Crankcase breather

Information relating to the Matchless G9 or AJS Model 20 500cc twin
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sunalp2
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Joined: Tue Jan 07, 2014 8:11 am
Location: Melbourne AUSTRALIA

Crankcase breather

Post by sunalp2 »

I've done a search, with no results.

Where is the breather located on the model 20 engine?

I have a feeling mine os either blocked, or not working.
Last edited by sunalp2 on Mon Sep 24, 2018 12:26 pm, edited 1 time in total.
petert120r
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Location: POWYS UK

Re: Crankcase breather

Post by petert120r »

It's a flap valve inside the large nut securing the primary sprocket to the crankshaft
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dave16mct
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Location: LANCASHIRE UK

Re: Crankcase breather

Post by dave16mct »

On the earlier twin (1950) like yours it would be a timed breather driven by the inlet camshaft. You should be able to see the rubber tube from it behind the barrel at the back of the chaincase. See page 18 of your 1950 owners manual. You may also have the flapvalve on the end of the crank if the crank has been replaced with a later one.



http://archives.jampot.dk/book/Owners_m ... Manual.pdf

Dave.
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sunalp2
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Joined: Tue Jan 07, 2014 8:11 am
Location: Melbourne AUSTRALIA

Re: Crankcase breather

Post by sunalp2 »

dave16mct wrote:On the earlier twin (1950) like yours it would be a timed breather driven by the inlet camshaft. You should be able to see the rubber tube from it behind the barrel at the back of the chaincase. See page 18 of your 1950 owners manual. You may also have the flapvalve on the end of the crank if the crank has been replaced with a later one.



http://archives.jampot.dk/book/Owners_m ... Manual.pdf

Dave.
Sorry Dave, my signature is a bit misleading. My 1950 18s frame has a 1954 Model 20 motor and gearbox.

The reason I'm asking this question is that I've recently done the oil seal mod to stop oil going into the probary tank, and all of a sudden the engine is blowing smoke.
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ajscomboman
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Location: HAMPSHIRE UK

Re: Crankcase breather

Post by ajscomboman »

Breather on the crankshaft bolt is the first place to look. It is possible the spring loaded flap has jammed as they are flimsy little buggers! Good news is at least they are serviceable and the parts available.
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