Quote Originally Posted by JohnL View Post
My gut feeling is that it's probably safer to allow the clearances to get too big than too small, hence a larger clearance on a lower perfomance engine with a longer clearance service interval(???).
Nah, you can create too much force smacking the valve cap.
One of my good mates lunched the head on his 450 dirtbike, as valve clearance was out of spec (too large) on one valve. I used to help him with all that stuff, as there is nothing to doing cam swaps and valve clearancesw in these things.
He never got around to replacing the shim that was out of spec, and guess which cap smashed to pieces, in turn dropping the valve into the cylinder and making a mess of things?

My theory is you could throw the valve open, insted of just pushing it open with loose clearances.

I guess that's why they have a lower and upper limit to valve clearance specs.