AJS & Matchless Owners Club

Went for my 1st ride on my AJS Model 31 today, oil leaked out of the filler cap (tank not overfilled). I removed the cap to recheck level, replaced it and oil was still leaking out several minutes after the engine had stopped. Couldn't be the tank becoming pressurized as I had removed and replaced the cap. Same thing on my return journey ( about 6 miles each way with an hour or so stop in between. Also before setting off on my return journey I checked the oil return (just started the engine) when I arrived home I checked again with the engine ticking over and nothing seemed to be returning.

Any ideas please?

My first check although it maybe too late ,have you got the feed and return oil pipes crossed, the outside one on the oil tank is the return and should come from the oil Union nearest the gearbox .

Thanks for the reply but, no, the pipes are connected the right way round. There is a spring loaded anti wet sumping valve in the supply line which has not been disturbed and was ok for the previous owner. There is a gauze filter in the supply line which just pushes up into the tank - nothing seems to hold it in place. One end of this appears to have a solid slug in it, I fitted this with the slug uppermost thinking that if it was at the bottom it might block the oil supply pipe.

I also note in the handbook that the oil return should be checked on start up and seems to be saying that this is the only time you will get a good continuous return flow due to the oil in the crankcase.

When I say leaking from the cap it was only a trickle but it was enough over 6 or so miles to put a film of oil on the frame, silencer and a little on the back wheel and tyre.

All the added mods, adding more bits to go wrong, perhaps reducing oil flow making the pump struggle. Take them off and see how the system works how it was before adding the extras. Ever since I started riding bikes, I was told to check the oil level and return, before starting off. I would have thought even more important now the bikes are 60 years older.

If you re - read my post you'll see that I did check the oil return before setting off, it was fine. Only after my ride did it seem to be a problem. As regards mods, as far as I understand the filter is standard. The only mod is the anti wet sumping valve which seems a common and useful mod for a machine which is only going to get occasional use. This valve worked OK for the previous owner and must've been OK before I set off as the oil had a good steady return then. I am thinking of removing the gauze filter though as I have a finer filter in the funnel I use to put the oil in.

To start with I'd bin that spring loaded valve and replace it with a "Dove" tap (he advertises in Jampot). You should always be able to see a return to the tank - a steady flow at start up and more of a spurt at tick over with a warm engine. Check out your oil tank filter as well.

I think I've seen the valve you mean, is it the one with the ignition cut out? I'll take a look. I was thinking of junking the filter so I'll do that first. Thanks for the info on the oil return, that's just what I was wanting to know.

Anyone any ideas why the oil should leak out of the cap, do I just need to buy another cap?

Your oil tank cap should have a cork washer.
Dave

Cheers Dave, it has got one.

The most likely cause is a blocked breather pipe. I suggest you check the breather pipe is not trapped or otherwise obstructed.