Crankcase breather

Information relating to the Matchless G9 or AJS Model 20 500cc twin
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Crankcase breather

Postby sunalp2 » Sat Sep 22, 2018 8:30 am

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 11:26 am, edited 1 time in total.

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Re: Crankcase breather

Postby petert120r » Sat Sep 22, 2018 8:52 am

It's a flap valve inside the large nut securing the primary sprocket to the crankshaft

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Re: Crankcase breather

Postby dave16mct » Sat Sep 22, 2018 9:22 am

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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Re: Crankcase breather

Postby sunalp2 » Sat Sep 22, 2018 9:34 am

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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Re: Crankcase breather

Postby ajscomboman » Sat Sep 22, 2018 10:45 am

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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