The BSA A7-A10 Forum
Technical (Descriptive Topic Titles - Stay on Topic) => A7 & A10 Engine => Topic started by: mark on 30.11. 2010 08:38
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just checking that I'm on the right track with this as neither motor that I disassembled had one fitted. Does this seal go in behind the dynamo drive sprocket? The only seal left in my gasket set is a cork washer about 3/16" thick which seems to be the right diameter and will squash like the breather seal when the sprocket is tightened.
Regards
Mark
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Yep,
that's the one.
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Hold it! There can be a variation in the gap the cork has to fit into. If you compress the cork too much, bear in mind you can't see what's happening there, the cork will split, disintegrate and end up spread around inside the case. I had that and ended up carefully trimming the thickness of a new cork seal down to a lower compression. A recent strip shows it's still doing its job unlike the first attempt. Work out the gap first and compress the cork on the bench by hand to see if you are happy with the fit first. Best to take the time to do this and add a little grease onto each side before fitting it.
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There can be a variation in the gap the cork has to fit into. If you compress the cork too much, bear in mind you can't see what's happening there, the cork will split, disintegrate and end up spread around inside the case
spot on Andy, I found my idler was not that tight on it's shaft so best pull the sprocket up tight first as the dynamo sprocket might pull the shaft through a bit.
SRM supply both cork and felt washers with there belt drive kit so it would seem felt is also usable and might be less fragile than cork.
last time I took my case off the cork had chewed up and was lying in the bottom of the compartment but no oil in there (belt drive) so probably if shaft and bush are good it's not a great issue
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G'day Mark,
It was after 20 years of riding the '51 that I found out about that seal, but in all that time very little oil found it's way in. Wish this place was around back then. Recently I fitted belts to both of mine. One from SRM and the other from Lytedrive in Melb'. The SRM kit fitted to the cafe ate the felt seal in a day but no oil was getting in. The Lytedrive kit in the '51 has a different ratio so the dynamo had to be adjusted (rotated) quite a bit to tension the belt. This meant the cork seal at the dynamo was not sealing properly. Oil now coming through the bush into the compartment. This leads me to think that if the dynamo is not sealed against the inner cover crankcase pressure will try to escape that way taking oil with it.
Just my thoughts, may be wrong.
Cheers
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Good one Muskrat! I agree with your thoughts. Sealed properly the pressure in the inner case can't force oil through the bush (just enough to lubricate) if the dynamo gasket fails this would allow pressure fluctuations to happen in the outer case and encourage oil to pass through the bush. P.S. Muskie did you pick up the barrels yet?
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I dispense with the cork washer, and machine the sprocket side of the boss, to take a CR7411 low profile lip seal.
Richard
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I do the same as Richard.
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Good one Brian; who says that croweaters aren't smart?!
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OK Richard ya got me, so a croweater is -------
Don' tell me it does what it says on the tin
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A croweater is similar to a sandgroper but lives in a different place.....................
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Croweaters might not be dumb but have no idea how to make beer.
Their local drop is akin to drinking horse p*ss strained through a dirty sock.
and Brian, before you send a hit squad up the road, its Southwark we're talking about.
cheers
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I consulted Wikipedea, found the answer but no explanation as to how they came about.
Anyway I should talk living between Jocks and Geordies and further down the coast Makems and sand dancers
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Call them (Sand grown uns) round here. :groan: