2002 Yamaha YFM660 Grizzly factory service and repair manual, Page 172Get this manual
VALVES AND VALVE SPRINGS Install
the valve into the cylinder headTurn the valve until the valve face and valve seat are evenly polished, then clean off all of the compoundNOTE: For best lapping results, lightly tap the valve seat while rotating the valve back and forth between your hands Apply
a fine lapping compound to the valve face and repeat the above steps