October 18, 2018

How to sharpen a lawn mower blade

By Lyle Weischwill
How to sharpen a mower blade
How to sharpen a mower blade

It’s easy to tell when the blade on your push lawn mower is dull: the tips of the grass blades are tattered and brown. If the dull blade is in good shape otherwise, you can sharpen the mower blade yourself by following these instructions. If the blade is bent, warped or chipped, replace it.

For more mower troubleshooting advice and repair instructions, see our lawn mower repair help section.

Tools you need

  • Torque wrench

  • File

  • Wood block

  • Work gloves

Warning: Maintaining power tools can be hazardous. Use the proper tools and safety equipment noted in this 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 maintenance. Some maintenance should only be performed by a qualified technician.

Step-by-step instructions

  1. If you have a gas-powered mower, disconnect the spark plug wire. Carefully tilt the lawn mower on its side with the fuel tank fill hole facing up.

  2. Put on work gloves to protect your hands from cuts. To immobilize the blade, wedge a wood block between the blade and a solid area of the mower housing. You can also use a blade-removal tool to remove the blade.

  3. Remove the bolt and washer, and inspect the bolt. If the blade bolt is damaged, replace it with a manufacturer-approved bolt, rather than a standard bolt. Blade bolts often are specially designed and heat-treated to prevent failure that could cause injury or damage.

  4. Secure the blade in a vise and sharpen the blade with a file. Follow the existing angle of the cutting edge and file in only one direction.

  5. After sharpening, check that the blade is balanced. Drive a finish nail or casing nail into a wall and hang the blade horizontally, through the center hole. If one end dips, grind more from that end.

  6. Use a torque wrench to reattach the blade, tightening the bolt to the torque specified in your owner’s manual—most blade bolts require around 45 to 55 foot-pounds of torque.

  7. Set the mower upright and reinstall the spark plug.

Symptoms for gas walk-behind mowers

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

Main causes: uneven wheel height settings, damaged wheel, dull or damaged cutting blade
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: engine needs tune up, dirty or clogged carburetor, damaged flywheel key
Main causes: drive control cable failure, worn or broken drive belt, bad transmission, broken drive wheel
Main causes: stale gas, engine needs tune up, bad spark plug, dead battery, bad recoil starter, faulty safety switch, bad ignition coil

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.

March 1, 2016
By Lyle Weischwill
How to replace a lawn mower blade

Check your lawn mower blade regularly and replaced it if it's bent or damaged.

Repair difficulty
Time required
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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.

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Time required
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How to replace a lawn mower flywheel key on a flathead engine

When you hit a hard object with your mower, the flywheel can shear to protect more expensive components. Learn how to replace this tiny but essential part.

Repair difficulty
Time required
 45 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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