Step 1: Disconnect the spark plug.
First, disconnect and move the spark plug wire away from the spark plug. This will eliminate any chance of the mower starting while you are working on the blade.
Disconnect the spark plug.
Step 2: Flip the mower on its side.
Flip the mower on its side, being careful not to spill gas and oil from the engine. You can use a tarp underneath the mower to contain any mess. Flip the mower so that the oil breather tube is on high side of the engine and the oil doesn't leak. The best time to do this is when the gas tank is almost empty.
Flip the mower on its side with the oil breather tube facing up.
Step 3: Brace the mower blade.
Next, clamp or brace a block of wood against the mower blade to prevent the rotary blade from moving as you remove the bolt.
Use a wood block to brace the mower blade.
Step 4: Remove the blade.
Wearing gloves to protect your hands, loosen the bolt with a wrench. Remove the bolt, the washer and the blade.
Remove the bolt, washer and blade.
Step 5: Inspect the blade for damage.
Inspect the blade for damage. If the blade is dull but does not have serious dings or nicks, it's a candidate for sharpening. If the blade is even slightly bent or you discover any sign of metal fatigue, such as a hairline crack, replace the blade with a new one of the same length.
Inspect the blade for metal fatigue or cracks.