If you ever have to replace or remove an old mower blade for sharpening, it’s important to do it safely. The big challenge in this job is removing the old blade. Start by disconnecting the spark plug from the motor for safety. You want to remove any chance that the blade could spin and cause the motor to start.
Then turn the mower on its side. Ideally, the gas tank should be empty. And make sure you tip it so the carburetor is facing up to prevent fuel from spilling out.
Now you can remove the blade. It’s held in place with a bolt in the center. The problem is that when you try to loosen the bolt, the blade just turns. To prevent that, clamp a block of wood under the mower deck to jam the blade and stop it from turning (Photo, above). Now remove the bolt. They can be stubborn, so you may need a long wrench or a breaker bar.
Once you get the blade off, take it to the hardware store or the store where you bought the mower. Even if the blade is damaged, they may be able to sharpen it, which is cheaper than buying a new blade. If the blade is too beat-up, use it to get the correct size replacement.
Then you can reinstall the blade. You’ll need to rotate the blade so it again rests against the block of wood to prevent spinning. Just be sure to get it oriented correctly. It’s usually easy to tell, but not on all blades. If you place the blade upside down, the dull edges will be leading as it spins, and it will do a very poor job of cutting the grass.