Motorcycle Repair: Honda CB77, sheet metal frames, worst case scenarios

Question
Hi Bill, I've just finished a top end rebuild on my CB77 (rebore/new pistons/rings/timing chain etc) No problems whilst riding but there is a fair amount of what sounds like gearbox whine on the over-run (ie when the throttle is closed coming up to traffic lights etc using the engine as a break. Just wondered if this is normal?

Answer
Paul, after about 15,000 miles or so, there are some parts in the transmission which are usually worn significantly, even when maintenance is done regularly.

The low gear bushing has a central ring machined to keep it centered inside the two adjacent gears. Often the ring has worn off and allows the bushing to move around and/or the gears to move and also to tip in relationship to the meshing gears. The kickstarter pawls are always ratcheting inside the low gear and eventually will wear on the edge and cause the kickstart function to slip when using the kickstarter. When the low gear tips out of alignment, the kickstarter pawl's relationship to the inner face of the low gear is also compromised.

There are small roller bearings that ride on the kickstarter shaft and support the gearset on one end. If the oil hasn't been changed regularly, then the rollers start eating into the k/s shaft, causing noise and in worst case scenarios begin to rotate the k/s shaft when the throttle is turned on/off. You will see movement/motion in the k/s arm while driving.

Lastly, the primary chains loosen up, causing some noises due to slapping up inside the clutch cover as they stretch out. There is a primary tensioner roller which was originally a soft rubber, but hardens over time and becomes a hard plastic surface, which can generate some noise, too. There was a Honda bulletin aimed at Dream owners, which mentions that a certain amount of gear whine is not unexpected due to some resonance engine noises amplified in the sheet metal frames of the C/CA77 type chassis.

If there is bearing wear or gear teeth wear in the transmission, you will have additional noises under load/coasting.

I offer a full restoration guide CD with engine repair tips and lots more CB-related data covering all these issues and more.

Bill Silver
www.vintagehonda.com