Crankcase breather test

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

Postby Oggers » Wed Mar 20, 2019 8:28 am

Chaps

Leaking oil from casings etc. and just want to ascertain if the crankcase breather is working as it should. I believe it located on drive side on the drilled crankshaft end for the drive pinion? Some sort of diaphragm?

Seems to leak from the top side of the vv timing gear cover - the large 3 lobed thing on the offside. Any tips - apart from pull it off, check flatness, clean up, replace gasket, maybe sealant of some sort....The thing is newly rebuilt - not well it seems.....

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Re: Crankcase breather test

Postby Mick D » Wed Mar 20, 2019 8:46 am

Hi

Yes, the breather is as you describe but before looking into that I'd whip off the timing cover and check the mating faces for defects, rectify any found, I'm not sure a gasket is fitted here but if it is replace it and re-seal using Wellseal.
If there's no gasket by design I'd be tempted to make one if the faces are below par.

Regards Mick

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Re: Crankcase breather test

Postby Oggers » Wed Mar 20, 2019 10:48 am

Hi Mick

My thinking is that if the breather isn't functioning, then blow back from the crankcase can force the oil through places it ought not to. I guess as it is reasonably simple to pull off the cover that may not be a bad place to start, but then again I may not be solving the root cause.

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Re: Crankcase breather test

Postby Mick D » Wed Mar 20, 2019 10:55 am

Hi Oggers

Can't fault you logic but if the breather was blocked you might expect to see a smoky exhaust from oil being pushed past the rings - if the timing cover joint looks good then I'd look inside the primary drive.

Regards Mick

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Re: Crankcase breather test

Postby Oggers » Wed Mar 20, 2019 1:03 pm

Aye Mick - Primary drive pressed steel casing is next on the list!

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