How to Replace a Lawn Mower Ignition Coil on a Flathead Engine

 

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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.

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.

Repair difficulty:
     
Time required:

Less than 30 min.

Parts Required

  • Ignition coil

For manuals, repair guides, and specific part recommendations, enter your model number.

Tools Required

  • Philips screwdriver
  • Socket wrench set
  • Feeler gauge
  • Work gloves

Before you begin

Let the engine cool. Wear gloves to protect your hands.

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.

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 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.

Step 3: Remove the engine cover

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

Step 4: 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.

Step 5: 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. 

Step 6: Remove the engine blower housing

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

Step 7: 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. 

Step 8: 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.  

Step 9: 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 guage. Tighten the mounting screws.  

 Tip: The correct gap for most engines is 0.010"

Step 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. 

Step 11: Reconnect the spark plug wire

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