Commando head on Atlas

Mark, thanks for responding. Sorry I didn't get back to you straight away, we have been for a short break. My head bolts are 3/8", it's an early Commando head I think. I think I have the answer after reading all the manuals again. The Norton Villiers Manual for the Commando says that all pre 1972 Commando should have the insulating washers fitted, so I've ordered them. The idea of leaving them out was due to a passage in the NOC Commando notes where it stated some Combat engines didn't have them in an attempt to get more "wriggle room" due to the head having been planed, so the geometry of the rockers was wrong and the pushrods didn't meet the valve head correctly. I can confirm this from my own experience, as my first Atlas, many years ago had a Combat head, complete with large "C" stamped on it (why?). Naturally the bottom end was utterly sh*gged and the valve tops looked like cold chisels, where the rockers had been just hitting the edge rather than squarely. They were so bad they wouldn't go through the guides! The Combat headed Commandos should have had the pushrods shortened to restore the geometry, but Norton didn't bother (nor did whoever had "tuned" my original Atlas)! The fix was supposedly a special thick alloy gasket; I tried it and spent most of my time keep tightening the head nuts, it had all the integrity of a Victoria Sponge - not recommended! The idea of leaving out the insulating washers is similarly flawed, especially on the exhaust valves.