"Stormin Mormon" wrote in message

I took a small engine repair course years ago. To fix this, you have to
take
off the motor cover, the cylinder head, and then remove both valves. Grind
a
little off the bottom, ch eck the clearance, and put it back together.
Requires some specialized tools, and some replacment gaskets.

What makes for less clearance after 4 years of running? I'd have thought
the opposite would happen. Or is it worn on the stem and not contacting
properly so relieving the valve seat brings it back?