Having blown out several composite gaskets, I intend going back to copper (even if there is oil seepage!). What is the optimum thickness for use with an iron head Dominator 88? . I have seen from 1 to 5mm. advertised? The aim is not to decrease compression, just fed up with removing the head! (and yes, the head is tightened down, at 50, and 500 miles after fitting). Suggestions gratefully received.
If you go above 2mm of thickness then there are likely to be issues with valve clearance.
You will also find trying to anneal a thick copper gasket evenly quite difficult. If you under-heat the gasket then it won't soften enough all over and the combination of hard and soft spots will lead to seepage. If you overcook solid copper gaskets then the thinner sections around the bolt holes will vapourise and go thin and leak. I had an RGM solid copper gasket which I tried on three different engines and each one blew oil sideways.
Possible reasons that your composite gaskets dying so quickly...........There are lots of dodgy cheapo versions on the market which split as soon as you torque them down..........The head bolts on your engine may be a fraction too long and are bottoming out before clamping the gasket. You get a similar problem with rubbish collecting at the bottom of the barrel bolt holes. Especially rusty iron barrels that are 60 plus years old.
I suggest obtaining a quality Cylinder Head gasket from a known dealer and then checking all the chunks that hold the head in place. Add a thin washer tor each head bolt as a means of preventing them from bottoming out.
Its a choice between the oil tightness of the composite but with a low rate of failure but the failure being catastrophic ie cannot continue except on a recovery truck, or a higher risk failure with copper but that being a slow oil leak and the ability to continue.
Can't comment on the right thickness but with a copper head gasket it pays to use copper wire or silk thread around the known leak points coated in a sealant.
There are other tricks like using a copper spray or a silver paint on the gasket, other option is Pliobond which is a glue and works well.
Worth a read
Thanks John Shorter for raising the subject - I feel your pain - and those responding with thoughts on a cure. Haven't suffered this problem for years but a recent build using a 'composite' (aluminium?) gasket lasted just a few hundred miles. Same torque-down method I've used for years - 650ss owned since late '70s - and all threads are sound. I like the idea of a slower failure but some further research is needed before I decide on a rebuild method. Just not this one!
I guess you have had the head and barrel mating faces checked for flatness? Pretty obvious I know, but thought I would mention it, as I had my 650SS head checked some while back, and it was badly in need of a skim. I don't like those composite gaskets, but it is holding so far since then.
There are a couple of points that need a mention with regard to skimming Norton Twin cylinder heads.
1. Most engineering shops that can offer this option generally state a minimum cut of 20 thou will take place. This may not sound much but it can really mess up the rocker angle and valve clearance adjustment. Especially if the valves are recessed into the pockets.
2. If the barrel still has spigots then the head will end up sitting on top of these rather than the gasket. The only cure being to remove the a portion or all of the spigots or fit a massively thick solid copper gasket.
If the head is not flat then it needs attending to, and understanding the knock-on effects of such work is all part of it. My spigots were removed at the same time, as the bore is + 0.040", and they were cracked. The barrel was also lightly skimmed, as it too was not flat. So yes, whilst attending to the head, one would also check the barrel, and reduce the height of spigots as required.
In theory one can adjust the length of the pushrods, (which I have done) provided you can get the ends off, which are pressed on. The pushrods can then be shortened to suit, before pressing the ends back on. Or, you can buy over-length pushrods with only one end installed, allowing you to cut them to length before pressing the end on. They are the tubular steel ones though, and very heavy, so a last resort, in my view.
Follow up:- After fitting a copper gasket, I have just returned from the Spanish Teruel Rally.
Over 400 mile of hard riding ( on my ´54 Dominator ), keeping up with Commandos. The faintest hint of oil weeping from the head. No more composite gaskets for me!