Drive side oil leak plunger A10

[BrummieJon]

Now I've got my 1953 BSA plunger A10 running I appear to have an oil leak coming from behind the drive side crankcase sprocket.. When I rebuilt the engine it had new mani bearings, shims and a new crankcase oil seal... Then the engine sat on a bench for 15years... I think the oil seal may have gone hard over time... Should I give it a bit of time to bed in or get straight down to splitting the crankcases again... Its taken so long because I've been ill for quite a while and circumstances halted my progress, now this, another setback..

[DAVE BRADY]

Hi Jon,

Good to see you back and your bike is running.
I would think that seals go hard though use rather than just age. Anyway, if decide to replace the seal you should only need to strip the primary drive.  With cushdrive spring and sprocket removed you can get at the seal.

Dave.

[BrummieJon]

It's been so long since I've been that deep I forgot how the seal is fitted. The leak is definately from there. A new seal is about £10 so I'll be stoked if it's that easy... Cheers... It's been a long time getting here but it's a passion project on a very ordinary BSA. An everyday family lugger..

[V500]

Now I've got my 1953 BSA plunger A10 running I appear to have an oil leak coming from behind the drive side crankcase sprocket..

Sucking eggs and all that, but I don't see how that would be a visible leak to the outside?
Sure it's not the engine breather pipe dripping...as they do?

[idie]

The early A10 didn't have an oil seal. Hence with a bit of wear they can leak.

[V500]

The early A's had a oil thrower rather than a seal, and I don't see how that could wear, though if it did it would allow engine oil into the primary chaincase.

[DAVE BRADY]

Hi,

Is there a seal fitted?

The early ones with no seal tended to get engine oil in to the primary and it was necessary to check the level and drain accordingly.

Dave.

[V500]

Not a problem with my '51 ST, and the primary isn't a leaker either.
That said, the later seal arrangement is clearly a lot better.

[idie]

The wear I was talking about was engine wear creating more blow back into the sump and blowing oil into the chaincase.

[BrummieJon]

Now I've got my 1953 BSA plunger A10 running I appear to have an oil leak coming from behind the drive side crankcase sprocket..

Sucking eggs and all that, but I don't see how that would be a visible leak to the outside?
Sure it's not the engine breather pipe dripping...as they do?

It's a visible oil leak because I'm running it without the primary cover.... It is most definitely coming from behind the crank duplex sprocket. Surely, if I can't fix it, it will just fill up my primary chain case..

[BrummieJon]

After removing the duplex drive sprocket I see that there is no seal, I also know for a fact that there is no oil slinger shim fitted to the crankshaft inside the engine cases.

The dimensions of the seal I obtained from C&D autps is a snug fit on the sprocket slider and it looks like it will fit the aperture in the engine cases so I'm going to give it a go. Ive been getting a few mixed messages from different quarters about this and all the technical documents I have available and what I've found on the web does not cover any of this arrangement in detail.

All I know is that if I have to leave it without an oil seal of some description, I will have to drain the primary chaincase after every run.

[DAVE BRADY]

Hi,

What is that disc? It looks like an attempt to make a seal.
When the seal from C&Ds is fitted in the case it is likely this disc will no longer fit in place and will be no longer needed.
Please post a photo of the seal fitted in the cases.

Dave.

[BrummieJon]

Hi,

What is that disc? It looks like an attempt to make a seal.
When the seal from C&Ds is fitted in the case it is likely this disc will no longer fit in place and will be no longer needed.
Please post a photo of the seal fitted in the cases.

Dave.

Yes, cheers Dave, I'll try and fit it tomorrow. You are correct, the disc will longer be needed if the seal fits...

[BrummieJon]

Tried fitting the seal this morning, failed.... I tries chamfering the edges of the engine casing apeture, lots of lube and I still couldn't push it home... I think the dimensions are correct but the engine casing does not seem deep enough to house the already tin and flimsy oil seal supplied... Ive distorted it now... Not sure where to go now, try a new seal or out it back together as it was and accept the oil leak.

[DAVE BRADY]

Hi,

The seals do seem a bit flimsy and I have knackered one when trying to press it in.  Ideally, the seal needs to be pressed squarely and may need a bit of a whack.  Not the easiest thing to do when the crank is in the way.
How about if you get another one try making a disc that just fits over the crank and fully covers the seal. Something like 1/2" ply or any wood should do. With this pushed on the crank and the sleeve then put on it may be possible to use the crank nut to press the seal in squarely.  A spacer may be needed.
I have not tried this myself but just thought of it now and will keep it mind for the future. 

Dave.