G9 (1954 ). Oil leak

Information relating to the Matchless G9 or AJS Model 20 500cc twin
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G9 (1954 ). Oil leak

Postby allanmg9 » Sun Apr 02, 2017 6:37 pm

Help please, I drained the wetsumped oil from the sump , topped up the oil tank and started the engine , checked for oil return which was fine after a few seconds . All seemed good no smoke and running nicely then realised a large pool of oil forming on the floor from the primary chaincase level , I could actually see the tank oil level going down . What has gone wrong ?. Grateful for any suggestions from you ,

Thanks Allan.

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Re: G9 (1954 ). Oil leak

Postby ajscomboman » Sun Apr 02, 2017 6:53 pm

Crankshaft breather diaphragm stuck open at a guess.

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Re: G9 (1954 ). Oil leak

Postby robcurrie » Tue Apr 04, 2017 2:31 am

When the engine wetsumps, it can also overflow into the primary chaincase, so this should be drained to the correct level as well. If you see the oil level in the tank keeps dropping, it could be the scavange side of the oil pump is not keeping up with the feed side, this could either be the pumps are incorrectly installed or connected or the scavange pump is not working. How long has this been happening, or what has been done recently?

Rob C

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Re: G9 (1954 ). Oil leak

Postby shifter » Tue Apr 04, 2017 6:49 am

My 20 did the same after sitting in the garage for 23 years drained the sump refilled the tank got her started then the oil starter dripping out the rear of the primary case. Stood and scratched my head pondering then drained the primary case refilled to level and after a little run checked it all nice and dry and still the same after many miles.
?

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Re: G9 (1954 ). Oil leak

Postby allanmg9 » Tue Apr 04, 2017 10:45 am

thanks to all for your thoughts they are much appreciated , since it would appear that with the bike running oil is circulating back to tank efficiently. but the level is reducing rapidly as well with oil running from my primary chaincase . I am inclined to think that the stuck diaphragm is a likely candidate . ( The bike does wet sump normally but not too badly .) IT looks like I will have to split my nice oiltight primary bath chain case and have a look at the spring and diaphragm in the breather. But before that I will order a workshop manual from the spares dept to see if there is a procedure to follow as I am not confident in the mechanical department. So if anybody has any thing to add in the meantime please do so . Note. this is not after a rebuild, the bike was running fine this has happened after the winter lay up .
Thanks again, Allan

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Re: G9 (1954 ). Oil leak

Postby dave16mct » Tue Apr 04, 2017 1:31 pm

Don't park it for long periods on the side stand or the primary chaincase will fill up with oil. Also the primary chaincase oil level should only just touch the very bottom of the chain. Always run the engine before topping up with oil.
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Re: G9 (1954 ). Oil leak

Postby shifter » Sat May 27, 2017 4:06 am

Has the oil tank been overfilled, when the oil heats up when running its being chucked out of the overflow pipe ? the overflow pipe on my bike is directed towards the chain (primary area) as we all know a little oil can appear to look a lot more, just a thought
?

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Re: G9 (1954 ). Oil leak

Postby rump » Sat Oct 21, 2017 10:49 pm

I had the same trouble you can have a new spacer behind engine sprocket the one with the spirals that screws the oil from between spacer and sump back into sump the new slinger will need to he made over size to fit in with just clearance in sump.If you cannot do that their is a seal on the market that just fits the sump size a new spacer needs making in place of the slinger and it will only be about one eighth thick.I played with the breather it only works at idle the disk can only move at a limited speed and can not match the rpm increase some people dont use breath disk. rump australia.

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