Tools

Supplies

Reasons to Change Your Lawn Mower Spark Plug

  • Helps your lawn mower run better/more efficiently.
  • Replace the spark plug approximately every 25 mows.
  • Maintaining power equipment helps it last longer.

Before You Get Started

  • Wear work gloves to prevent blisters during a manual procedure.
  • Wear safety glasses to protect your eyes while working on equipment.
  • If servicing your mower, carefully follow the manufacturer’s suggested safety precautions.

How to Change a Lawn Mower Spark Plug

Step 1 Source the Correct Spark Plug

Determine the model number of your lawn mower and purchase a new spark plug that fits your mower.

a new lawn mower spark plug
Find the correct spark plug for your mower.
PRO TIP
Compare the new spark plug with the old plug to make sure it is the same.

Step 2 Remove the Spark Plug Wire Cap from the Spark Plug

There is a plastic or rubber cap that covers the end of the spark plug. Firmly grasp the cover and pull it off the end of the spark plug.

spark plug cap
Remove the cap from the end of the spark plug.

Step 3 Use a spark plug socket to remove the spark plug.

Spark plugs are typically screwed firmly into the engine block, so you will need a deep-well spark plug socket and a ratchet to remove the spark plug. Common sizes of sockets for lawn mower plugs include 5/8” and 11/16”. Spark plug sockets will usually have a rubber insert inside the socket to grasp the end of the plug.

spark plug socket and ratchet
Use a ratchet and an extension with the spark plug socket.
PRO TIP
You may also need a socket extension to reach the plug if it is recessed inside the mower. Turn the ratchet to the right to loser (counter clockwise) or to the left to tighten.

Step 4 Unscrew the Spark Plug and Compare

Once you have the plug loose, remove it from the mower’s engine. Look for a number on the plug, and compare the new plug to the old plug. Make sure that the bottom of the plug is the same length.

old and new spark plug
Compare the new plug to the old plug.

Step 5 Check the Spark Plug Electrode Gap

Look at the new spark plug and make sure that the new plug has the proper gap between the center electrode. It should be gapped correctly from the factory. You can check the gap with a special spark plug gap tool or a feeler gauge. The center electrode should not touch.

Check the plug gap
Make sure the spark plug gap is in spec.

Step 6 Use the socket to reinstall the spark plug.

Tighten the plug first by hand, being careful not to cross the threads. Once the crush washer on the spark plug touches the engine block, give the plug a quarter turn with the socket to make sure it is firmly seated.

Tighten spark plug with socket
Use the socket to tighten the spark plug.

Step 7 Reinstall the spark plug boot on the spark plug.

Put the spark plug boot over the end of the spark plug and firmly push it into place. You will often hear a “click” once the boot is seated on the plug.

Push on the spark plug boot
Firmly push on the spark plug boot.