2001 Yamaha YFM660 Raptor Factory Service Manual, Page 208Get this manual
VALVES AND VALVE SPRINGS
8.Measure: Valve seat width Out of specification Reface the valve seatValve seat width: Intake: 0.91.1 mm (0.03540.0433 in) Limit: 1.6 mm (0.0630 in) Exhaust: 0.91.1 mm (0.03540.0433 in) Limit: 1.6 mm (0.0630 in)
Measurement steps: Apply Mechanic's blueing dye (Dykem) to the valve faceInstall the valve into the cylinder headPress the valve through the valve guide and onto the valve seat to make clear patternMeasure the valve seat widthWhere the valve seat and valve face made contact, blueing will have been removedIf the valve seat is too wide, too narrow, or the seat is not centered, the valve seat must be refaced