Sharpen a Lawn Mower Blade
A dull blade tears grass instead of cutting. Tips turn brown, fuel use goes up, lawn looks worse. Takes 20 min once a season.
Disconnect the spark plug
Pull the rubber boot off the spark plug. Absolutely essential — it prevents the mower from starting if the blade rotates.
Drain gas (optional) and tip the mower
Tip with the carburetor side UP so gas and oil don't flood the air filter. Or drain the gas tank first if unsure.
Mark the blade orientation
Mark the bottom-facing side of the blade with a permanent marker before removing. Blades only cut in one orientation.
Remove the blade
Wedge a block of wood between the blade and the deck to stop rotation. Use a socket wrench to remove the center bolt.
Sharpen at the original angle
Use a mill bastard file or bench grinder. Follow the existing bevel angle (usually ~30°). 10–15 strokes per edge is plenty. Don't go razor-sharp — butter-knife sharp is correct.
Balance the blade
Hang the blade on a nail through the center hole. If it tips to one side, file that side more until it balances. An unbalanced blade will destroy the mower's bearings.
Reinstall correctly
Mount with your mark facing down. Tighten the bolt firmly. Reconnect the spark plug.
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