Author Topic: oil coming out of crankcase breather  (Read 7986 times)

Offline Ted_Flash

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Re: oil coming out of crankcase breather
« Reply #15 on: 01.06. 2012 15:23 »
I'm resurrecting this thread as I've just found the cause of my A10 throwing oil out of the crankcase breather in quantities enough to slather all over the back tyre dangerously.  Any comments on the likely root cause or on my proposed fix would be welcome.

The engine doesn't smoke especially badly and a borrowed compression tester showed both cylinders the same and OK.  I checked the breather top hat/cork and all fine.  However when the barrels were taken off, I found I could get a 2 thou feeler gauge into the joint between the two crankcase halves where the breather gallery crosses into the left crankcase-half.  The nut in the crankcase mouth was not 100% tight, though not loose by any means.  I loosened it off completely and the feeler would go right into the joint.  Conclusion - oil is being blown into the joint, thence into the breather gallery and out via chain onto the tyre.

I know I should split the crankcases and do a proper engineering fix with an 'o' ring....however I intend: washing out the joint with thinners, get as much sealant as I can into the joint (using some low viscosity Samsonal sealant), tighten up the crankcase mouth nut very tight (with flat washer and loctite on threads), clean excess sealant off.

Any downsides I've not thought of?


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Ted Wilkinson, Ramsbottom, Lancashire
1950 Golden Flash

Online BSA_54A10

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Re: oil coming out of crankcase breather
« Reply #16 on: 02.06. 2012 01:01 »
When this "suddenly" starts to happen then there is a 99% chance of the sump return tube being blocked.
Next culprit is the cork washer on the breather going hard or breaking up.
Solutions are in the previous posts
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Bike Beesa
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Offline DazSeaton

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Re: oil coming out of crankcase breather
« Reply #17 on: 29.05. 2013 21:59 »
I eventually found the cause of my severe breather oil leak. When stripping the timing covers off i noticed the inner timing cover gasket had not seated properly and was obstructing the oilway on the inner timing cover to the breather and cork gasket. Thus when the engine got warm the breather would get hot and leak oil. Either that or the previous cork gasket I had recently fitted was a duff one. Just something else to check if your having problems.
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If you don't start, I'm going to give you a damn good thrashing!!!

1959 BSA Super Rocket 650
2007 Suzuki Bandit 1250 SA