Sprocket tag washer - A Series Burman gearbox

Stanley Chappell

Well Known and Active Forum User
VOC Member
Is there a tag whasher on the final drive sprocket on a series a burman gear box.if you look at the burman parts list the tag whasher 17-1ba
Is omitted also various section drawings does not show it .i have 3 original gearboxes none have said whasher but centre punched to lock
The nut.The reason for my question if I follow good practice and use the tag whasher it binds on the back of the inner chain case .
The alternative spares list clearly shows 17-1ba tab whasher help appreciated.
 

A_HRD

Well Known and Active Forum User
VOC Member
Stan,
I'm still trying to fathom why your sprocket (or the tab-washer) is scraping against the back of your inner chaincase. Is the gearbox too far to the left for some reason? Fit up the clutch and check the chainline between that and the engine sprocket using a straight edge. Check the same from gearbox sprocket to rear wheel sprocket too. That might give us a clue?
Peter B
 

John Reynolds

Well Known and Active Forum User
VOC Member
With the standard Comet Inner Primary Chaincase (T4(2)) there is very little clearance between the spigot that protrudes from the back of the chaincase where the gearbox mainshaft passes through and the nut which secures the gearbox sprocket on the output gear of the Burman gearbox. The spigot on my original T4(2) has slight signs of wear from contact with the sprocket nut at some time in the past. However, it is important that the sprocket nut is held tight and this is the function of PR50-17-1BA. Omitting this lockwasher will liberate a little more clearance but the nut will have to be secured by another method and it would appear that centre punching has been resorted to in the past on a number of Comet gearboxes. Alternatively, one could reduce the height of the spigot.

Interestingly, the special inner chaincase which is supplied with the Alton Comet Electric Starter kit does not have a spigot at the rear of the hole where the gearbox mainshaft passes through but is completely flat. Whether this will lead to loss of lubricant or contamination with road grit entering remains to be seen. However, it does away with the clearance problems and one can fit the sprocket lockwasher without any concerns!

Peter brings up the interesting subject of chainlines. I'm sure that like many others I have just re-assembled standard bikes by the book on the assumption that the two Phils would have ensured at the design stage that the sprockets line up. However, when fitting the Alton kit it is necessary to shim out the new engine sprocket to line up with the clutch sprocket (and also shim out the sprag clutch to line up with the starter motor sprocket). This task is more difficult than one would imagine as it is not possible to put a straight edge on the sprockets but, having checked the primary drive, I thought that I would check the alignment of the final drive. This too is complicated by the fact that the rear subframe is not symmetrical and that the pivot bearing is offset to the rhs of the bike.

My calculations indicated that the gearbox sprocket and the rear wheel sprocket were more than 5mm out of line. Examination of the old sprockets confirmed this as the in-board side of the teeth of the gearbox sprocket and the out-board side of the rear wheel sprocket showed signs of wear. It maybe that my RFM is bent but the rear dropouts are perfectly aligned so I don't think so.

I believe that this chainline error occurred because the Comet was built around existing Series B Rapide components and a bought in gearbox and a compromise was needed. I have been able to correct 3mm of the error by putting a spacer under the gearbox sprocket (the maximum possible at that location). Full correction would require moving the rear wheel sprocket 2mm inwards - not an easy task while retaining the standard sprocket on brake drum flange set-up - so I think the chain will have to put up with the remaining slight misalignment!

John
 

Martyn Goodwin

Well Known and Active Forum User
Non-VOC Member
When working on the primary drive on my comet I use a sturdy straight edge ( a length of aluminium square rod approx 2" x 1") and hold it against the outer face of the primary case inner then measure the distance from the face of the straight edge to the face of the engine sprocket E215 and the face of the chainwheel on the clutch basket PR50-7X-1X. I have only ever needed to adjust the clutch basket by fitting suitable spacers in order to get the two sprockets to line up. As there 'should' be no movement between the clutch basket and the gearbox shaft you do not need hardened shims, and suitable washers will suffice.

The nut retaining the drive sprocket needs to be dead tight. Hint - you can obtain a Land Rover Hub Nut box spanner, 52mm which is a perfect fit for the nut , dirt cheap on ebay (example https://www.ebay.co.uk/itm/Hub-Nut-...520632?hash=item5b6c7350f8:g:NZUAAOSwmXteMVnw )

The locking tab washer is also essential. I also use blue loctite on the thread of the nut. Why?

Well I have twice had the drive sprocket nut work slightly loose in use (it gets a lot of back and forth loading on it when in use) and once loosened it allows the drive sprocket to 'worry' on the output shaft, eventually destroying the dogs on the drive sprocket, you would swear that they had been machined away - its a blessing that the burman drive shaft is much harder than the drive sprocket, given you need a Kings ransom to replace the drive shaft, but not so the sprocket.

I have never tried to measure the alignment of the drive sprocket to the rear wheel. I use a laser on the rear chainwheel to ensure it runs straight to the drive sprocket on the gearbox. Now that could be a COVID project!
 

nkt267

Well Known and Active Forum User
VOC Member
Just a thought..Does your gearbox sprocket have a machined recess on the side where the nut fits..It should if it is for a Vincent Comet. Panther and other mahes use a sprocket that is the same thickness al the way across..apologies if i've missed something along the way...John
 

delboy

Well Known and Active Forum User
VOC Member
Just a thought..Does your gearbox sprocket have a machined recess on the side where the nut fits..It should if it is for a Vincent Comet. Panther and other mahes use a sprocket that is the same thickness al the way across..apologies if i've missed something along the way...John
Gentlemen, we are talking SERIES A here.
Ta.
 

John Reynolds

Well Known and Active Forum User
VOC Member
Martyn,

The problem with correcting misalignment by targeting the rear sprocket on the front by means of a laser is that, while alignment can apparently be achieved by twisting the wheel in the dropouts, the result is that the axes of the two sprocket are no longer parallel and the front and rear wheels are out of alignment.
 

Marcus Bowden

VOC Hon. Overseas Representative
VOC Member
All my sprocket nuts & Burman G/B's main shaft kickstart side are drilled & tapped to take 2 BA grub screws that pass into the sprocket & lock titted.
 

John Reynolds

Well Known and Active Forum User
VOC Member
Oops, I hadn't spotted that it was a Series A Burman box. Is it on a single or a twin? The twin has a longer gearbox mainshaft so clearance is not be a problem in my experience. I have not worked on a pre-war single but you could try fitting a post-war sprocket which, as stated in post #6, has a recess machined out where the nut and lockwasher fits. The post-war singles had an 18 tooth sprocket as standard but VOCSC does list a 19 tooth one (PR50-22-19) which may have the machined recess that will solve your problem
 
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