Lawn mowers require minimal maintenance save for the occasional oil change and greasing. The mower blade is often neglected, however, even though it is one of the most important components of the machine. A dull mower blade adversely affects the health of a lawn, by ripping at the grass instead of cutting it, and may cause uneven patches in the lawn, opening it to the danger of infection by fungi. Replace the blade every other season or as needed.
Empty the gas tank and oil crankcase so that fluids do not leak into the carburetor while turned over, recommends the Home Improvement Depot. Disable the spark plug so that the machine does not turn on while working on it.
Turn the mower over so that the carburetor is above the gas tank and oil crankcase to prevent drops from getting in.
Secure the mower blade against a scrap piece of wood placed at the bottom of the mower assembly. The Home Improvement Depot recommends placing the mower on a workbench so that the mower is easier to reach into, preventing cuts.
Unscrew the nut holding the blade in place using a crescent wrench. If the nut is stuck, use a spray lubricant to loosen it. Place the crescent wrench around the nut, and hit it gently using a rubber mallet to get the nut moving. Remove the nut.
Remove the old blade, and replace with the new blade. Place the sharp edge of the blade facing in the same direction as the previous blade. Tighten the nut, and refill the engine with gas and oil before testing.