AJS & Matchless Owners Club

Hello. I am new to old fantastic English motorbikes and have a1958 600 cc Pan american.

i have a quite heavy oil leakage and I think the crankcase pressure is way to high and that's why it is leaks oil from different places.

It comes quite a lot of oil from the breather hose in the back, Also if I remove one screw on the engine cover on the right side there is also pulsating air and oil mist from there.

Any ideas of what to do without having to break down the engine.

The bike have been standing still for a a couple of years and recently been started up again. Runs ok but smoke comes out from the exhaust pipes so I am suspecting to much blow by?

I would also like to get ideas where to buy a new oil filter that ships to sweden.

Very grateful for replies since my experience of old bikes is limited

Thanks, Martin from Sweden

Hi Martin, I think the Pan American was the name in Sweden given to the model in the UK known as the Matchless G11CS (or AJS model 30CS ?). Assuming it is there should be a crankcase pressure relief valve built into the nut holding the primary drive sprocket on. This then vents into the Primary chaincase. I think it is only a flap valve but if it has rusted or got stuck whilst the bike is standing it could be the problem.
I have two G11CS and one tends to vent oil mist through the breather pipe for the oil tank if it is over filled (the other does not!). When I was building up this bike I managed to obtain an original ex factory new old stock heat cover for the oil tank. This had the original oil level decals on it and the tank was only supposed to be filled to about 3/4 maximum capacity. (sadly they have worn off now but I maybe able to dig out a photo). So have you over filled the tank?
There tends to be a leak of oil around the seal between the dynamo and inner timing side case. This leak can be confused with one from between the crankcases around the oil filter tunnel. There should be a small circular gasket fitted there but to check you have to split the cases. If it is leaking there it will appear to run out below the dynamo.
Finally AMC fitted and didn't fit oil pressure relief valves on models over the years, it is unclear why they did this. My 1958 G11CS was not fitted with one. The oil pressure can get very high when starting from cold and drop to normal levels once the engine is hot. To stop leaks I (or rather a friend) retrofitted the later type (which also required changing the oil filter) and fitted the missing gasket between the crankcases. You might try running on 20/50 oil to see if that helps.

MartinJ_Sweden wrote: ↑Tue Aug 23, 2022 7:27 am The bike have been standing still for a a couple of years and recently been started up again. Runs ok but smoke comes out from the exhaust pipes so I am suspecting to much blow by?

Welcome Martin.
My knowledge of twins is minimal but I would add to Clive's comments that add since the bike has been left unused for a couple of years the piston rings may have seized/become gummed up in their grooves which could account for piston blow-by and excessive c/case pressure.
It's possible that they may free up after a bit of running. Or not

To aid you in becoming familiar with old AMC bikes you can find manuals and spares lists in the archives here under 'Books'

http://archives.jampot.dk/

As the bike had been sitting a long time, you did drain the sump before topping up oil to level?
As above, easy first thought is simply over filling after wet sumping. Would certainly cause symptoms.

hi martin ;
i have a 1956 model 30 , it has an external breather connected to a pipe fitted into the rear rocker cover , using an old modified classic mk1 mini clutch breather , it was all modified by someone in the past and it does not have a crank breather nut because it has got an alternator crank in a dynamo engine and they used other parts .
it does not have a cushdrive , instead has a spacer and nut to hold engine sprocket on .
i have dissaembled an alternator rotor to use as spacer and bought the parts to modify it back to breather .

you can get the crank breather nut from amoc club spares .

check which crank you have and which breather nut .

you can get new 025298 breather nut for 1959 > with alternator or 025526 for 58-61 with dynamo or 016673/4 assembly for 1952-56
pages 5 and 8 in the amoc twin spares list .

https://www.amoc-parts.com//store/comer ... ategory=53

i would suggest before you do anything else , due to time its been standing without running it , to run the engine and let it tick over until the oil has been pumped out of sump and into oil tank .
they do tend to get a bit of oil in the sump if stored for longer periods and i just let my engine pump it back up to tank when i start engine .

the smoke you mention may be a combination of old oil in the exhaust, down the bores and top of piston ,and in the ports in heads , it may well clear up after you have ran and ridden the bike a while .

run N5C plugs in it as they will run hotter and burn off better .

regards
ian