AJS & Matchless Owners Club
Limited

I have not owned a G.80 yet (I'm still putting the money together to buy one), so what I suggest is based on a lot of experience with other Brits (mostly BSA's), but it may help.

I believe the G.80 oil pump is a double plunger type, with one plunger for feed and one for scavenge. The fact that you saw frothing and bubbles in the oil tank, and the sump was oil free, suggests that the scavenge side is working ok, but does not prove that the feed side is working. If the pump is fitted with one-way valves, are they free to move and fitted the right way round?
I would expect the cylinder wall to be lubricated by oil which has passed through the big end bearing flowing onto the surface of the flywheels and being flung off as they rotate, so the cylinder wall is lubricated by a combination of splash and oil mist. If the wall was dry, that suggests that the big end may also have been starved of oil.
A common return route for oil fed to the rocker box is down the push rod tubes, where it lubricates the cams and followers, so it would be worth checking these as well. Hope this does not sound too gloomy, but the speed with which you stopped the engine may well have prevented any major damage. Hope you get more detailed advice from somebody who really knows this motor.

Best regards,

Thanks again for taking time to reply

Safe riding
Tom

Having wiped clean both the piston and the cylinder bore I discovered that there has been metal to metal contact between the two parts. A track almost ½" wide on the piston shows sign of melting whereas the bore seems less hurt. What worries me is that the flywheels are also very dry, so I will take the bottom end apart and check if all bearings are ok! Phew! This is getting scary, but lots of lessons learned!

Safe riding
Tom

another idea has just come to mind for when you put it back together. A friend of mine had a Gold Star which was in a very high state of tune, and after he rebuilt it, he rigged it up with an electric motor driving the engine through a chain and sprocket. I think he used a car windscreen wiper motor and drove it by the sprocket on the drive side crankshaft, but you could probably turn it fast enough to prove the lubrication system with some sort of crank handle bolted onto the clutch. My friend wanted to run the Goldie at a fast tickover for an hour or two with no load on it, just to run it in very gently, but he also wanted to check the lube system, so he left the cylinder head off, and diverted the feed to the rockers into a tin can so he could check that was getting through. He certainly proved that oil was reaching the big end and the cylinder bore. What he hadn't realised was that the compressed gas in the combustion chamber gets down the back of the piston ring grooves and presses the rings out against the wall to form a gas tight seal. But, with no cylinder head fitted, there was no compression and the rings were just floating. He found that he had to keep stopping the engine after a minute or so and wipe the excess oil off the top of the piston crown, or the engine started spraying it all over the garage roof. Fingers crossed that it turns out well for you, anyway.

Best regards,

Safe riding!
Tom