2002 Yamaha YFM660 Grizzly factory service and repair manual, Page 168Get this manual
VALVES AND VALVE SPRINGS
REMOVING THE VALVE AND VALVE SPRING 1.Check: Valve sealing Leakage at the valve seat Inspect the valve face, valve seat and valve seat widthRefer to "CHECKING THE VALVE AND VALVE SPRING" Checking steps: Pour clean solvent into the intake and exhaust portsCheck that the valve seals properlyThere should be no leakage at the valve seat 2