[grahampaul]

hi everyone.
 what gasket sets are you using,got a feeling the heads coming of.

[stinkwheel]

I buy them individually from Hitchcocks. I use the cometic composite head gaskets and a normal base gasket. The others are usually fine to re-use but i keep a spare rocker cover gasket just in case one tears.

[Raymond]

I buy them individually from Hitchcocks. I use the cometic composite head gaskets and a normal base gasket. The others are usually fine to re-use but i keep a spare rocker cover gasket just in case one tears.

Interesting - I was thinking of buying H's copper head gasket, thinking it will be re-useable. Why is the composite one better?

Head is off at the moment while I consider what to do about the scored piston . . .

[Paul W]

I changed to a solid copper head gasket for my iron barrel 350, simply because I was very used to them on my old BSAs. Despite annealing it very thoroughly it I found that it soon developed an oil leak. Took it all apart again and re-annealed it. Some time later it suddenly began leaking again.

I then fitted a modern composite head gasket, like it had from new. No oil leaks since, probably ten thousand miles later.

[stinkwheel]

Interesting - I was thinking of buying H's copper head gasket, thinking it will be re-useable. Why is the composite one better?

If you think about it, the gasket is doing two main things. It's preventing pressure escaping from the barrel and it's preventing oil leaking from the pushrod tunnel (and to a lesser extent, the barrel studs). Getting the correct amount of squish to do both effectively would take a lot of fiddling with spigot heights etc. The composite ones seperate these two functions by having both a fire-ring for sealing compression and a more compressable material with a sealing compound to keep the oil in. In short, I was always getting an oil leak with the more conventional ones and I don't with these.

Downside is you usually need to do a fair bit of scraping when you take the top end off, they are relatively expensive and can't be re-used.

I've seen what seems to me a nicer way of doing it which is to machine a groove round the pushrod tunnels so you can fit o-rings round them. Then plastiguage the spigot and head clearance and fit a copper gasket for the optimum clearance with the pushrod holes enlarged to accommodate the o-rings. Then the head gasket is only sealing pressure and the o-rings are sealing the oil, both things doing what they are best suited to do. Seems like a lot of work though and I'd have to get someone else to do the machining which would mean leaving the bike in bits for a protracted period. Hence composites seem a good halfway house.

[Paul W]

In days long gone by, engines often needed de-coking, mainly due to the lead salts that formed due to leaded petrol. It made more sense to have a re-usable copper gasket. With modern fuels, everything stays much cleaner so engines should go for much longer mileages without needing a top end overhaul….in theory, anyway.

[Raymond]

Thank you All for those explanations. Think I'll go for composite, then.

[AzCal Retred]

This is optimal like Stinkwheel said. "I've seen what seems to me a nicer way of doing it which is to machine a groove round the pushrod tunnels so you can fit o-rings round them. Then plastiguage the spigot and head clearance and fit a copper gasket for the optimum clearance with the pushrod holes enlarged to accommodate the o-rings. Then the head gasket is only sealing pressure and the o-rings are sealing the oil, both things doing what they are best suited to do. Seems like a lot of work though and I'd have to get someone else to do the machining which would mean leaving the bike in bits for a protracted period. Hence composites seem a good halfway house."

As SW points out, there are two entirely different jobs happening with the head gasket. The spigot height and head recess determine success or failure. The composite generally leaves a gap between spigot and head which eventually fills in around the spigot with hard carbon, making the head tough to remove. To me, separating these two functions seems a way more reasonable approach.

What I intend to try next go around is to lap in the cylinder head to the spigot and use "Indian Head Gasket Shellac" to seal it. The pushrod tunnels will get a piece of cork gasketing with a coating of "Moto Seal" or similar. The compressible cork just needs to be a bit thicker than the head/cylinder gap. The Moto Seal is mainly insurance...

[ddavidv]

Composite gasket on mine for...sheesh, I don't know how many years now. No leaks.

[grahampaul]

thanks everyone.
havent annuld a copper gasket in over fifty years, could be amuseing/nostalgic lol
i will go with composite for now.