A study conducted by the University of Nebraska found that gas-powered riding mowers operated with sharp blades use 20 less fuel than those with dull blades. For this reason alone, changing and sharpening your riding mower blade is important. Keeping the blades sharp enhances the appearance of your lawn with a pristine cut and strengthens the grass blades. Mowing with a dull blade will tear at the grass rather than cut, leaving damage in its wake.
Park the mower on a flat surface and engage the parking brake. Place a block of wood under the deck on the rear side and in the front. Lower the deck to its lowest setting, allowing it to sit on the wood blocks. Remove the drive belt from the pulley, stretching it over the edge until it becomes unattached. Detach the front- and rear-deck fasteners according to the owner's manual. Remove the wood blocks from under the deck and slide the deck away from the underside of the tractor.
Turn the deck over with the blades facing up. Secure the blade with a wood block so that it cannot turn. Remove the blade, turning the nut in the center of the blade with a wrench to loosen it. Remove the nut and slide the blade off the shaft. Clean debris from the bottom of the mower deck.
Position the new or sharpened blade over the spindle with the curved end pointing toward the mower deck. Screw the nut over the shaft, tightening by hand. Secure the blade with a wood block and tighten the nut further, using the wrench.
Slide the deck under the tractor. Raise it with wooden blocks placed under the front and rear of the deck. Lower the deck control to the lowest setting, and reattach the drive belt to the belt pulley. Pull the belt tightly around the pulley. Reattach any fasteners that were removed. Raise the mower deck and remove the wooden blocks.