AJS & Matchless Owners Club

Chaps

Trying to find out where the leaking oil is coming from on my recently purchased, and allegedly fully rebuilt, 55 G9 and I believe I may have a significant clue! Removed the fill hole cover plate on the side of the primary chaincase and half a pint or so poured out. Sucked the rest out until the level is touching the bottom of the chain, but clearly a root cause needs to be found.

I have a few pointers which clearly require chaincase removal and a thorough check, however any other suggestions would be most welcome. One thought - I did clean out the foam cylindrical oil filter forward of the crankcase, the housing and the non-return valve. I wonder that if I re-assembled incorrectly that this may be a contributory factor. Pretty simple excercise and cannot think where I went wrong......

Probably just let oil down from the tank via the pump - wetsumped - and then it's trickled through into chaincase. They most of them do that sir, if left un-run for a while. Especially if parked on a sidestand.
How much oil still in oil tank . . .?
Wouldn't fill it up if it's very low until the crankcase has been checked for / drained of what's probably lurking in there. Could be a lot. Drain plug is underneath and reasonably accessible. A rebuilt motor might even have a decent hex on the plug!

Loads and loads of threads on here on this, also on forums for all marques with gear oil pumps which let oil gurgle through . . . which is pretty well all of 'em bar Triumphs and some Ariels with piston pumps.

See also threads on fitting inline taps (and why not), on using automatic suction valves (and why not).
I use taps, but many wouldn't, for very good reasons.

Doubt there's anything wrong with your beast - probably just needs to get out and about regularly. Hope that's all it is - it is usually anyway.

Indeed. And there's always the tap with ignition cut-out by micro-switch sold by the good Mr Dove, and advertised in the Jampot. A solid bit of kit, I have one in the shed somewhere.

Further investigation leads to the oil tank, which clearly shows the level has dropped dangerously way down to being able to see the feed pipe outlet - not good.

So, lots of oil finding its way to the chaincase. I'll give it a run out when the weather clears, and then if level in the oil tank has dropped again, time to whip off the chaincase and poke about. A list of prime suspects would be appreciated - I'll start with the breather....

I dont think you have understood the explanation. The oil pump will let oil seep past the gearing when the engine is not used. This drains down to the crankcase and when this is full the oil seeps through main bearings into the chaincase. Leave it on the side stand and it will fill the chaincase quicker. On my twin i can get away with leaving it 10 to 14 days between starting, which then pumps the oil back into the oil tank, so long as i leave it on the centre stand. You will not sort it by poking about in the chaincase.

Hi Oggers

That's 'wet sumping' - as Clive says, caused by oil seeping through the delivery oil pump when standing.
Not a lot can be done to prevent this apart from fitting a stop cock in the delivery line from the oil tank - should you adopt this solution be aware that the first time you forget to turn on the flow you will probably wreck your engine

The problem is worse with a worn oil pump so start your investigation there - not sure if new or reconditioned pumps are available.

Thicker oil will slow the transfer too - do you know what oil you are using?

Regards Mick

Dave reconned the pump on my m31. This has all but eliminated the wet sumping. Dave was doing something in conjunction with someone else. Where he was doing batches of pumps. I think it may have been 'ajscomboman'.

Chaps

I appreciate what goes on with regard to wet sumping and leeching through bearings, however I cannot be certain whether the overfull primary chaincase was as a result of wet sumping when the bike was not used prior to riding it, or it occured when the bike was actaully running - something behind the chaincase leaking when running perhaps?

I guess one way of verifying if wet sumping is occurring perhaps is just undo the sump plug, drain off, replace plug and see if much more flows out after a week or so? with bike on centre stand....

Oil pump seems to work fine enough, good splurge of oil though the return - but admittedly not checked it to see if it passing. The above will verify I guess.

Oil is Castrol classic 20W/50

bob121 wrote:Dave reconned the pump on my m31. This has all but eliminated the wet sumping. Dave was doing something in conjunction with someone else. Where he was doing batches of pumps. I think it may have been 'ajscomboman'.

He is indeed, however he's extremely busy with work at the moment and has done 2 which I've yet to collect. I'm holding on till I have a dozen of them done, however if someone is absolutely desperate for a recon oil pump I can pick them up sooner.