2007-2009 Honda TRX300EX TRX300X service manual, Page 50Get this manual
MAINTENANCE Rotate the crankshaft counterclockwise and align the "T" mark on the flywheel with the index notch in the left crankcase coverMake sure the piston is at TDC (Top Dead Center) of the compression stroke by moving the rocker armsIf the exhaust rocker arm is tight, turn the crankshaft counterclockwise one full turn (360) and realign the "T" mark with the index notch
Check the clearance of each valve by inserting the feeler gauge between the adjusting screw and valve stemVALVE CLEARANCE: IN: 0.10 mm (0.004 in) EX: 0.10 mm (0.004 in)
Adjust by loosening the lock nut and turning the adjusting screw until there is slight drag on the feeler gaugeTOOLS: Valve adjusting wrench, 10 12 mm Valve adjusting wrench 07708-0030200 or equivalent commercially available in U.S.A07708-030400 or 07908-KE90200 (U.S.Aonly)