Thanks for your help Eddie, after what you said about the powder coating I decided to take a bit of time to remove it from the seats before fitting the head back on. Discretion being the better part of valour and all that, (honestly it' s not because its raining cats & dogs) I'm taking it out for a short run, will tighten up, allow to cool then reset the tappets & hopefully all will be ok. See you tomorrow.
Neil