Author Topic: 1946 B31 Crankcase breather  (Read 1779 times)

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Saltydog42

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1946 B31 Crankcase breather
« on: 22 June, 2018, 11:27:04 »
My B31 leaks a lot of oil  from the breather by the the main bearing, plus there are some signs that the crankcase is being pressurised. Is this breather timed or have some sort of valve? basicaly how does it work?. Any information  would be appreciated because apart from a parts book information is hard to come by.
Also would fitting a later breather on the timing case help.
Cheers
Barry

ANDY HIGHAM

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Re: 1946 B31 Crankcase breather
« Reply #1 on: 22 June, 2018, 13:42:25 »
The later flapper valve breather is better but way from perfect. On my B31 I have fitted the reed valve breather from a Yamaha XS650
https://www.heidentuning.com/xs650-shop/fuel-system/air-filters-fuel-filters-carb-holders/crankcase-ventilation-valve-reed-type-detail.html

ANDY HIGHAM

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Re: 1946 B31 Crankcase breather
« Reply #2 on: 22 June, 2018, 13:53:02 »

Saltydog42

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Re: 1946 B31 Crankcase breather
« Reply #3 on: 22 June, 2018, 13:53:49 »
Thanks Andy that looks like the answer, did you use the existing tapping on the timing cover?
As mine has no existing breather would I be better to  fit it there or perhaps further away from any oil?

Barry

ANDY HIGHAM

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Re: 1946 B31 Crankcase breather
« Reply #4 on: 22 June, 2018, 14:01:01 »
I used the timing cover tapping and made a fitting with a stand pipe on the inside. As you do not have this cover I would try putting a fitting in the tappet inspection cover. No permanent modification to the engine

Saltydog42

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Re: 1946 B31 Crankcase breather
« Reply #5 on: 22 June, 2018, 14:16:57 »
OK Thanks i will look into that
Thank you for your help
Barry