2004 Official factory service manual for Yamaha YFZ450S ATV Quad., Page 111Get this manual
ADJUSTING THE DRIVE CHAIN SLACK
ADJUSTING THE DRIVE CHAIN SLACK NOTE: Measure the drive chain slack halfway between the drive axle and the rear axleCAUTION: drive chain that is too tight will overload the engine and other vital parts, and one that is too loose can skip and damage the swingarm or cause an accidentTherefore, keep the drive chain slack within the specified limits1Elevate the rear wheels by placing the suitable stand under the frame
2Measure: drive chain slack Out of specification Adjust