2000 Yamaha YFM400FWA(M) Factory Service workshop Manual, Page 135Get this manual
CYLINDER HEAD
NOTE: Be sure the punch mark on the camshaft sprocket is aligned with the match mark on the cylinder head Force
the camshaft clockwise and counterclockwise to remove timing chain slackInsert screwdriver into the timing chain tensioner hole and push the timing chain guide inwardWhile pushing the timing chain guide, be sure that the camshaft sprocket punch mark is aligned with the cylinder head match mark 2If the marks are aligned, tighten the camshaft sprocket boltIf the marks are not aligned, change the meshing position of the camshaft sprocket and timing chain