ET: Engine (Twin) Tips to Replace Gearbox Seal

Rob H

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Think the gearbox seal has gone on primary side as the gearbox oil level is going down and the primary oil level is going up. I have reset the levels and will monitor with milage to try and find out the rate of leakage.

Anyone have any tips for removing the seal and replacing with new?

I vaguely remember replacing the drive side when replacing the drive sprocket and it being a pain, Think I eventually drilled it and screwed in some self tappers to pull it out
 

greg brillus

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The oil can also bleed out through the gearbox cover plate screws and even the lower locating dowel if it is not a tight fit, or if the cover screws have no sealant on them. The oil level in the gearbox is not really high enough to leak apart from a weep at most when the engine is running. Be interesting to see what you find.
 

BigEd

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Think the gearbox seal has gone on primary side as the gearbox oil level is going down and the primary oil level is going up. I have reset the levels and will monitor with milage to try and find out the rate of leakage.

Anyone have any tips for removing the seal and replacing with new?

I vaguely remember replacing the drive side when replacing the drive sprocket and it being a pain, Think I eventually drilled it and screwed in some self tappers to pull it out
I agree with what Greg has said above. How much is the primary level going up? It is sometimes/often the case that the primary level rises due to oil coming from the crankcase through the drive side main bearings.
 

Rob H

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Does the primary oil smell like gear oil?

Not sure what that smell like, but the gear box oil is going down and also I used Red ATF in the primary side and this has changed colour to a dirty brown/green ish.

Never thought about engine oil but oil consumption is low on the bike.

On the gear box I made a wood dowel dip stick and marked the levels on this to match the original bike dipstick. This allows easy identification of the level and also how much lower it is also. It was about 1.5 - 2.0 cms low. The primary side was up over the bottom run of the chain. I don't think it would be through the plate as this looked pretty well sealed and has not been disturbed since the rebuild by Bob Dunn, not sure about the dowl though.
 
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clevtrev

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Could also be a situation where crankcase pressure is bleeding through the wall `twixt crank and gearbox. That would blow out somewhere, do you have any oil coming out the kickstart cover end ?
 

Marcus Bowden

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Is it a Black Shadow ? as a member here in the SW Section and he always had problems with G /Box oil going down but to engine side, porous bulk head, he got rid of it and got a nice clean rapide.
bananaman.
 

Rob H

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Answer to both is yes, it is a shadow and yes looses a little from the kickstart cover but thought this was lost along the shaft?

Motor runs an elephant trunk breather so don't see how much pressure can build up to push thought the wall and displace oil in the gearbox which is also vented via the dipstick and holes in the cap unless I am missing something?
 

Len Matthews

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Is it a Black Shadow ? as a member here in the SW Section and he always had problems with G /Box oil going down but to engine side, porous bulk head, he got rid of it and got a nice clean rapide.
bananaman.
My gearbox looses some oil from the seal behind the final drive sprocket but I can live with this because the chain is always lubricated.
 

greg brillus

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Sounds like you will need to investigate to find an answer. The full oil level in the gearbox only comes up to the level of the two cover screws next up from the bottom two, not near as high as the mainshafts, these only weep a bit after a run. There are several possibilities I can think of, but they all require investigation. If you strip the primary parts away, clean down the gearbox cover plate and its surrounds fully, perhaps fill the gearbox to the full mark and leave it for some time and it may show itself. I use cans of either brake clean or contact cleaner and this cleans the area quickly and leaves the area dry. This should help find the leak, and this is important so you know what caused it in the first place, rather than strip everything in a mad hurry and not know what the fault was. Cheers and good luck...............Greg.
 
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