[Healeys] Valve gap theory : BN2

[Greg Lemon]

You get a little more valve lift (like having a slightly hotter cam) if you 
tighten the gap.  However, as things heat up and the metal expands you may 
not get the valve to close all the way, and hot gas will get by and burn the 
valve.  I have never read anything suggesting you should tighten the 
clearances up for a little more performance, the very limited benefit is no 
doubt not worth the very real risk of the burned valve.

Greg Lemon