Pumping oil

Information relating to the Matchless G12 or AJS Model 31 650cc twin
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Pumping oil

Postby bob121 » Fri May 18, 2018 4:10 pm

Dave sorted oil pump while the mag was being sorted. Got them both back onto the bike and fired it up to continue with the fettling. Next day found a small patch of oil underneath the bike. Eventually worked out that it's pumping oil through the crank bolt. Finally had a chance to look at it today. The bolt is a new replacement and has a disc that floats back and forth. The bolt that was in the engine has a ball and spring. Not been able to find any suitable images to work out what's what. Is the new one correct, or is something a miss.
1960 model 31 deluxe.

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Re: Pumping oil

Postby Duncan » Fri May 18, 2018 5:18 pm

Hi Jason

Are these the parts?

1960 Nuts.PNG


1960 List.PNG


The loose flap should seal when the crankcase is pressurised (pistons travelling down) and let air in when the engine is on the compression/exhaust stroke with the pistons travelling upwards, you should not get any significant oil through it. (EDIT - this description is the wrong way round, sorry for any confusion :oops: )

Is the oil coming from the engine breather behind the primary chaincase?
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Re: Pumping oil

Postby bob121 » Fri May 18, 2018 5:32 pm

I'd say it's 025526. I have taken a couple of pictures, but haven't worked out how to load them up. But what I have noticed when the disc is out (down stroke) there's a gap visible behind it. And when in (up stroke) it would appear to close the passage. Fairly certain that it is pumping through the bolt. To be sure, I'll have to reassemble it with the case off and run it up again.

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Re: Pumping oil

Postby les ward » Fri May 18, 2018 7:17 pm

How long has it been left standing. Over time the sump will gradually fill with oil (wet sumping). Try draining the oil from the sump and then see if it still happens.

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Re: Pumping oil

Postby numbersix » Sat May 19, 2018 8:16 am

"The loose flap should seal when the crankcase is pressurised (pistons travelling down) and let air in when the engine is on the compression/exhaust stroke with the pistons travelling upwards, you should not get any significant oil through it."


I'm new to AMC bikes, but I do have experience of how breathers work and I am a bit confused about the operation of the valve.

If it closes when the pistons are descending, then the crankcase will be pressurised, surely? Then, if it opens when the pistons are ascending, it will draw air into the crankcases.

In my experience, a breather's function is to expel the compressed air beneath the pistons and, as far as is possible, not allow it to suck any more in as the pistons ascend.

Or am I missing something? :?
Allan.

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Re: Pumping oil

Postby bob121 » Sat May 19, 2018 4:05 pm

Not wet sumping any more. Pump has been sorted. Spoke to dave and have a few things to look at. Hopefully next week. It needs to be on the road now.

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Re: Pumping oil

Postby Duncan » Sat May 19, 2018 6:38 pm

I'm new to AMC bikes, but I do have experience of how breathers work and I am a bit confused about the operation of the valve.


Allan, you are missing nothing and I am a complete numpty and typed the description the wrong way round, I have no other excuse other than incompetency.

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Re: Pumping oil

Postby numbersix » Sun May 20, 2018 8:10 am

Hi Duncan. Please don't berate yourself! I'm grateful for your reply because it confirmed that I wasn't having a 'senior moment!' :D
Allan.

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