If your lawn mower blades look like they've been mowing rocks instead of grass, contemplate the simple fact that dull blades damage grass. Dull mower blades tear grass, rip it, or shred it. This is bad news for your lawn. Torn grass is susceptible to many problems like disease, insects, and heat stress. Damaged grass also takes more water for growth and survival. Most lawn owners prefer to avoid this like the plague.
If your lawn mower blade is in bad shape, now would be a great time to replace it. This will require you removing the current blade and installing a new lawn mower blade. Hopefully, you have a spare in your tool shed, but if not you can pick one up at your local garden store.
Another compelling fact in favor of getting rid of that nasty old blade is that gas-powered mowers with sharp blades use roughly 20-percent less fuel than mowers with dull blades according to a study done at the University of Nebraska.
As always, make sure your spark plug is disconnected before working on your mower. Tilt your mower sideways and wedge a wooden block under the deck to keep the blade from moving while you remove it. An even better method is to use a Blade Buster(pictured left) to lock the blade down. It is a good idea to wear gloves because of sharp nics and burs on the old blade. The new blade will be sharp also. Remove the bolt holding the old blade and pull it off your mower.
Fasten the new blade using original washers and bolt. Tighten the bolt that holds the blade with a torque wrench set at 30 pounds. Tighten the bolt with one click and no more. This will prevent your torque wrench from eventually wearing out. Always check to make sure the bolt is tight on the blade before using your mower to prevent any accidents.