Oil leak from head gasket

[MalcW]

Hi all. We recently rebuilt a 500 twin engine. Once started up we had a bad oil leak from the dynamo joint, now fixed courtesy of a new cork washer and the aid of a small sash clamp when doing it up.
More worrying was a leak from what at first glance seemed to be from one of the base gaskets, but turned out to be from one of the cylinder heads. Removing both heads revealed that one of the viton 'O' rings was split where it had got slightly caught under the copper head gasket when everything was done up. As well as being split, it was slightly lifting the gasket. We'll never know, but I'm guessing this happened at the 'heads on, jiggle the inlet manifold on, do it all up' stage. I've done it before with no problem, but s there a trick to it? Should I be sticking the gasket an 'O' ring in place with Wellseal or similar? It was all assembled dry, as I've done in the past.

Cheers,

Malc

[1608]

Did you need to remove both heads? Its ok to bolt heads down to a little more than finger tight before fitting the inlet m/fold. Don't forget to aneal the gasket.

[MalcW]

Did you need to remove both heads? Its ok to bolt heads down to a little more than finger tight before fitting the inlet m/fold. Don't forget to aneal the gasket.

It was unclear at the time exactly where the oil was coming from, so we removed both heads. Naturally we removed the rh side first, only to find the problem was on the left... Then again, if we'd done it the other way round we would have wondered how the other side was I guess. Replacement parts have arrived today (thanks yet again Spares Scheme), so it can all go back together. Yes, head gaskets were, and will be, annealed.

Cheers,

Malc

[MalcW]

OK, a little bit confused now. After reassembly everything seemed to be fine for 3 or 4 minutes, then a weep of oil appeared at the barrel base, and we noticed that it was spitting some oil from the front of the head/barrel joint, which suggests a) there was oil there to spit, and b) the head gasket was blowing. Another 3 or 4 minutes later and the spitting stopped. Oil return to the tank was good during all of this. Once everything was cold the following day I checked all of the head bolts, which still showed 22ft/lbs torque.
Any suggestions? Warped head maybe? Copper gaskets too thin?

Cheers,

Malc

[1608]

I initially had similar problems when switching to copper gaskets. The problem was the club supplied gaskets were too thin. I went to AMC and they supplied the correct thickness of gasket. I believe 22lb torque is a little low and usually go to at least 25 to 27lb.
Also, check that the recess in the heads hasn't been reduced due to heads having been skimmed at some time.
good luck

[MalcW]

I initially had similar problems when switching to copper gaskets. The problem was the club supplied gaskets were too thin. I went to AMC and they supplied the correct thickness of gasket. I believe 22lb torque is a little low and usually go to at least 25 to 27lb.
Also, check that the recess in the heads hasn't been reduced due to heads having been skimmed at some time.
good luck

Can I just check - I thought 25ft lbs was for the later engines with 3/8 in studs?

[1608]

I'm just saying thats the torque figure I have used a number of times over the years. I don't believe a couple of lbs makes that much difference.

[g5wqian]

hi malc ;
on my model 30 i have tried copper head gaskets in the past but the ones i had were too thin and the spigots on the barrels touched the heads before the head gasket made contact , the only cylinder sealing was from the contact with spigot and recess in head , i used composite head gaskets and it was fine , the composite gaskets were 1.7mm thick , im still using composite gaskets on heads and use the thicker base gaskets all from the club spares ..

im not sure which crankcases you have but i think there are 2 different cylinder base diameters for the 500cc engines , the later 55 onwards cases having 3" i think same as the 600 engine so i would think the thicker base gaskets are available for at least the later cases ..

if i ever have an oil weep it is from the barrel to head joint .

i have 5/16" studs and i use normal open ended nuts with washers and i use a bit over 22 ft/lbs torque which works fine and pulls the heads down ok.

i think i have seen some using acorn nuts but these could bottom out if not checked that they have sufficient clear threads in them .

i use welseal on most of the paper gaskets but also have some hylotyte red from hylomar which is a good sealant somewhat looking like the old hermatite red but good for water and oil resistance .

i dont think ive ever been oil leak free on mine , it seems to keep it in if i stay below 60mph but if i rev engine high it will make its way out of the cylinder head to barrel joint .

perhaps the ajs/matchless twins have too good an oil pump , i know my pressure is good and when testing it minus the relief valve it did not take much for it to go to 100psi upon increasing revs a little .

hope you get it all sorted .
ian

[MalcW]

Hi Ian

I use composite head gaskets on my 650; apart from the faff of going through the re-torquing process in the early stages I think I prefer them. Good point about the acorn nuts, this bike does have them. I think I might change them for std nuts first, tighten back down to a little over 22ft/lbs and try that (easy option first!). If still no joy, heads off again.
I tend to limit my 650 to about 60mph anyway, as beyond that it all starts sounding a bit frantic, and there's a lot of old metal whirling round in there. It tends to stay pretty oil tight (probably shouldn't have said that...).

Cheers,

Malc