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How to Change the Spark Plug on a Self-Propelled Mower

Changing your spark plug regularly is essential to maintaining your self-propelled lawn mower. If a spark plug is hampered by debris or worn out with time it won't be able to generate the spark needed to start your engine and can reduce the performance and fuel economy of your lawn mower. Check and clean your spark plugs each year and plan on replacing them when they start showing signs of wear and tear. Checking your spark plug can also let you know if there are other lawn mower repairs to be made based on the buildup on the plug.

As you start this project, make sure you have the correct spark plug. Since plugs often look alike, it's important to check your Engine Operator's Manual to make sure you have the correct spark plug for your lawn mower before beginning repairs. The instructions listed below may change based on your model number.

Note: The engine should be cool before changing spark plugs.


Step 1 - Disconnect the spark plug wire

To ensure safety during any lawn mower repair, it's important to disconnect the wire. When changing the spark plug, you'll need to remove the wire to access the plug. Check the condition of the wire at this point as well.

Step 2 - Remove the old spark plug

Use a spark plug wrench and turn counter-clockwise to remove the old spark plug from the mower.

Step 3 - Change the gap on your spark plug

Check the gap on the new spark plug and use a specialized gap tool or a set of feeler gauges to adjust the gap between the electrodes to the appropriate distance as referenced in your operator's manual.

Step 4 - Install the new spark plug

Be careful not to cross-thread when changing spark plugs. You should be able to thread the spark plug in smoothly by hand for a few turns.

Step 5 - Tighten the spark plug

Use a spark plug wrench to continue tightening until the plug is firmly in place. do NOT over-tighten.

Step 6 - Reconnect the spark plug wire

Once you're done changing the spark plug, check for other lawn mower parts that need repair or replacement. Updating anything that needs maintenance with the help of our lawn mower repair how-to articles. Reconnect the spark plug and you're ready to go.