AJS & Matchless Owners Club

This is a well discussed topic I think? but perhaps an expert out there can help!?. My 1959 G12 has always occasionally overoiled and pushed out clouds of embarrassing smoke, but now it's intolerable. Oil is trickling out the dynamo mount. I've rebuilt the engine five years ago, rebuilt heads with new guides (SRM) last month. Is it possible the pump gears are switched round? If so, how do I check? HELP! (Please) I am a re-joined member so don't have all the recent mags. Does the club do a Tech Tips CDROM ? I will now check through some of the postings to search. Thanks anyone. (Bob in Devon)

Hi Bob,

Checking the pumps - remove timing cover, the right hand pump body is the delivery and should have a shorter centre section than the left hand, scavenge, pump or put another way the overall depth of the delivery pump is less than that of the scavenge pump.

Alan is right in a complicated sort of way. The pump near the front of the bike is the delivery pump while that nearer to the rear the return pump. Both pumps are identical in diameter but the return pump at the rear should be thicker than the delivery at the front. This should ensure that the return pump always has more than enough capacity to remove all of the oil put there by the delivery pump. Several things could cause your problem, the pumps maybe around the wrong way, somone may have in the past fitted a return pump in place of the normal delivery to get more oil in are both pumps the same thickness? The return pump cannot suck oil up from the crankcase it has to be primed by a controlled bleed from the delivery pump, this passage could be blocked. The return pump maybe completely worn out or damaged, when working correctly it can suck back quite large bits of debris that would damage the gears. The return oilway from the crankcase maybe restricted by debris or sludge, if you dont already have one the workshop manual obtainable from the spares scheme describes how to check and rectify all of these problems. You say it has got a lot worse since the head overhaul was anything done to the pumps then? Or could you have over done using gasket sealant so this has got down into the crankcase and then the return oilway and pump? All these things are possible. Hope this helps in some way.

Eric - Define 'acomplicated sort of way'

If the problem happens well into a run, then the problem is probably pump related. Try smoothing the mating faces of the pumps and back plate and re-building the assembly using a VERY small amount of "Wellseal". This after you have cleared out all the oil passages, pipes and filters. Check that the non-return valve in the pump carrier has not been disturbed.

If it happens shortly after starting after the machine has been standing, then wet sumping caused by oil flowing under gravity through the pump is probably the problem. The easy solution is to fit an oil tap. Just make sure you don't forget to turn it on when you start up! I have made little signs saying, "oil" which fit onto the throttle twist grip with a spring clip. Try getting your machine out without putting your hand on the twist grip. After a while it becomes as natural as turning on the fuel.

Yes, thank you for the replies. I did find a piece of gasket cement in the return hole in the top of the crankcase when I took the barrels off. I will check the pumps. Thanks again folks, this is a very good forum !