Proper maintenance is an important part of keeping a lawn mower working correctly over time. One big part of lawn mower maintenance is ensuring that your blade is in good condition. If the lawn mower blade becomes dull, it can't cut the grass. If it becomes bent or damaged, then it is a potential safety hazard. If you hear rattling from the mower deck while the blade is active or you notice that the grass seems jagged instead of cleanly cut, you likely need to change your lawnmower blade. Whether your lawn mower blade is growing dull or somehow became damaged, it's important that you know the proper way to change it safely.
Prepare the Mower
Drain the gas from your lawn mower. Pull the spark plug wire free from the plug before doing any maintenance on the lawn mower blade. This ensures that the mower can't start while you work on the blade and keeps you from spilling gas during lawn mower maintenance tasks. Once you take care of this part, turn the mower onto its side with the air filter facing up to keep oil from filling the carburetor.
If the mower in question is a riding mower, consult your owner's manual to find out how to remove the deck instead of prepping the mower and turning it over. Once the deck is removed, turn it over and access the lawn mower blades mounted on shafts attached to the deck itself.
Secure the Lawn Mower Blade
Wedge a piece of wood or other hard material between the blade and the mower deck. Attempt to turn the lawn mower blade to ensure that the blade is difficult to move while the wood is in place. This helps to prevent potential injuries while attempting to remove the blade during lawn mower maintenance.
Loosen the Blade
Loosen the bolt holding the lawn mower blade on the drive shaft using a wrench or socket, turning the bolt counterclockwise to do so. Hold the blade with a gloved hand as you loosen the bolt to keep the blade from falling free. Once the bolt is removed, pull the blade off of the shaft.
Inspect the Blade
Look at the blade, checking for cracks or other signs of damage. If the blade is dull but undamaged, you can sharpen the edge using a grinder or other tool. If you see cracks, bends or other damage, though, the blade needs to be replaced completely.
Change the Lawn Mower Blade
Place the new or sharpened blade onto the drive shaft with the cutting edge of the blade facing to the right. Place your wood block back under the blade, then use your wrench or socket to replace the bolt by turning it clockwise. Make sure that the bolt is as tight as possible to ensure that the lawn mower blade doesn't come loose during operation.
Test the Mower
Remove the wood block and turn the mower back onto its wheels. Reconnect the spark plug wire and add gas, priming the engine if necessary. Start the mower and listen for noise from the mower deck, then cut a small amount of grass to inspect if the cut is clean. So long as there aren't any odd noises or jagged cuts, your mower is good to go.