A sharp, balanced mower blade cuts grass cleanly and reduces the tearing that leaves lawns ragged and brown. Blade work begins with disabling the mower completely; never reach beneath a mower deck with the blade still connected.
Make the mower safe
For a gas mower, disconnect the spark-plug wire and secure it away from the plug. For an electric or battery mower, remove the battery and key. Tilt the mower according to its manual to protect the air filter and carburetor, or use a proper service stand.
Remove and mark the blade
Wear gloves and mark the upward-facing side before loosening the retaining bolt. Use a block of wood to prevent rotation, not your hand. Inspect the blade for deep bends, cracks, missing metal, or excessive thinning; replace it when damage is structural.
Restore the cutting edge
Clamp the blade securely and follow the original bevel with a file or grinder. Remove only enough metal to restore a consistent edge, keeping both ends similar. Avoid overheating the steel, which can weaken it, and do not turn the blade into a razor edge.
Balance before reinstalling
Rest the blade on a nail or balancing tool through its center hole. If one side drops, remove a small amount from that side and test again. Reinstall with the marked side up, tighten to the manufacturer’s specification, reconnect the safety components, and run the mower briefly while listening for vibration.
Unusual vibration, a loose blade, or a damaged crankshaft calls for professional service. Keep a spare blade available so mowing does not become a rushed repair job.