Head gasket blowing

[RidgebackMotorbike]

Hi,

The head gasket on my AJS 16 1959, was blowing on the spark plug side of the head gasket, so I bought a replacement copper gasket, annealed it and tightened the head back down. I also replaced the rubber tubes and O rings in the push rod tubes (They came with the gasket set) but don't recall seeing any washers when I remove the old rubber tubes from the push rod tube. I read on the forum that the could cause a problem with the headed gasket blowing.

Unfortunately, the replacement head gasket, it is still leaking on the spark plug side of the head. I tried tightening the head down a bit more but it has made no difference. Having read on the forum that this can cause a problem I am now wondering this is being caused by missing washers on the push road tubes or if the head is warped?

If I understand correctly there are two washers ether side of the rubber tube?

I guess I need to start by removing the head and checking/including the washers, replacing the head gasket and seeing if this cures the problem?

Any other ideas or suggestion please?

[g80csp11]

look at the spares list drawings to check
if it leaking either incorrect assembly making pushrod tube too long

http://archives.jampot.dk/book/Spares_l ... _twins.pdf

[Joker_Bones]

Yes... There is a flat washer above the rubber seal, this often remains stuck in the head and it's not immediately obvious it's there. A shaped washer sits on the shoulder of the push rod tube below the rubber seal.

IMG_20230806_150759.jpg

[Joker_Bones]

If the rubber seals are too long... as the head is tightened down the push rod tubes can crush the bottom o rings and bottom out on the crankcase offering resistance to the head being pulled down. The times I have done this I have always ended up shortening the the top rubber seals so that you get some squish on the the bottom o rings but not too much.

IMG_20230807_145939.jpg

[SPRIDDLER]

1952 onward uses B and C either side of the rubber sleeve, plus the rubber 'O' ring at the bottom.

Pushrod tube washers and seals.JPG

Pushrod tubes should be free to move a bit.......

100_1412.jpg

Pushrods should move a tad (640x480).jpg

[Joker_Bones]

This is a '59 m16 head. When I assembled the engine I did not pay enough attention to the mating surface and it was blowing a little and weeping oil around the head gasket.
So it had to come back off... Inked up with a permenant marker and flatted a little on a sheet of abrasive paper taped to a flat surface plate revealed that it was not warped as such but was recessed alongside the head bolt holes

IMG_20221102_184237.jpg

[Joker_Bones]

Some more flatting off to lose the recesses solved the problem.

IMG_20220506_202656~2.jpg

[MatthewC]

Good work, just be careful to make sure it doesn't bottom out on the spigot instead of compressing the head gasket, which can happen if too much material is removed from the gasket face. From what I've seen that recessing around the bolt holes is typical of overtightening of the cylinder head bolts. Unfortunately the torque figure the factory specified on page 78 of the workshop manual (35 lb.ft) is enough to warp the heads in a 4 pointed pattern (worse around the bolt holes) and also to crush the bosses the bolts bear on. After some experimentation I wouldn't exceed 25 lb.ft which in practice is more than adequate even when ridden hard, and I suspect the optimum is a little lower. I've been meaning to write an article for the magazine about it for several years, but never got around to it. Interestingly, I've noticed that the condition of the gasket faces on the later heads (for shorter pushrod tubes) is almost always worse than that of the earlier heads. I've long wondered whether the accountants asked for a cheaper grade of aluminium alloy around that time.

[Joker_Bones]

Interesting...
I've just put together and fitted a G80 engine with an ally barrel and through head studs.
I'd heard/read somewhere that 35 lb.ft was overkill for the head bolts.
So I did them up to 25 lb.ft... The next day I wondered if that was enough and tweaked them up to 30 lb.ft.
It's not been run yet, I'll have to wait and see.

[MatthewC]

You may well find that if you try retorquing the bolts after running the bike for a few miles at least one of them goes a bit further, most likely the one nearest the exhaust port. This seems to be almost entirely due to the head itself crushing, much less the gasket. With lower torque there's much less, if any change. At 25 lb.ft I had that one bolt budge just slightly when checked after 100 miles, and none of them moved when subsequently checked. The next time I put my engine (350cc) back together I'm going to try 22-23 lb.ft, I suspect this will prove to be about right. The last time I had the head off is when I tried 25 lb.ft, I'd have to check the exact mileage but I think it was over 15k miles with not the slightest sign of head gasket trouble, the head wasn't taken off for that reason, but as part of a restoration. When I did have head gasket trouble it was with more torque.