Testing Twin Oil Pump

[iandusud]

Hi folks. I'm working on a '57 M20 that a friend bought recently. Having stripped the engine there is evidence of the r/h piston having suffered a seizure and the big end shells have also suffered badly. This all leads to me believing that there has been an oiling failure. It also happens that this bike is fitted with a tap on the oil feed pipe! You all know what I'm thinking, but I think it would be wise to check the oil pump. What is the best way to do this other than rebuild the engine and fire it up!!

Cheers, Ian

[paul knapp]

G'day Ian, a simple strip and inspection of the gears, spindles and cover plates should be sufficient. Highly unlikely that the pump is at fault, as they move a lot of oil very quickly. Apart from some clown leaving the oil feed tap closed, the failure may have been caused by a totally blocked/collapsed oil filter in the feed line or simply running out of oil!

Paul

[Groily]

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 . . . .

You're probably right in thinking that that tap is relevant here if it didn't have a magneto earth switch on it.

[iandusud]

Thanks for the replies guys. My general experience of gear pumps is that they are pretty reliable. I am replacing the oil filter as a matter of course and will inspect the gears for any obvious signs of serious wear. My experience with plain big ends is with a 650 Bonneville I owned many years ago which had a pretty feeble oil pump witnessed by the oil pressure warning light flickering at tickover when the oil was really hot. But even with that in the many tens of thousands of miles I put in on it, in the two engine rebuilds I did I never once had to replace the big end shells which showed absolutely no signs of wear.

I still think that the oil tap is the prime suspect. Those things, when not fitted with kill switch to the ignition, are a disaster waiting to happen. As soon as I saw the one on this bike I put two stickers, one on the tank, the other on the speedo face, saying OIL TAP!

Ian

[wilko]

A friend of mine turned down some 1/8th thick aluminium plates to match the outer diameter pump plates to completely cover the spindles with slightly longer screws for attachment to prevent most of the oil leaking out of the spindles. It completely fixed the wetsumping syndrome.As an experiment for skeptics take off your timing cover and watch the oil trickle out around them overnight.

[wilko]

Skeptics, sceptics!!

[greasemonkey62]

I have a dual purpose oil cut off tap on my 1962 AJS 650 twin but it also has an electrics cut off built into it that cuts off the electrics to the points, so unless it is opened no oil and more importantly no electrics are available so the bike will not start up unless the switch is open. if you forget to open it then after a dozen or so kicks and when the sweat begins to run into your eyes you will remember to open the switch !!!! but importantly no damage can be done to the engine.

[1608]

I like the idea of the additional alloy plate. However, we seen to be getting a bit entrenched with the pump as the problem. There could be many causes of oil starvation, dirty oil, worn centre bearing, clogged or varnished filtre etc.