Oil filling crankcase

Information relating to the Matchless G12 or AJS Model 31 650cc twin
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Re: Oil filling crankcase

Postby Dale » Wed Oct 30, 2019 12:16 pm

Hi Dave,
No, I don't have another pump I'm afraid. I have closely inspected the pumps and there doesn't appear to be any significant wear on the gears. Is there anything I should be looking for?
Dale

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Re: Oil filling crankcase

Postby Dale » Wed Oct 30, 2019 3:35 pm

I have just removed the return pump body again and pumped oil into the oil way with an oil can. The oil came out of the crankcase drain hole (which was previously drained overnight), so it would appear that this is not the problem. I have also put new gaskets under each pump body. I noticed that there was no tiny bleed hole in the feed pump mounting base, although the feed pump is drilled for one. Is this correct?

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Re: Oil filling crankcase

Postby Bird dog » Wed Oct 30, 2019 5:57 pm

At each stage of re-assembly fill the oilways with fresh engine oil to help with priming, I would also consider filling the return pipe to the oil tank as an extra precaution.

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Re: Oil filling crankcase

Postby Bird dog » Wed Oct 30, 2019 6:08 pm

Re the pump condition. In my experience with hydraulic gear pumps similar to our AMC types the wear that reduces efficiency is found on the side plates not so much in the gear cavity itself or the gears.
The plates can be restored by facing off over a piece of fine wet and dry placed over a flat surface and rotated in a figure of eight motion.

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Re: Oil filling crankcase

Postby Bird dog » Wed Oct 30, 2019 6:26 pm

I found this on the web copied from Groily's response to another Matchless owners Club member with pump issues. He refers to the drilling between the two pumps as a priming device.
Testing Twin Oil Pump
by Groily » Mon Nov 22, 2010 9:54 am
Ian, you can take them to bits to see whether:
the drive arrangements are sound;
any teeth are broken;
the gears fit well on their spindles and mesh well;
there is not too much end play on the spindles (there does have to be a bit) and that the end-plates fit flush on the bodies;
and to replace the gaskets at the rear of the pumps inside the mounting plate.
You can also get the screw-in plug out of the end of the mounting plate and clean the cross drilling that primes the return pump from the feed.
A bit of flat glass and grinding paste can flatten worn plates, and new bushings can be made up to replace worn spindle mounts, but it's all a bit of a fiddle.
The age-old teaser 'is it really worn out or are they all like this?' can only really be answered by knowing all the dimensions and clearances (which I don't), by comparison with known good pumps, or by sending the things to someone who really does know for proper overhaul.
Although they look delicate, and there are all the debates here and elsewhere about whether they are up to the job, I reckon they're basically OK. Some level of wear is common and the big Q is 'How Much is OK?'. It would be hard to set up an effective test rig on an ordinary amateur bench to prove exactly how good they are or aren't in terms of capacity and flow and leakiness (especially if one doesn't have enough data, enough measuring tools, the ability to get things to operating temperature, etc). If in serious (any!?) doubt it has to be better to spend the money before risking all the other bits, especially a reground crank . . . .

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Re: Oil filling crankcase

Postby JEAN-NOEL » Wed Oct 30, 2019 6:38 pm

Hello Dale,
you have said "the oil returning to the tank was full of bubbles". I was running my bike today, and I was looking at the oïl return in the oil tank : at tick over, no bubbles. Only an oil flow for 2 or 3 second, and air, for 1 second, because the return pump has a third more capacity than the pressure one. Yes, I have fitted a canister oïl filter on the return side. Bubbles in the oil seem to mean that there is an air leak somewhere. But now, you have renewed the gaskets. I hope everything will be okay now.
Kind regards.

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Re: Oil filling crankcase

Postby ajsph » Wed Oct 30, 2019 6:48 pm

There is a small hole drilled in the feed way in the base plate see picture. Try to blow some air in this hole and see the air is coming out of the small hole in the return part of the base, if not the bleed valve in the end is stuck. The return pump has to be primed with oil from this hole.
Poul
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