Skip to content

How to change a spark plug on a lawn mower

An MTD Lawn Mower.

You’re pretty good with the do-it-yourself stuff in the garage, but do you know how to change a spark plug on a lawn mower? If not, then look no further.

Lawnmower spark plugs have a ballpark life of about 50 hours, so if you mow the lawn for about half an hour every week, you’re probably going to replace the spark plug every two years. Luckily, the job is an easy one.

Locate Your Manual

As with most jobs that involve changing out components, there are some specifics that vary from brand to brand and model to model, so be sure to consult your owner’s manual. If you don’t have it, you’ll probably be able to find the manual online. When you do, bookmark it for next time.

Get Your Tools

In most cases, you’ll really only need two tools for this job: a spark plug gauge and a spark plug wrench.

All plugs will have a hex ring on them, usually in one of two sizes: 5/8 inch and 13/16 inch. Accordingly, there are three types of spark plug wrenches: one for each of the two sizes and one that can handle both. If your lawn mower uses a different size from what your car, truck or SUV uses, buying the wrench that can handle both might be the best way to go.

Locate the Spark PlugHow to change the spark plug on a lawnmower

The owner’s manual will tell you where the spark plug is. Depending on the model and style of your mower, it may not be immediately visible, and you may need to remove a cover or cowling to access it.

The manual will also specify what type of spark plug you’ll need in terms of size and heat range. You need to make sure the new plug is compatible with your lawnmower, so check the specifics before you buy a new plug. If you do not have the manual, you’ll either have to look up your make and model online or extract the plug, check it for markings and buy an identical one.

Remove the Plug

When you have the spark plug gauge, spark plug wrench and a new spark plug, it’s pretty simple from there. First, remove any cover that might be obstructing your access. While you should always defer to your manual, you’ll likely have to disconnect the spark plug wire that leads to the engine next. Disconnecting this wire is also a good safety step to take before you work on your mower, as it ensures that there can be no accidental ignition.

Put the socket of your wrench over the hex ring of the old plug and twist counter-clockwise until the plug comes out.

Match the Gap

Every plug has a gap between its electrodes at the tip. When electricity flows across this gap, the spark is created, but the gap of your new plug may need to be adjusted. Use your spark plug gauge to measure the width of the gap on the old plug. You should be able to bend the new plug’s electrode gently by hand to match the old one and keep your mower operating as it always did.

Install the New Plug

Putting in the new plug is just the reverse of removing the old one. Use your wrench to secure it to the mower, and be careful not to over-tighten it. There may be recommendations about how tight to go in your manual. From there, reconnect the wire, and you’re ready to run.

Remember, spark plugs should be changed every two years, so they’re a key part to check if your mower seems to be struggling after a few seasons without maintenance. Even if there’s no problem, doing so on a consistent basis will pay off in reliable starts and more consistent fuel economy.

Check out all the spark plugs and accessories available on NAPA Online, or trust one of our 17,000 NAPA AutoCare locations for routine maintenance and repairs. For more information on how to change a spark plug on a lawn mower, chat with a knowledgeable expert at your local NAPA AUTO PARTS store.

Photos courtesy of Wikimedia Commons.

Mike Hagerty View All

Mike Hagerty is an automotive journalist whose work has been featured on radio, TV, in print and online since 1997. He's the Publisher and Editor of, and contributes car reviews to the Los Altos Town Crier and Previous outlets have included KFBK and in Sacramento, California, the ABC television affiliates and Hearst-Argyle and Emmis radio stations in Phoenix, Arizona; AAA magazines for Arizona, Oklahoma, Northwest Ohio, South Dakota and the Mountain West and

Leave a Reply

Your email address will not be published. Required fields are marked *