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Oil leak for breather?

When I park the bike up after a ride a small pool of oil develops under the bike (wm20). I have eliminate dother sources and am beginning to suspect it comes from the breather pipe. It is not a lot of oil and it does not continue to drip but it does make a mess. Could this be coming from the breather and if so how when the engine has stopped running?

Fortunately quick thinking on the part of a vonuteer at a local hospice avoided us leaving stains on their patio when we visited on Friday. They came out and put incontinence pads under the bikes!

Re: Oil leak for breather?


I hate oil leaks from any of my vehicles, old or new. My M20 was the worst offender.

Some suggestions, from simple to complicated:

1. Make sure it's the breather tube that's leaking oil. Attach an extension tube to the existing breather drain tube and route it where you can see the end. Take another drive and park the bike somewhere appropriate to look for oil drops. Take along an incontinence pad if needed.

2. Disassemble and clean the internal parts of the breather assembly to insure it is not fouled by oil or grime that would prevent it from operating properly. Re-test.

3. Buy a oil catch tank and hook it up to the breather hose. Re-test. I got mine from Ebay, about $20 US and mounted it behind the seat on the left side. See photo link below. I have driven my M20 for about 200 miles with it and no oil leaks so far from the breather. No significant oil accumulation either.

Good Luck on your project.

Dave W.

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Re: Oil leak for breather?

These bikes were not oil tight from new so why try to make them oil tight now that are pushing 80 years old ?
Keep a rag in a convienant place & place it under the bike.
The breather will blow onto the bike and the oily mist deposited will eventually join together and make a drip.
So it is just a case of finding a responsibe place to park where the dripping oil will not be a problem .
It can will leak from the mainshaft sleeve gear .
It can & will leak from the chaincase sliding plate
It can & will leak from the footpeg sleeve
It can & will leak from the inner & outer joint unless you have done a lot of joint work.
It can & will leak from the gearchange & kickstart shafts .

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Re: Oil leak for breather?

Dave - thanks for your tips and the link to the oil catcher. I will attach an extension pipe so the end is visible and I can check that is the source.
Trevor - I quite agree with the sentiment of your post, although parking 'responsibly' is more often a chellenge than not round here. I suppose I should feel chuffed that I don't have leaks from all the places you list. Of the several BSAs I have only one doesn't leak oil and I keep it handy by the kitchen door. Its a Meteor and does pidgeon deterent duties.

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