2006 Honda TRX680 Rincon Factory Service Manual, Page 88Get this manual
MAINTENANCE Remove the four bolts, intake and exhaust valve adjusting hole capsVALVE ADJUSTING HOLE CAP
Rotate the crankshaft using the recoil starter knob and align the "T" mark on the flywheel with the index mark on the rear crankcase 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