The hardened valve caps were only used on pre and wartime engines, as the valve stems themselves were not hardened, and started mushrooming, when not using the caps.
If you have later valves fitted, they have hardened valve stems,and are a little longer too, to compensate for not needing the caps!
So check what valves you have first, before doing a repair that might not be needed!!
Thanks Lex These valves are in very good condition the inlet has polished up well, There is no mushrooming on the ends after a couple of thousand miles, I recon the later valves have been fitted, will have a check against a pair of new valves I have somewhere, Andrew.h.
The valves in the existing head are shorter than my new ones, have found two valve stem caps so going to fit them tonight.dont think it will do any harm , then its for a start up, Going to sort out a bike for normandy Sunday, somthing with paniers ,a BSA M20 I think Andrew.h.