Gas Walk-Behind Mower: Vibrates too much

When your mower vibrates severely, start by checking whether the blade is damaged, imbalanced or loose. Tighten the blade bolt if it's loose. Replace the blade if it's damaged.

A rough-running engine can also cause severe vibrations so tune up the mower to cure engine vibrations.

If you have a hard time pulling the starter rope and the engine sputters when starting your lawn mower, the flywheel key might be damaged.

gas walk-behind mower

These repairs may help solve your gas walk-behind mower problem

Replace a lawn mower blade

Replace a lawn mower blade

A dull or damaged blade won't cut grass evenly. For safety and for a cleaner cut, replace a mower blade that's chipped, broken or otherwise damaged. If the mower vibrates too much, check the mower blade for damage because a bent or unbalanced blade can cause mower vibrations.

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

When your lawn mower blade is no longer making the cut because it's dull, bent or damaged, follow the steps in this repair guide and video show how to replace the mower blade in about 15 minutes.

Repair difficulty
Time required
 15 minutes or less
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Replace a lawn mower flywheel key

Replace a lawn mower flywheel key

The flywheel key is a small metal rectangle that keeps the crankshaft and flywheel aligned when you tighten the flywheel nut. To protect more expensive components from damage, the flywheel key is designed to shear if the mower blade hits an object like a rock or tree stump hard enough to make the flywheel slip out of alignment with the crankshaft. If the flywheel key gets dented when the blade hits an object, the engine runs rough or vibrates severely. If the flywheel key shears when you hit an object, your lawn mower will stop running and won't start. If you inspect the flywheel key and find it dented or sheared, replace it.

How to replace a lawn mower flywheel key on an OHV engine

If your lawn mower died after hitting a rock or tree stump, the flywheel key might have broken. This repair guide and video show how to replace a lawn mower flywheel key.

Repair difficulty
Time required
 60 minutes or less
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How to replace a lawn mower flywheel key on a flathead engine

If your lawn mower doesn't start after hitting a rock or a stump, the mower flywheel pin might have sheared to protect expensive components. This repair guide shows how to replace a lawn mower flywheel key. This guide is for older mower models that have a flathead engine.

Repair difficulty
Time required
 45 minutes or less
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Tune up a lawn mower

Tune up a lawn mower

Tune up a walk-behind mower when the engine runs rough or won't start. You may need to tune up the engine when it vibrates too much or won't stay running. Regular tune-ups prevent engine wear and improve engine efficiency. A walk-behind mower tune-up includes changing the oil, spark plug and air filter. It could also include sharpening or replacing the blade.

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

If your lawn mower engine runs rough or is hard to start, a new spark plug could be the right fix. This repair guide and video explain how to replace a lawn mower spark plug.

Repair difficulty
Time required
 15 minutes or less
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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: uneven wheel height settings, damaged wheel, dull or damaged cutting blade
Main causes: stale gas, engine needs tune up, bad spark plug, dead battery, bad recoil starter, faulty safety switch, bad ignition coil
Main causes: dirty carburetor, bad spark plug, clogged air filter, engine choke problems, clogged gas cap vent
Main causes: damaged cutting blade, loose cutting blade, damaged flywheel key, engine needs tune up
Main causes: engine needs tune up, dirty or clogged carburetor, damaged flywheel key

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 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
April 1, 2013
By Lyle Weischwill
How to replace a lawn mower wheel

Learn how replace a damaged wheel on a walk-behind lawn mower—it's a quick, easy fix.

Repair difficulty
Time required
 15 minutes or less
April 1, 2013
By Lyle Weischwill
How to replace a lawn mower safety switch

The safety switch stops the engine when you release the lever on the handle. This repair guide explains how to replace it if it's not working correctly.

Repair difficulty
Time required
 30 minutes or less

Articles and videos common to all walk-behind mowers

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

October 1, 2019

Types of walk-behind mower blades video

By Sears PartsDirect staff

Learn about the different kinds of mower blades and how to maintain them.