finish it. I now have it running and on the road. It runs well and is a joy to ride, but there is a whining noise coming from the transmission when you let off the gas and decelerate while still in any gear. The noise is not present when in neutral, accelerating or running at a constant speed. It also goes away when you decelerate and disengage the clutch. I am assuming that this is not normal. Am I correct?
I have done some research and suspect it may be a worn kickstarter shaft or bushings or possibly mainshaft bearings. Coincidently, I have some paperwork that came with the bike that shows that not too long ago, the engine was removed, the cases split and some kickstarter parts replaced. It does not say what the initial problem was or what parts were replaced, only that they came from a second motor that my friend supplied. I suspect that worn parts were used or not replaced.
I am considering pulling the engine and splitting the cases. If I do this, what should I be looking for and what parts should I be looking to replace?

mike in idaho · Post by **mike in idaho** » Sun Sep 17, 2017 4:33 pm

The 250/305 motors are 1950s technology and they do make a little noise, compared to more modern machines. There are three roller chains in there(four in the CB77), the cam chain the oil filter chain and the primary chain. The oil filter drive chain doesn't have a tensioner. The primary chain has a spring-loaded tensioner that allows the top run of the chain to go slack, on the over-run, some of that noise you hear is from those chains. Not a big deal, just the sound of old honest machinery at work.

AZscrmblr · Post by **AZscrmblr** » Mon Sep 18, 2017 11:29 am

Mike
Thanks for the response and the info. I can see where some of the noise is coming from the chains. However, it seems excessive to me. I am thinking that it is transmission related because it goes away when the clutch is disengaged. I don't think the cam and oil filter chains are effected by clutch engagement/disengagement. I suppose it could be the primary drive chain.