SOHC.co.uk Forums > CB350/400

Gearbox problem

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sye:
Is the chain run straight? Check it with a plank or better still a laser tool. If it's off by more than a little, the chain catches on the front sprocket sides and you would only hear it when pushing the bike or moving slowly.

ka-ja:
Or maybe a problem with the primary chain?

florence:
I'm assuming from your original description that it doesn't do it in neutral?

flatfour:
My friend had a similar problem with his 1970 CB750. It came on quite suddenly and could only be heard when slowing almost to a stop, when it was loud enough to notice from another bike if you rode slowly alongside him. At this time he had owned the bike for some nine years and the total mileage was around 35,000. No work had been carried out prior to the problem developing.

The engine unit was dismantled and rebuilt, with no faults evident. After this though, the problem disappeared and did not re - emerge in the following 6,000, or so miles that passed under its wheels before it was sold!

In addition, a CB750 K6 that I owned and then sold to the same person mentioned above developed a rapid "tick" from the chain case area after a new "O" ring chain was fitted in place of the original. This however was easily solved, as the new chain was simply too wide and a replacement non - sealed chain immediately put matters right.

taysidedragon:

--- Quote from: florence on January 28, 2020, 09:36:28 AM ---I'm assuming from your original description that it doesn't do it in neutral?

--- End quote ---

I didn't click it into neutral while still moving so I don't know. Can't check it now because it's in pieces.
I've double checked the chain and sprockets, nothing touching or clicking, no sign of any contact anywhere. There seems to be a lot of in and out movement of the gear change shaft, a lot more than on a spare engine I have. 😯
If there was a worn primary chain then I would get the clunking in 2nd or 3rd gear when slowing down, wouldn't I?
Either way, it looks like engine out to investigate. 😣

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