Gearbox/Clutch Noise w/video

[Brian G]

Good Day All -

I'm hoping one of you can help diagnose the cause of what I believe to be a clutch or transmission whine emanating from my newly rebuilt CB400F. It can be heard only when power is being transmitted to the rear wheel - i.e., there is no noise in neutral, or in gear with the clutch disengaged but if I place the front wheel against a wall and feed in the clutch a little, the whine becomes apparent. When getting underway and accelerating, it is quite pronounced but at steady roadspeed, it reduces somewhat. On trailing throttle, I can't hear it at all. Clutch operation is smooth, with no dragging or slipping, she snicks up and down through the gears nicely and neutral is easy to find.  Search results from the two forums suggest it may be normal or it may indicate imminent catastrophic failure! Hopefully the video will help narrow it down.

https://youtu.be/2tdTc9uSn_U

Full disclosure, here: after reassembling the clutch, there was a part left over I wasn't too worried at the time, as I couldn't see anything resembling it in the parts manual exploded view and it wouldn't have been the first time a part from the CB450S my step-son was rebuilding in the same shed found its way into the my 400F's parts bins. I'm thinking now it might be relevant. Can anyone identify the part?

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Hopefully, the noise is coming from the clutch, as otherwise I'm afraid I'll have to split the cases again and I really don't know what I'd be looking for as all the bearings were replaced during the rebuild!

Thanks and Regards,
Brian

[mike the bike]

I don't recognise that part and I've not long reassembled a 400 clutch.  What diameter is it?

[Clem2112]

Sounds like a few 400 fours I have heard , from memory. Maybe a bit louder though.

Some have suggested that a new primary chain running on the original crankshaft and intermediate shaft will produce more 'whine' under load.

That part looks like it has a decorative/protective plating on it , so maybe an external item?....does not appear to be 400f though.

[Brian G]

It's 26.5mm O.D., the central hole is 9mm dia. and it's 4.5mm deep.
As they say on e-Bay, "Thanks for Looking"

Regards,

[Anders S]

Hi Brian G,
Did you find the root cause of this whining from clutch/gearbox?

[Athame57]

Could the cam chain be too tight?

[Anders S]

My 1975 sounds exactly as Brian’s. Noice is only when you put load on drivetrain/engage clutch. I guess if it should be cam chain the noice should be all the time, without load also.

[Athame57]

I guess if it should be cam chain the noice should be all the time, without load also.

Yet this is what happened to me, it sounds the same if more acute. I amended and it went away.

[Anders S]

Thank you! I released the tensioning screw and fastened it but no change.
Any other suggestions?

[smoothoperator]

I think it was BryanJ that mentioned putting some tension into the cam chain by pushing down on the kick start whilst making the adjustment. Maybe worth a try?

[Anders S]

Hi,
I found out the issue on my bike. It was the 23108-333-020 Secondary drive gear that was worn-out. Actually I do not see any pitting or any sign of worn on the gear but it is. Maybe you can measure it.
I changed gear to a new one on got rid of the sound like in the original post.

Kind Regards
Anders