When your lawn mower begins cutting grass unevenly, or the mower is shaking as you use it, the blade could be bent, dented or dull. A regular part of lawn mower maintenance is the removal and replacement of bad mower blades. Removing and replacing a lawn mower blade is not overly technical, so most who can use a wrench will be able to do this simple repair. Always make sure you use the correct part for your machine by noting the model number and using a reputable parts dealer.
Removing and Replacing the Blade
Unplug the spark plug from your lawn mower to prevent the mower from starting while working on it. Put on your safety glasses and gloves before you begin working.
Drain the mower of gasoline and oil before tipping the mower on its side, as these liquids will get into the carburetor, rendering it useless. Use a gas siphon to remove the gas from the tank, and remove the oil plug from the crankcase.
Secure the blade of the lawn mower against the block of wood to prevent the blade from moving while you are taking off the bolt. Secure one end of your piece of wood into some soft earth, and force the blade against it.
Adjust your wrench against the bolt of the mower blade, and turn left to loosen it. Pound the wrench with a rubber mallet to remove it if refuses to budge. Forcing your weight against the wrench could cause it to pop off the bolt, making you slam your hand into the bottom of the mower.
Remove the blade from the bottom of the mower. Take the old blade to a hardware store to find a replacement.
Put the new blade on to the mower, making sure all the washers are in place and that the sharp end of the blade is facing in the correct direction. Make sure the blade is tightly secured, turning it a few times by hand to ensure that it is not loose.