Top end cam rattle

[Karlos]

Hi All
Just wanted to pick your brains a bit. I notice there is an earlier post regarding strange top end noise when the throttle is blipped and the revs settle down. My CBX top end noise is happening on the overrun, accelerate and slow down there is a distinct thrash noise which I'm pretty certain comes from the cam gear, once the revs drop below ~2000, all well and the gentle purr of the engine returns. Its almost akin to the tension shifting on the cam chain as the wheels drive the engine as you slow down, eventually the balance is restored to the tension system becomes "in charge" again . Any comments or advice as always appreciated.
PS does the CB900 cam chain tensioner fit the CBX, looks pretty similar ?
Many thanks
Karl

[daves79x]

Sounds like you are describing the 'chirping' noise the alternator clutch can make. It goes away at idle. The excessively noisy valve train many notice in higher-mile bikes can be remedied by installing oversize Oldham couplers, available several places. If your noise goes away immediately upon pulling the clutch in, then it's the alternator. If so, that needs addressed with a new spring, shims or new plates.

Dave

[robsgreen]

Hi Karl
I think it was my post you read. I have now stripped my engine down because of a vibration issue which is being addressed at the moment. I also wanted to look into the problem you describe as a thrash noise (good description). I too suspected the top end but can find absolutley nothing wrong with mine. I've carefully checked the bottom end and have also found nothing. I'm replacing the main primary shaft bearing as a precaution even though it feels fine and the clutch side bearing, again as a precaution. my is fine when warming up and after short rides but starts making this noise when its very hot but but vanishes as soon as the bike has cooled for a few minutes- very strange.
Martin

[daves79x]

Martin - have you looked into the oversize Oldham couplers? They WILL cut down on top end noise almost completely. My 45,000 mile '79 sounded like a noisy sewing machine before and is completely silent now.

Dave

[Karlos]

All
As always ideas and thoughts to follow up one, I'll keep you informed of my progress
Many thanks Karl

[robsgreen]

Hi Dave,
I checked my couplers and each end of each cam seems a good sliding fit with no detectable play. Maybe I should change them anyway to close that loose end. Im determined to sort it out. How tight would oversize ones be? my bike has done 14k.
Im picking up my crank this week with balanced con-rods so build will start soon.
Regards
martin

[daves79x]

You really can't detect play in any of them, no matter the miles. With only 14K though, they should be rather snug. You freeze the oversize ones before installing them.

Dave

[robsgreen]

Thanks for that Dave, Im going to have another look now.
Best Regards
martin