2004 Official factory service manual for Yamaha YFZ450S ATV Quad., Page 191Get this manual
BALANCER
REMOVING THE BALANCER DRIVE GEAR AND BALANCER DRIVEN GEAR 1Straighten the lock washer tab2Loosen: primary drive gear nut balancer driven gear nut NOTE: Place an aluminum plate between the teeth of the balancer drive gear and driven gear 43Remove: balancer drive gear balancer driven gear