The BSA A7-A10 Forum
Technical (Descriptive Topic Titles - Stay on Topic) => A7 & A10 Engine => Topic started by: jelo68 on 09.07. 2026 22:44
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Hello ,
a Friend from Munic is on a Visit whit his A7 Bobber cause he has Problems with his Caburetor. This is fixed - the old 276er is dead. We mounted a 626er and the Baby is a onekickwonder. Also he has Problems whit his E3l - Parts to fix it are ordert but i can move the Drivegear on the crank 4-5mm in axial way.
I dont know what is the Problem?
Any Answers?
Cheers Jens
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This post is headed "dynamo drive" but the drive gear on the crank has side to side movement. That is how I understand it......something different.
The drive gear on the crankshaft is locked in place by the oilpump drive gear and lock nut. These have a left hand thread. So if there is movement here it must be the crank itself moving, and this is the familiar problem we call Crankshaft End Float. Plenty on the Forum about causes and how to fix.
So the problem described could actually be too much in/out movement on the dynamo drive gear, not the crank.
The dynamo drive gear fits on the idler gear spindle with a plain taper. There is a cork washer underneath this gear which controls the movement "end float" on the spindle. My guess is that this cork washer is missing. Naturally the idler gear has to be pressed into the right place on the shaft, as this affects the dynamo chain chain alignment. When assembled the cork compresses against the inner timing cover and the dynamo gear should end up with no end float. Simple and crude, but does the job. Dynamo chain runs in grease, it has no oil supply. Without the cork washer oil can work into the dynamo chain cavity via the spindle bush bearing in the inner timing cover.
Swarfy.
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Yes the korkseal is missing Thanks...GrußJens
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Time to find some cork and make something that will do the job. Reckon a wine bottle cork is too small, but open one just to check.....,,.
Swarfy.
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Hello Jens,
67-0708 idler pinion oil seal is not a cork washer, its a thin felt washer behind the sprocket.
https://draganfly.co.uk/product-category/bsa/sparesparts-for-bsa-a710-b3133-c101112-m202133/engine-gaskets-gearbox/timing-gear/pre-unit-a-group-gear/
The idler pinion should have no sideplay when sandwich plate fited with gasket.
Normaly when its fited without gasket it is locked or its hart to turn.
I guess the faceside from 67-286 is worn or bush replaced without face.
So tell your mate to have a close investigation, because when he fit a thick washer behind the sprocket to elimate the sideplay, the chain is not in line with the dynamo.
Never have seen such sideplay on all my engines.
regards Klaus
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well unless over many years felt has been put behind the idler pinion i have messed up loads of engine builds and re builds , as far as know from the year dot it is cork, bar is now open *beer* *wave*
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Yes, Klaus has made an important point. There will always be a runnining clearance on the idler pinion dependant on the thickness of the faces of the idler spindle bushes.... two different part numbers here, although the bushes are the same size, the internal oil scrolls are cut to oppose each other and feed oil towards the idler gear. Get this wrong and the dynamo cavity gets filled with engine oil. The washer (cork in Drags example) serves to locate the dynamo drive and eliminate end float on the idler spindle by keeping the idler gear lightly pressed against the face of the outer bush.
Swarfy.
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May be BSA replased this corkwasher to a felt one in the late 50th till end of production.
I know only the felt washers.
But Jens talk about 4-5 mm sideplay, I would tolerate 1 mm but not more.
regards Klaus
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Hi All,
On a similar non issue,
I have a belt drive to the dynamo, its been on there 20 + years without issue.
Recently the bike stopped charging, it had been intermittent recently so i first thought the belt was failing.
Last time I had the timing cover off was when fitting an ATD during the elect start conversion.
I'm pretty sure I put grease in the belt compartment, as recommended by SRM.
Cover off revealed that the belt is fine but the grease had dissapeared *????*.
Further tests which I should have done first reveal a failed armature *sad2*
A new one is on the way
John
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That outer bush scroll pushes lubricant towards the idler gear, so this pesky washer is actually stopping grease leaving the cavity, rather than oil coming in. Reckon CJ's grease has found an escape route and happily dissolved into the engine oil. We all make the assumption the P. O. assembled without grease when the cavity is dry, so a time to time check is in order as the washer has a big ask.
Swarfy..