AJS & Matchless Owners Club

Before I start to pull down my 56 G80CS i thought I'd open a can of worms and ask for some pointers. On the return journey back to the IWKR campsite the bike started to pump oil out of the decompressor lever in a manner that wouldn't shame the Exxon Valdiz!! It emptied over half the oil tank over 80miles all down the the barrel and rear of the bike. Whilst the motor was running you could see the oil running out the decompressor like a river.

Now either the crankcase breather has decided to jam shut or possibly a compression ring has broken pressurising the upper cylinder. Simple to test the breather by placing my finger over the pipe like wise I can do the same with the decompressor hole by removing it and placing in a rubber bung and wait for it to pop out under the pressure. The o ring on the compressor lever is new. Any other simple tests anyone can think of?

Carry a more tissues with you😂

G15 Roy wrote:Carry a more tissues with you😂

You're not being much help are you! You saw the leak, I'd have to have a pick up truck following me loaded with tissue to avoid an enviromental disaster! Now stop being silly and let some more constructive replies come in!

As you know, oil can only drain from the rocker box by running down the pushrod tubes to the cam chest and then to the c/case. Perhaps as you suspect, there's excessive c/case pressure escaping up the pushrod tubes and pressurising the rocker box due to a broken ring(s) or stuck relief valve .
I've read in one of the F Neill manuals that some singles (and twins) were modded at the factory with a restrictor fitted at the oil delivery point in the rocker box to prevent excess oiling. Could this have become dislodged/fallen out? Mind you, half a tank in 80 miles is extraordinary and suggests that the rocker box is filling with oil rather than c/case pressure forcing just an oily mist out of the decomp lever.
You say the 'O' ring is new. Did you renew it because it leaked there previously? Is it seating correctly and the decompressor arm fully inserted in the rocker box ? (I guess it must be otherwise the decomp cable wouldn't line up with it properly).

How was the bike running when the oil was leaking Rob? If the bike was still running OK no loss of power etc. This should surely rule out some of the points raised. like broken rings, not raised, valve seat rotation. These could cause pressure, but also power loss.

Bike has plenty of compression and does not smoke when running other than pulling away from a standstill.

As it happened so suddenly I suspect a blocked breather and the pressure building up via the pushrod tubes. It was a very impressive sight (NOT) to see my pride and joy literally pumping oil out the decompressor. Tried 2 different O rings Nev and also zip tying the lever in to hold it tight so it didn't push out under pressure and it still pissed out like Niagra Falls!

There's not much else in reality that it can be that could fails so quickly with such dramatic results. As the g/box needs a little fettling I'll pull the primary side and remove the breather. If that reveals nothing then I'll pop the head and barrel to see if a ring has gone.

Hi

It sounds like oil is not returning from the rocker box and once it reaches capacity the oil is being vented from the valve lifter spindle seal, I guess the rate of loss would approximate to the delivery rate to the rockers. Have you done anything recently that could result in a blockage to the return galleries at the bottom of the push rod tubes?

I struggle to see how this could be a breather issue as I don't see what would stop the engine breathing via the drive side bearing and chain case.

First thing I'd do would be to run the bike with the rocker cover removed and observe what happens - if you see oil 'foam' from the rocker tubes it is breathing related, if the tubes just fill up it would indicate a blockage.

Regards Mick

I have seen holes burnt in piston crowns. But the bike only a couple of miles into a run went no further. Cant be fractured oil pipe connection or Rocker box, or it would have been seen. Pressure may not vent via bearing if PO has put sealed for life bearings in, just removing the inner seal.
Look on the bright side Rob, you could be on a winner. 1st to be known to have suffered a particular problem.

Mick D wrote:......if the tubes just fill up it would indicate a blockage.

Steak pie crumbs.

Not touched anything to cause the issue. It's a fully rebuilt motor by Ken De Groome and has run faultlessly for over 1500 miles. I'll pull off the rocker box and see if I can pin point anything up top. I'm not over worried about having to pull it apart but it's weird that it just happened out of the blue!