How much is too much

[EMS]

This is quite an interesting theory and probably holds some truth, especially for racing applications. But the main reason for setting the clearances on the "wide" side is that the valve will "move" itself into the seat with time and such create a tighter clearance which could cause problems, especially if they are set on the very low end of the tolerances.

[portalespeanut]

Perhaps Mike Nixon might chime in on this, but staying on the loose side of spec will also help compression. See his very good website - 'the motorcycle project'.