How to Replace a Lawn Mower Blade

 

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This step-by-step lawn mower repair guide explains how to replace a lawn mower blade. Check the lawn mower blade often during mowing season to make sure it's sharp and intact. Replace the blade with a manufacturer-approved replacement part if it's dull, damaged or bent. A dull blade tatters the tips of the grass blades rather than making a clean slice. A damaged or bent blade cuts unevenly and can make the mower vibrate excessively. Consider keeping a spare mower blade on hand, so you can install it right away to replace a dull or damaged blade.

Repair difficulty:
     
Time required:

Less than 15 min.

Parts Required

  • Replacement blade

Tools Required

  • Wrench set
  • Work gloves
  • Block of wood

Before you begin

Let the engine cool. 

Wear gloves to protect your hands. 

Place a large piece of cardboard under the mower to prevent stains on the driveway if the engine leaks fluids.  

Instructions

 Warning: Undertaking repairs to appliances can be hazardous. Use the proper tools and safety equipment noted in the guide and follow all instructions. Do not proceed until you are confident that you understand all of the steps and are capable of completing the repair. Some repairs should only be performed by a qualified technician.

How to Replace the Blade on a Lawn Mower

Step 1: Disconnect the spark plug wire

Disconnect the spark wire so there's no chance that the mower could accidentally start.

Step 2: Remove the blade

Remove the fuel tank cap.

Place a plastic bag over the fuel tank opening and reinstall the fuel tank cap to prevent gasoline from leaking out through the fuel tank cap vent.

Tilt the mower back to lift the front wheels then secure the mower handle to your worktable to hold the mower steady.

Wedge a block of wood between the mower blade and the deck to keep the blade from turning when you loosen the blade bolt.

Loosen and unthread the blade bolt while holding the cutting blade to keep the blade from falling.

Pull the blade, blade support and blade bolt off the crankshaft.

 Tip: If you have the mower on the ground instead of a worktable, tilt the lawn mower on its side with the air filter up to access the mower blade.

Step 3: Install the new blade

Position the new blade, blade support and blade bolt on the crankshaft and hand-tighten the blade bolt into the crankshaft.

Wedge a block of wood between the mower blade and the deck to keep the blade from turning when you tighten the blade bolt.

Tighten the blade bolt to 500 in.-lbs. using a torque wrench.

Remove the wood block.

Release the mower handle from the worktable and lower the mower to the upright position.

Remove the plastic bag from the fuel tank.

Step 4: Reconnect the spark plug wire

Push the spark plug wire back onto the spark plug.