Help please with gearbox whine

bob southall

Forum User
VOC Member
I have just completed a full rebuild on twin. Everything works but on take off I have a loud whine coming from the gearbox. The noise start immediately as the clutch is engaged but clears once the engine reaches about 2500 rpm. On changing up the noise returns in all gears until the engine reaches the higher revs. It sounds like a really badly meshing pair of gears. The noise is only produced with power on and disappears on balanced throttle or overrun. It is engine speed dependant

Has anyone experienced this or have any ideas of the likely source?

I have checked the oil in the box and the primary case and both remain clean with no debris.

The rebuild included refurbished crankcases and crank, new clutch linings, Alton alternator, Grossett electric start etc etc.

Thanks in anticipation of any help

Bob Southall
 

Marcus Bowden

VOC Hon. Overseas Representative
VOC Member
Bob my handsome try removing Alton drive sprocket, you have not mentioned any replacement of gears. "If" it goes then it is likely to be worn chain on worn clutch sprocket. It happened to me after a rebuild and fitted a cut down Bosch dynamo secured directly to the back of the drive housing with three screws behind the sprocket. Under power the chain rides up over the worn sprocket and binds hard up against the Alton sprocket.
bananaman
 

bob southall

Forum User
VOC Member
Thanks for all the input.
I Checked the alternator drive and there appears to be plenty backlash although there is not enough access through the small window to measure the vertical clearance.
I removed the alternator drive wheel and found the noise was no longer present on test. The alternator is sealed in place with silicone so I was able to lever the unit up a little and slip two 4 thou shims in the cradle. It now runs quietly but I regard this as only a temporary fix.
It is a new engine sprocket (to suit the added oil seal) and chain but I judged the clutch sprocket to be OK. There appeared no hooking or one sided wear on the teeth as normally associated with a worn sprocket. I set the alternator wheel up with about 15 thou clearance.

I suspect I will have to pull the chaincase off and check the clearance to see if I made a mistake and if not fit a new clutch sprocket.

Once again thanks for everyone's help.
Bob Southall
 

TouringGodet

Well Known and Active Forum User
VOC Member
VOC Forum Administrator
VOC Forum Moderator
When I recently fitted an Alton to the Shadow I had noise, and for me it was the side to side clearance, I pushed the Alton in farther towards the clutch a smidge and all is quiet.
 

Len Matthews

Well Known and Active Forum User
VOC Member
Thanks for all the input.
I Checked the alternator drive and there appears to be plenty backlash although there is not enough access through the small window to measure the vertical clearance.
I removed the alternator drive wheel and found the noise was no longer present on test. The alternator is sealed in place with silicone so I was able to lever the unit up a little and slip two 4 thou shims in the cradle. It now runs quietly but I regard this as only a temporary fix.
It is a new engine sprocket (to suit the added oil seal) and chain but I judged the clutch sprocket to be OK. There appeared no hooking or one sided wear on the teeth as normally associated with a worn sprocket. I set the alternator wheel up with about 15 thou clearance.

I suspect I will have to pull the chaincase off and check the clearance to see if I made a mistake and if not fit a new clutch sprocket.

Once again thanks for everyone's help.
Bob Southall
Bob, you mention that the Alton is sealed with silicone. This issue has been raised before. By sealing the alternator/dynamo you prevent the primary chaincase from breathing which it needs to do- right Hugo?
 

Don McInnes

Well Known and Active Forum User
VOC Member
I monitor levels routinely & top up as required, no problem with whine
 

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Hugo Myatt

Well Known and Active Forum User
VOC Member
Bob, you mention that the Alton is sealed with silicone. This issue has been raised before. By sealing the alternator/dynamo you prevent the primary chaincase from breathing which it needs to do- right Hugo?

Absolutely right, Len. See 'Another Ten Years' for the saga.

Hugo
 
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