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Your spark plug is one of many lawn mower components that wears out over time. It’s important you address your spark plug during your yearly lawn mower maintenance. In this article, we’ll explain the how and the why of swapping your mower’s spark plug.

Why change your lawn mower spark plug?

A walk-behind lawn mower parked on recently cut grass.
Walk-behind lawn mower | Andres Siimon via Unsplash

A spark plug includes two electrodes that protrude into the combustion cylinder of an engine. When the engine’s electrical system runs power through the plug, a spark leaps from one electrode to the other. This spark ignites the mixture of fuel and air in the cylinder, creating the explosion that drives the engine.

According to the Champion spark plug company, a worn-out spark plug can cause numerous issues. An engine with worn plugs may misfire or idle roughly. It may be hard to start or cease to start at all. It may even suffer compromised gas mileage, reduced power, and poor acceleration.

Whenever you do your yearly lawn mower maintenance–whether it’s while winterizing in the fall or reactivating your mower in the spring–it is important that you service your spark plug.

How to change your lawn mower’s spark plug

Promo photo of a Champion spark plug against a white background.
Spark plug | Champion

First, locate your lawn mower’s spark plug. You are looking for a metal and ceramic shaft that protrudes from the lower engine block of your lawnmower. It is the diameter of a finger and capped with a thick spark plug wire.

You should pull this wire off the end of the spark plug before servicing your mower anyway. Below the plug’s ceramic insulator, near your engine block, you will find your spark plug has a hexagonal ridge, similar to the head of a bolt. Your spark plug is also threaded like a bolt, that is how it stays in place in the engine block. You will need to fit a deep-well socket or a special spark plug wrench over the plug and twist it free like you would any bolt.

Installing a spark plug is just as easy: insert the threaded, electrode end into the engine. Double-check that the plug’s threads are lined up with the threads in your motor, the plug should turn freely at first. Once the shoulder of the plug is flush with the engine, torque it until it’s held firmly in place. This final tightening shouldn’t take more than 1/8-1/4 of a turn. Finally, press the spark plug wire firmly onto the plug. You should feel it snap into place and stay there.

Can you clean and repair an old spark plug?

Closeup of spark plug electrodes firing, on a black background.
Spark plug firing | Champion

If your lawnmower is running poorly, you can remove and examine your spark plugs ahead of schedule. If the plug electrodes are wet with oil or gas, or scorched, that will tell you something about your engine. You can also clean and re-gap your plugs.

Cleaning your spark plug is as simple as using a soft wire brush to clean scouring and debris off of the plug’s electrodes. Re-gapping your old spark plug is a bit more complicated. Sparking for thousands of combustion cycles actually misshapes a spark plug’s central and outer electrode.

To re-gap your spark plugs you’ll need a re-gapping tool. Check out our extensive lawn mower service schedule or see how to re-gap plugs yourself in the video below:


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