2004 Official factory service manual for Yamaha YFZ450S ATV Quad., Page 77Get this manual
ADJUSTING THE VALVE CLEARANCE b a
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aTurn the crankshaft counterclockwisebWhen the piston is at the Top Dead Center (TDC) on the compression stroke, align the "I" mark on the A.Cmagneto rotor with the stationary pointer on the A.Cmagneto coverNOTE: In order to be sure that the piston is at the Top Dead Center (TDC) the punch mark on the exhaust camshaft sprocket and the punch mark on the intake camshaft sprocket must align with the cylinder head mating surface, as shown in the illustration The Top Dead Center (TDC) on the compression stroke can be found when the camshaft lobes are turned away from each othercMeasure the valve clearance with thickness gauge 1EX IN