March 1, 2016

How to replace a lawn mower blade

By Lyle Weischwill
How to replace a lawn mower blade

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.

Follow these steps to replace the cutting blade in Craftsman, MTD, Troybilt, Toro, Husqvarna, Murray, Snapper and Ariens walk-behind lawn mowers.

Quick links
Tools required
Wrench set
Work gloves
Block of wood
Repair difficulty
Time required
15 minutes or less
Repair difficulty
Time required
15 minutes or less
Replacing the blade on a lawn mower

This video explains how to replace the blade on a walk-behind lawn mower.

Instructions

01.

Disconnect the spark plug wire

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

Disconnect the spark plug.

Disconnect the spark plug.

02.

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.
Remove the blade bolt.

Remove the blade bolt.

03.

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.

Install the new blade.

Install the new blade.

04.

Reconnect the spark plug wire

Push the spark plug wire back onto the spark plug.

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.
Symptoms for gas walk-behind mowers

Choose a symptom to see related walk-behind mower repairs.

Main causes: drive control cable failure, worn or broken drive belt, bad transmission, broken drive wheel
Main causes: damaged cutting blade, loose cutting blade, damaged flywheel key, engine needs tune up
Main causes: dirty carburetor, bad spark plug, clogged air filter, engine choke problems, clogged gas cap vent
Main causes: stale gas, engine needs tune up, bad spark plug, dead battery, bad recoil starter, faulty safety switch, bad ignition coil
Main causes: engine needs tune up, dirty or clogged carburetor, damaged flywheel key
Main causes: uneven wheel height settings, damaged wheel, dull or damaged cutting blade
Repair guides for gas walk-behind mowers

These step-by-step repair guides will help you safely fix what’s broken on your walk-behind lawn mower.

How to replace a lawn mower ignition coil on an OHV engine

Replace the ignition coil if it isn't sending electric current to the spark plug when you pull the recoil starter rope.

Repair difficulty
Time required
 30 minutes or less
How to replace a lawn mower flywheel key on an OHV engine

The flywheel key couples the flywheel to the engine crankshaft. Replace the flywheel key if it's broken.

Repair difficulty
Time required
 60 minutes or less
March 1, 2016
By Lyle Weischwill
How to replace a lawn mower drive cable

The drive cable engages the transmission to spin the drive wheels and move the mower across the grass. Replace the drive cable if it's broken or frozen up inside the sheath.

Repair difficulty
Time required
 60 minutes or less
Articles and videos for gas walk-behind mowers

Use the advice and tips in these articles and videos to get the most out of your walk-behind lawn mower.

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How to tune up a lawn mower video
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See how to tune up your mower once a year to keep it running well.

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6 weeks to a better lawn
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April 1, 2015
How to keep grass clippings from sticking to a mower deck
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Prevent your mower deck from rusting by following our advice for keeping grass clippings from sticking.