Pssst. Don't tell anyone I asked, coz I feel like should know already!!

[Windmill]

Thanks to all for clarification, well aware of reasons for burnt valves - changed hundreds when I was in the trade but some years ago now .  Steve, since there is apparently no need to change mine, I won't measure shims now but when/if they need to be removed will do so just out of interest.    

VSR is obviously a later issue, given leaded petrol prevented it back then I guess. Thanks for the link Rich

Take your point Noel and am quite happy to take the experienced view, just wasn't quite sure what that was. Happy I do now though