2005-2008 Honda ATV TRX500FA/FGA Fourtrax, Rubicon Factory Service Manual, Page 177Get this manual
CYLINDER HEADVALVECAMSHAFT Using 60 interior cutter, remove 14 of the existing valve seat materialOLD SEAT WIDTH TOOLS: Interior cutter, 34 mm (IN) Interior cutter, 30 mm (EX) Cutter holder, 5.5 mm 07780-0014700 07780-0014000 07781-0010101
or equivalent commercially available in U.S.A
Using 45 seat cutter, cut the seat to the proper widthSEAT WIDTH VALVE SEAT WIDTH:1.0-1.1 mm (0.039-0.043 in) Make sure that all pitting and irregularities are removed
Excessive lapping pressure may deform or damage the seat