April 1, 2013

How to replace a lawn mower ignition coil on a flathead engine

By Lyle Weischwill
How to replace a lawn mower ignition coil on a flathead engine

This DIY lawn mower repair guide shows how to replace the ignition coil on a lawn mower that has a flathead engine. The ignition coil sends the electric current to the spark plug to ignite the fuel in the cylinder. If the ignition coil doesn't send electric current to the spark plug when you pull the starter rope, replace the coil with the manufacturer-approved replacement part.

Use this repair procedure to replace the ignition coil on common Briggs & Stratton flathead engines that power Craftsman, Husqvarna, MTD, Murray, Snapper, Toro, Troybilt, Cub Cadet and Ariens walk-behind lawn mowers.

If your lawn mower is a newer model with an overhead valve (OHV) engine, see our repair guide How to Replace a Lawn Mower Ignition Coil on an OHV Engine.

Quick links
Tools required
Phillips screwdriver
Socket wrench set
Feeler gauge
Work gloves
Repair difficulty
Time required
30 minutes or less
Repair difficulty
Time required
30 minutes or less

Instructions

01.

Disconnect the spark plug wire

Wear work gloves to protect your hands.

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

Disconnect the lawn mower spark plug wire.

Disconnect the lawn mower spark plug wire.

02.

Remove the starter rope from the guide

Remove the starter rope from the rope guide. If the rope won't slip past the guide and the handle, loosen the guide.

Remove the starter rope.

Remove the starter rope.

03.

Remove the engine cover

Remove the screws securing the engine cover to the engine. Slide the rope through the hole in the engine cover. 

Remove the engine cover.

Remove the engine cover.

04.

Remove the fuel tank

Remove the screws that secure the fuel tank to the engine. Lift the tank off, being careful to keep the fuel tank upright so it doesn't not leak.

Remove the fuel tank.

Remove the fuel tank.

05.

Remove the dipstick

Remove the screw that secures the dipstick tube to the housing. Remove the dipstick from the engine and plug the hole with a paper towel to keep debris from falling into the engine. 

Remove the dipstick tube.

Remove the dipstick tube.

06.

Remove the engine blower housing

Remove the bolts securing the blower housing to the engine and remove the housing from the engine. 

Remove the blower housing.

Remove the blower housing.

07.

Remove the ignition coil

Turn the flywheel so the magnet is pointing away from the ignition coil.

Remove the screws from the ignition coil.

Lift the ignition coil up and disconnect the kill wire. 

Remove the screws from the coil.

Remove the screws from the coil.

Lift the ignition coil up.

Lift the ignition coil up.

Remove the kill wire.

Remove the kill wire.

08.

Install the new ignition coil

Connect the kill wire to the new ignition coil.

Place the new ignition coil onto the engine. Install the two bolts leaving them loose. Pull the coil away from the engine.

09.

Set the air gap

While holding the feeler gauge in between the coil and flywheel, allow the magnet to pull the coil against the feeler gauge. Tighten the mounting screws.  

Tip: The correct gap for most engines is 0.010-inch.
Insert the feeler gauge.

Insert the feeler gauge.

Tighten the coil mounting screws.

Tighten the coil mounting screws.

10.

Reassemble the mower

Position the engine blower housing on the engine and bolt it into place.

Remove the paper towel from the dipstick opening, slide the dipstick into the engine and secure it with the screw.

Feed the starter rope handle through the engine cover up to the rope guide.

Reinstall the fuel tank.

Position the engine cover on the engine and screw it into place. 

11.

Reconnect the spark plug wire

Attach the spark plug wire and make sure the mower works properly. 

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
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