Rebuilt the gearbox with a refurb kit - all ok, but the "whirring" sound is still there - may be coming from the bottom end. The Big-end bearing is the only thing that is still original as didn't have any obvious problems - could that be making the noise?
The big end bearing will…
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noise
hello,
not the same bike or setup as yours. but i had a similar noise. which as i found out later was that a drive cog had been fitted to the dynamo that was not the correct one. it had the same amount of teeth but the dynamo drive cog teeth were sitting on the bottom land of the timing case drive cog, not meshing correctly. which shredded the fibre one.
like i say i didnt know it was the dynamo cog at fault at the time .so i replaced the fibre cog with a metal version in the timing case. and then on starting the bike, it sounded like one of those world war 2 wind up sirens. so as i found out fitting a new dynamo cog, cured it.
barry
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Tha's easy enough to check -
- the dynamo will come off by loosening the clamp and removing the acorn nut on the end stud.
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The big end bearing will make a knocking sound and worn main bearings will rumble so it's unlikely to be either of those. From the video you posted up it sounded like a gear mesh issue to me - so maybe in the timing case?