2003 2005 YFM45FAR, YFM450FAR Kodiak OEM Service Manual, Page 154Get this manual
CAMSHAFT, ROCKER ARMS AND VALVES
Measurement steps: Apply Mechanic's blueing dye (Dykem) to the valve faceG Install the valve into the cylinder headG Press the valve through the valve guide and onto the valve seat to make clear patternG Measure the valve seat widthWhere the valve seat and valve face made contact, blueing will have been removedG If the valve seat is too wide, too narrow, or the seat is not centered, the valve seat must be refaced