AJS & Matchless Owners Club

Okay folks, I've finally got my '54 to the point of running reasonably well and the weather was nice enough here to actually let it run for more than a few minutes. Anyways, I'm having a problem of disappearing oil from the tank. The scavenge pump is returning some oil, however it's not enough and as a result the crank case is filling up. This is to the tune of about 1qt in 10 minutes of idle. So... what do I need to check first, second a third?

Firts, check that the feed and scavenge pumps are mounted on the pump carrier plate the right way round. The scavenge is the fatter one.
Second and third . . . folk will be along in a bit . . . and you'll probably get a fourth and fifth as well!
Worth looking out some of the previous threads on here on wet-sumping and poor scavenging too.

It's a single Bill. I've never had wet sumping on a single. Have you tried taking the filter out and seeing if it returns ok with the filter cap removed? Have you got one of the dodgy filters with too much fold over at the top? Are the oilpipes connected the right way round?
Dave

cfaber wrote:..... I picked up a 1954 AJS 18s for next to nothing (£450). The bike is a partial, single owner basket case from the original owner. The bike was stored in a barn from 1964 -> . .......From what I could tell, the engine was seized, though once I got it apart it appeared that the only issue was glue/pitch/seal? that had worked it's way down from the mating surface between cylinder and crank case. This crap was all over the inside of the engine and when I finally got it all apart I couldn't find any mechanical damage, just a sticky big end and a set of RSL8's that need to be replaced.

Going back to your first post from two years ago (above) on acquiring the bike I wonder if there is still some, quote: glue/pitch/seal? unquote, lodged in the crankcase scavenge/return drilling?
If not, there may be an air leak at the pump end plates...........
If you were running it on the side stand maybe the oil is also filling the now oil-tight chaincase as well as the crankcase.......

dave16mct wrote:Have you got one of the dodgy filters with too much fold over at the top? Dave

Yep, that's the first and easiest check to do.

Without any shadow of a doubt I'd lay good money on the return being blocked, your issue is a classic sign that somewhere in the return there is either a bit of piston ring or a build up of sealant goo, usually silicone I find. You can see how good the return is by removing the pipe and starting the engine (making sure you have a full oil tank naturally). Bit messy but a good indicator.

Ha! Eejit, is wot I am. Should read the headings sometimes!! So, yes, partial blockake almost for sure . . .
I'll crawl back into my twin-shaped hole now!

ajscomboman wrote:Without any shadow of a doubt I'd lay good money on the return being blocked, your issue is a classic sign that somewhere in the return there is either a bit of piston ring or a build up of sealant goo, usually silicone I find. You can see how good the return is by removing the pipe and starting the engine (making sure you have a full oil tank naturally). Bit messy but a good indicator.

I've gone through and checked the return line, the pump reciprocation, etc. When I rebuilt the engine I did check that the scavenge feed at the bottom of the sump was clear with an air charge. Without splitting the cases how can I verify it's clear now?

My other thought was that maybe the sump drain bolt was some how blocking the scavenge port, but it's not bottoming out on anything.

This is not neat and tidy, but it is an effective test, and clean up is easy. Since the engine runs and the pump returns “some what”, let's test for an air leak at the head of the scavenge pump.

Assuming a slight air leak, the scavenge pump's effective volume will be reduced with air leaking in, and it's usual volume of oil output diminished.

Start the engine, take a can of wheel bearing grease and coat the scavenge pump plate with a liberal coating of grease covering the entire plate to engine perimeter AND each of the the small hex head screws. I'm not talking artists paint brush, I'm talking table spoon. If the oil return noticeably increases within seconds, the problem has been located.

Frankly, one could probably get the same result with a trigger pump oil gun with heavy oil, but the image of slobbering grease over the entire cover plate helps paint the sealing principle.

To check the scavenge inlet at the bottom of the crankcase, remove the crankcase drain plug, and for your year engine, (if my memory is good), you can run an aircraft length twist drill, thru the drain plug hole up 6 inches or so into the oil pickup gallery. It's about 5/32 or 3/16 ID

Later engines had a separate 5/16x26 slotted oil plug screw providing access to the pick up gallery, and this slotted screw is adjacent to the drain plug. Like 1/2 or less to the rear of the engine, and on the underside.

Drain plug screw can not easily block inlet, and the plug should have a square magnet tightly jammed into it.

Ciao, DC

Hi

Dick's air leak theory is worth investigating but if the leak was significant enough to affect the return flow that much I would expect a substantial oil leak from the plate during the 'pressure' stroke.

Have you checked the basics? - Is the pin correct for the plunger and is it fitted the correct way around, (reduced diameter at the bottom)?

Regards Mick