AJS & Matchless Owners Club

Some good points Gents,
I fitted a solid copper gasket and am a long way down the road with measuring gap to gasket but thanks. I'll double check the valve clearances again because on reassembly of head the inlet was too tight strangely enough. The difference is I fitted a copper compared to composite gasket, is the copper possibly not as thick as a comp?
The carb was the first thing I sorted/replaced some time ago that should be ok, I don't trust anything anymore.
Valves.

Well I removed and checked the pilot jet, OK. Then ensured the push rods have enough play, engine doesn't run long enough to change any tolerances. Started and down to a very fast tickover then same again engine out after about 20 secs.
Looking through the plug hole I see the cyl wall looks wet and the plug also. Not copious amount of oil which is why I honed and fitted rings but wet. I just wonder is the cyl oval and oil is killing the spark the only recourse being a rebore. But there is no smoke when running.

Or is could somehow be fuel supply I should check if the tickler will flood immediately after eng cut out.
Anybody want to buy a G5.

Obviously there should be oil on the cylinder wall but you say there's no smoke when running so have you determined whether the plug is wet with oil or wet with petrol?
There may be a partial blockage or restriction in the pipe from tank to carb. It'd be worth disconnecting the fuel pipe at the carb and see if fuel runs out freely when you turn the tank tap on.

I guess I'm fixated on this oil in cylinder thing, there's only an oil shininess say on the wall so I'll say that's ok. The plug has a wetness which is black and think it's oil but not much.
I have just fitted new hoses and filter. I'll check the fuel flow.

Fuel to carb checked ok. Head off AGAIN reveals positive changes to previous symptoms. Cylinder no longer swimming in oil just light film but oiled plug. No longer exhaust smoke or oil forced out at exhaust pipe to head. Engine ran over a minute with revs instead of 20 secs.
So what have I done in the meantime? Honed barrel, new rings, Cu gasket with Viton seal.
The under and upper surface of the gasket are still covered in oil and compression is only 87psi. I'm now convinced oil is coming across the top and believe the spigot is bottoming. Dimensions: Cu gasket 0.046" (1.18) head/cyl 0.028"(0.7) crush effect 0.018" (0.48) .
I'm think the ppo (po gave up) may of had the head skimmed. Head true flat I will check again but I'm thinking 0.5mm machine off the spigot.
Advise accepted eagerly.

First of all, I know very little on this but I seem to recall someone else with a bottoming spigot simply filing it!

Would annealing the gasket shown, and another, and fitting two gaskets give you the answer?

I know this sounds mad and not for a permanent resolution but if it works it's a lot easier way of being certain and then taking action?

Johnny B

What is the depth of the recess in the head? it should be 0.075" (1.88mm) +/- a couple of thou, this will give you an idea how much, if anything, was removed from it. 0.018" crush on the gasket seems ok, it only moves a few thou on compression, is the head absolutely flat? How much is the inlet valve oiler screw undone by? That piston looks fairly oil washed to me. How much play in the inlet valve stem to guide is there?
MM

Good tech advice gents, thanks. That's practical thinking Johnny fit 2 gaskets, it had crossed my mind and I do have 2x Cu. Can't harm I'll give it a go.
MM. I'll measure the head recess and flat check the head again but the oil can't be coming from the valves because I have previously isolated the oil feed cyl to head and ran the engine briefly, same.
Either one of your suggestions should tell me if the spigot needs filing.
Will go quiet for 3 weeks as I'm away.

Well, I'm not a total muppet but this G5 has got me beaten. I cannot get the head to seal. I have filed the spigot down 0.7mm to 2.0mm gives a gasket crush of 1.13. Fitted Cu gasket (2x together) or composite. Trued up the head with grinding paste on glass. Honed the barrel and new rings and even checked the head bolts aren't, bottoming. I can't get a feelers in anywhere when it's torqued down and I'm only nipping up the 5th bolt which has an m8 helicoil fitted. Nothing has changed. A shame because it starts and ru s great......for 1 minute.

I've had the head off more times than I care to think. The oil has to be originating from the barrel to head feed. The compression stroke will distort a composite gasket (see pic from 2yrs ago when bought) when fitted away from the spigot and suck oil into the cylinder on induction. Which means of course with a Cu gasket is not closing the head to barrel. Warped head or even barrel?

If any member can recommend a suitable engineer near Chester or is willing to let me try the head from their lightweight if it's on winter strip down I'd be indebted. The only way now is process of elimination I would be willing to travel with trailer

Just rethinking this, is the crank case sump still getting full of oil? I am just thinking that maybe the oilway from the crank case back to the oil pump is blocked or the oil pump is not scavenging properly, this would possibly cause too much oil to be flung around by the flywheels and will find itself into the cylinder. It will naturally scavenge but not very effectively.