How to Remove and Sharpen a Lawn Mower Blade

Disconnect the spark plug wire. Tip the mower on its side with the air filter facing UP to prevent oil from flooding the filter.

Wedge a block of wood between the blade and deck to prevent the blade from spinning while you loosen the bolt.

Remove the center bolt (usually 15/16" or 5/8") by turning counterclockwise. This bolt can be very tight — a breaker bar helps.

Note which side of the blade faces down (toward the ground). Most blades have a stamp or label on the top side. Installing upside-down means no cutting.

Secure the blade in a vise. Inspect for cracks, bends, or severe damage. If bent or cracked, replace — don't sharpen.

Using a mill file or angle grinder, sharpen the cutting edge following the existing bevel angle (usually about 30 degrees). File in one direction — from the inside out. Remove the same amount of material from each end.

Check the balance by hanging the blade on a nail through the center hole. If one side drops, file a little more from that side. An unbalanced blade causes vibration.

Reinstall the blade with the cutting edge facing the correct direction (stamped side up). Tighten the bolt firmly — 35-50 ft-lbs is typical.

Remove the wood block, set the mower upright, and reconnect the spark plug wire.