2005-2008 Honda ATV TRX500FA/FGA Fourtrax, Rubicon Factory Service Manual, Page 79Get this manual
MAINTENANCE Rotate the crankshaft using the recoil starter knob and align the "T" mark on the flywheel with the index mark on the alternator coverMake sure the piston is at TDC (Top Dead Center) on the compression strokeThis position can be obtained by confirming that there is slack in the rocker armIf there is no slack, it is because the piston is moving through the exhaust stroke to TDCRotate the crankshaft one full turn and match up the "T" mark again"T" MARK
INDEX MARK
When checking the clearance, slide the feeler gauge from the center toward the outside
Check the clearance of each valve by inserting feeler gauge between the adjusting screw and valve stem