Oily AJS twin exhaust

minajs · Post by **minajs** » Sun Jun 26, 2005 9:35 pm

Can anybody help? My 1958 AJS twin is spitting oil. Even after a good, long ride the inside of the pipes are covered in wet black oil. Plugs are always black and sooty. The bike, however, does not smoke, nor is oil consumption heavy. A piston ring problem? According to seller the bike had a rebore just before I bought it, less than 500 miles ago. Regards Michael.

Michael · Post by **Michael** » Mon Jun 27, 2005 7:39 am

Hello, Michael.

Piston rings and reboring were my first thoughts also.

Maybe the oil comes through the valves ? Maybe the valve guide is worn and the oil comes out of the rocker box.
Does the 2 cylinder engine also have got a valve (like the singles) to adjust the oil feed to the inlet valve ? If so close the valve a little bit.

Maybe you should try a hotter spark first. (Talking about NGK that means a lower number)

Michael

paul knapp · Post by **paul knapp** » Mon Jun 27, 2005 5:08 pm

G'Day Michael,Does not sound good! With out pulling the barrels off you could first check oil grade, too light??. Next, have oil pumps been installed in reverse positions?? Although if this was the case I think you would have oil coming out from a few other places as well as the exhaust....Worn big end journals throw excess oil on bores!! Incorrect ring gap and/or incorrect piston groove to ring clearance as well as excess valve to guide clearance or a broken or loose guide all will have to be suspect, you had better get the spanners out. I once purchased an Ariel which had been just rebored with 9 miles on the clock, compression was so so, but I perservered for a few hundred clicks, then I pulled the barrel to discover 60plus thou ring gap. Wrong rings installed by a backyarder. You never know!!
Best of luck
Paul

Biscuit · Post by **Biscuit** » Tue Jun 28, 2005 12:15 am

It would seem to me that all the possible reasons given would cause the bike to smoke like Battersea Power Station. Leave well alone Michael until the thing is run in.

Eric · Post by **Eric** » Tue Jun 28, 2005 12:54 am

Alan has said what I was thinking. If it was re-bored only 500 miles ago its too soon to expect the rings and bore to have become bedded in to each other so wait awhile say 1500/2000 miles before getting to uptight. Unless the pumps are reversed as suggested by Paul the scavenge pump should remove any form of excees that may get into the crankcase becauise of other problems.

paul knapp · Post by **paul knapp** » Tue Jun 28, 2005 9:15 am

G'day again Michael,
As Alan and Eric stated try running the machine in longer. I had this in mind, but having just finished running in my Model 20 twin, I had after an initial 50 miles no oil or smoke whatsoever from the exhaust. I paid particular attention on the assembly of the piston rings, guides and big ends - they are all within factory specifications - and my exhaust boxes are definetely quite dry after 500 miles. In my experiance a new bore with a correctly fitted piston assembly will control the oil right from the word go to the extent of only a slight puff of smoke at gear changes or if the engine is 'blipped' a few times in succession, during initial bedding in of rings for 100-200 miles, definately not pumping to the point of oily boxes. The running in component of a new engine takes longer and is to only enable sliding surfaces to polish and prevent galling and 'pick up' under heavy load of said surfaces. When you first start up after the engine has been stopped for a day or so, look in the oil tank at the oil return from the sump , you should have a continuous stream for a few seconds to maybe thirty , till the excess drained oil has been pumped back, then the flow should revert to a dribble with air bubbles, if it remains a solid stream ,I would suspect over oiling and a fault in the supply/scavenge system. Somebody has not put 2 banger fuel in have they?? Any way, enough of me waffling on! How much can a Koala bear ?! [;)]
Cheers from Paul
Down under

Charles · Post by **Charles** » Wed Jun 29, 2005 11:09 pm

Assuming compression is good then you can probably rule out piston rings. You can't rule out valve guides this way as the seal on compression is between the valves and the seats and not the clearance of valve stem to guide hole.

If you have oil in the pipe but not smoke during running, surely this must be an initial problem on start up only? i.e. it is cold oil being blown through and condensing on cold pipes. This concept would certainly be backed up by overall low oil consumption. If it was a problem of oil getting into the cylinder during running, you would have a smokey exhaust?

So I would look at how oil can get in while it sits idle and I can think of only two reasons, valve guides that leak when cold and let a few drips in over time; cylinder head gaskets sealing on outer edge but not inner thereby letting oil from the channels drain into the cylinders. I would start by the easy option which is well justified on mileage - re-torque the heads down and if that does not cure it, fix a swab to a piece of wire shaped like letter 'J' and insert through plug hole and swab the valve bases after it has sat idle. Extract swab (when it falls off the wire onto piston) with a straight wire with double sided sellotape on the end.

Oil pump pipe reversal would have initiated a seize long ago. Plugs could be running cold so never burn off the initial oily mist so maybe a plug change. I find Champions are superior to the NGK in my twins. Could also be running rich so carbon protects the initial oil which then bleeds through the carbon to make their condition look even worse than it really is - or of course, you could just need to take it for a good blast to clean em off before you stop. It might not fix anything but might well be fun!!

Good luck
Charles

Charles · Post by **Charles** » Wed Jun 29, 2005 11:14 pm

PS - I shoudl have said make sure when it is left idle it is not near compression so if the guides are leaking, the oil does come through and you'll find it with the swab.

Biscuit · Post by **Biscuit** » Thu Jun 30, 2005 9:22 pm

Could it be sooty condensate you are seeing?

paul knapp · Post by **paul knapp** » Fri Jul 01, 2005 3:16 am

G'Day MIchael, once again, Just another thought! The oil in your box's, could it be the left over dregs from the oily engine before it was re-bored, and is slowly working its way out the back with the heat from every ride, giving the impression of fresh oil from the cylinders??
Cheers Paul