2002 Yamaha YFM660 Grizzly factory service and repair manual, Page 131Get this manual
ADJUSTING THE REAR SHOCK ABSORBER CHECKING THE TIRE
ADJUSTING THE REAR SHOCK ABSORBER 1.Remove: Rear wheels 2.Adjust: Spring preload Turn the adjuster to increase or decrease the spring preloadNOTE: The spring preload of the rear shock absorber can be adjusted to suit the rider's preference, weight, and the riding conditionsStandard position: Minimum (Soft) position: Maximum (Hard) position: 3.Install: Rear wheels