2004 Official factory service manual for Yamaha YFZ450S ATV Quad., Page 165Get this manual
VALVES AND VALVE SPRINGS
aApply Mechanic's blueing dye (Dykem) to the valve facebInstall the valve into the cylinder headcPress the valve through the valve guide and onto the valve seat to make clear patterndMeasure the valve seat widthWhere the valve seat and valve face made contact, blueing will have been removedeIf the valve seat is too wide, too narrow, or the seat is not centered, the valve seat must be refacedLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLL
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