Regular maintenance of a lawn mower is essential. Not only does it reduce wear and tear to the engine and other moving components, it keeps the lawn cut evenly. Repairing the mower blades on a regular basis by sharpening them will prevent the grass from looking uneven when cut. Shredded or brown tips of grass, says Colorado State University, indicates a mower blade that needs sharpening. When taking off the blade, inspect it for large dents. If the blade has several large dents or missing pieces of metal, replace it with a new blade.
Remove the spark plug connection from the engine and tie it back to prevent the mower from starting while working on it, Reader's Digest website recommends.
Turn the mower on its side with the air filter above the carburetor to prevent oil and gasoline from leaking into it.
Block the mower blade by securing it against a wood block and mark a small section of the blade with spray paint, so you can determine which side is the top.
Remove the center bolt using a ratchet and take off the blade.
Sharpen dull areas of the blade by running a mill bastard file along the topside of the cutting edge, running the file along the cutting edge at the same angle as the original cutting edge. Use sharp parts of the blade as a guide. Run the blade along the blade until it is butter knife sharp, recommends Reader's Digest, as keeping the blade too sharp will cause the blade to dull more quickly.
Pound a nail into the wall and put the blade onto the nail, balancing it on the middle to test whether the weight is balanced. Remove metal from the heavy side until the blade is balanced and put the blade back onto the mower.