Head gasket

After nearly 70 years of use, The head and / or barrel may have warped. Check this out first.

Next check the head for cracks. A common fault area with early Dominator heads is between the valve seats and also between a valve seat and the spark plug hole.

If the head looks good then next purchase a good quality composite head gasket.  I would not advise a solid copper gasket if the cylinder head is cast Iron. 

Using High temperature sealant is ok as long as it is used sparingly. The area around each of the push rod tunnels generally benefits from some sealant, especially if the gasket eyelet rings do not look too healthy. ie there is a nick or split.

Phil, why would you not recommend a solid copper gasket with a cast iron head? I have a 1936 Model 18 and I fitted a copper gasket, which so far seems to do the job (although it's only done a couple of hundred miles since being installed after fitting a new liner and piston) 

Thanks

John

Next to engine oil.......the choice of head gaskets easily comes a high second with regard to the 'which is best' for my engine argument.

On the Norton Twins you need to anneal the solid Copper gasket and get this procedure dead right. Too much heating and you will burn the metal in the thin areas away and make them thinner. Too little heating and the hard areas stay hard. 

The choice of Copper used for making a solid gasket is also very important. Like Steel and Aluminium there are additives which can change the properties of the finished product.

On the early Dominator engines, the head gaskets are very thin behind the spark plugs. Especially near the head bolts.  Get the annealing in these areas wrong and hot, thin oil will have a quick escape route.

Thanks for the explanation Phil.. for no reason really I've never considered using anything other than copper on any of my machines, singles or twins. Next rebuild I might break with tradition and try a composite one.