Different types of mower blades are designed to do different jobs. You might have one blade for mulching and another for regular clipping. If; however, your mower blades are not properly sharpened, the blades will be dull and not cut as they should. The blades on your mower should be checked for damages, proper shape and should be sharpened at least once per month.
As we always like to think “safety first,” it is essential that you always wear gloves and eye protection when working with mower blades. Small splinters of metal can cut your hands and worse yet, get caught in your eye. This issue is even more pressing if you use an electric blade sharpener or bench grinder.
The next thing is to remove the spark plug wire. Place a piece of electric tape over the end and add additional tape to secure it to the outer mower casing so that it doesn’t get near the spark plug. This will prevent accidental start-up should you spin the blade around. Even with modern safety measures, such as the handle-grip blade engagement, take this one measure of caution—you might just keep your fingers. You’ll also want to empty the gas tank and turn the mower on its side (gas tank side down) to prevent the oil and gas residue from mixing.
Removing the blade can sometimes be a bummer, especially if you haven’t done so for some time. Go ahead and spray a dab of penetrating oil on the back nut to loosen it up. Wait a few minutes. Next, use either a blade holder or a clamp to hold the blade in place as you loosen the nut. The blade bolt might be a little hard to loosen, but once removed, remember what nuts (and in some cases washers) go where, so that’s it’s not confusing when you want to put the parts back together. Scrape the grass and use an air compressor if necessary.
Sharpening the blade can be done with a file or a mower blade grinder. Check the manufacturers book to see the exact angle you should use to sharpen the blade. If you cannot access the book, don’t fret; just try to keep the same angle as the factory original.
Don’t overly push the blade into the grinder. Take it nice and slow, moving the blade back and form over the grinder. Don’t grind and make it hot as the metal can quickly lose its strength. It should be sharp, without too many nicks and straight. A blade balancer can help you check its balance. They are not 100% necessary, but are highly recommended. You can check it by balancing it on the end of a screwdriver if needed. If your blade has a lot of damage (too many nicks or is uneven or way out of balance) be sure to replace it rather than chance your safety once it’s spinning under the deck.
Now it’s time to reattach the blade. Remounting it shouldn’t take too long if you’ve been careful to check how the blade goes back on the main bolt. Be sure to be careful here too. The spark plug wire should still be separated from the plug. Reattach the bolt(s) and washer(s) carefully. Tighten them a half turn to three-quarter turn past snug. You can check exact pressure ratings in your user manual. They should be tight, but not so tight that when the blade gets hot the bolt and nut mesh.
Now, turn the mower over properly, reattach the spark plug wire and partially fill with gas (a small amount will do in case you have to check the underneath again). Start the mower and make sure the mower doesn’t vibrate (which signifies an imbalanced blade and is dangerous for you and engine life). Additionally, check that the blade doesn’t nick the edge of the mower deck.