How To Change A Spark Plug In A Lawnmower

Upgraded Home Team
by Upgraded Home Team

Although lawnmowers don’t seem too complicated, they have many intricate pieces and moving parts. In many ways, your lawnmower’s engine is very similar to the one in your car. Various components can wear down and fail, particularly if you haven’t paid much attention to them over the years. The spark plug is one of the most crucial elements in the motor, and if it fails, you will have to replace it.

To change a spark plug in a lawnmower, you will have to disconnect the ignition coil, twist the old plug out, and put the new one in. Once the new spark plug is secure, you can reconnect the ignition and restart the mower to ensure that it’s working correctly.

Fortunately, most lawnmowers have similar engine types, so this process should be relatively identical regardless of your make and model. We will dive into the intricate details so that you can become a pro at changing a spark plug.

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What You’ll Need to Change a Spark Plug in a Lawnmower

  • Screwdriver
  • Spark Plug Socket (this is a special tool to remove old plugs)
  • Socket Wrench
  • Feeler Gauge
  • Spray Cleaner
  • Wire Brush
  • Knife
  • New Spark Plug

Step-by-Step Guide to Changing a Spark Plug in a Lawnmower

Step One: Position the Mower

If you’re working on a push lawnmower, we recommend placing it on a workbench or table. This will make it much easier to do the job since you won’t have to stoop down the whole time. If the spark plug is faulty, you likely won’t be able to turn the machine on. However, if the mower has been running for a while, be sure to let it cool down before starting.

Step Two: Disconnect the Ignition Cable

Whenever you are working on your lawnmower’s engine, it’s always a smart idea to disconnect the spark plug. Doing this will ensure that the mower doesn’t start by accident, causing damage and injury. Knowing where this cable is and how to disconnect it will be handy for virtually all lawnmower repair jobs.

Once the cable is detached, you will want to inspect it. Sometimes, this coil can wear down and rust, which means you have to change it ASAP. Since you’re already replacing the spark plug, it’s a good idea to perform other small repairs as necessary.

Step Three: Remove the Old Spark Plug

Attach the specialized socket to your wrench. Fit it around the top of the plug and twist to the left to get it out. You shouldn’t have to twist too hard – if it’s stuck, you will want to get some penetrating oil or WD-40 to loosen the plug.

You may think that you can use any socket that fits over the plug. However, this is a mistake. Spark plug sockets are designed to avoid damaging the component. If you used a regular socket, you could break the spark plug, making it far more difficult to take out. It is a bit like breaking a light bulb while it is still inside the fixture.

Step Four: Inspect the Old Spark Plug

In some cases, the problem isn’t the piece itself but a buildup of dirt and grime. If that is the case, you can simply clean the plug and reuse it. Here is where the wire brush, spray cleaner, and the knife will come in handy. However, if there are any burned electrodes or cracked ceramic, no amount of cleaning will fix it. Instead, you’ll have to install a new component.

Step Five: Adjust the Gap on the New Spark Plug

If you are replacing the old plug, you can skip this step. Otherwise, you will have to use a feeler gauge to ensure that your new plug is suitable for the engine. If you don’t do this, the plug won’t fire correctly, leading to motor failure or excessive wear and tear.

Because spark plugs are intricate pieces, you have to use a specialized tool to get the right gap. The gap is the space between the curved and straight electrodes on the plug.

Fortunately, if you purchased the correct plug for your lawnmower, you shouldn’t have to adjust the gap too much. You can simply measure the space on the old plug and compare it to the new one. Depending on the type of tool you use, there are different ways to widen or shorten the gap. Follow the specific instructions for your tool so that you don’t damage the electrodes.

Step Six: Install the New Spark Plug

Place the plug into the socket and turn to the right (clockwise). Once it catches, use the socket to tighten it. You want to avoid over-tightening, as you can damage the internal components. In most cases, a quarter turn should suffice.

To test it, try removing the plug. If it comes out too easily, the piece is a little loose. If you have to struggle to move the socket, you’ve tightened it too much.

Step Seven: Reconnect the Ignition Coil

Now that the new plug is in place, you can reinstall the ignition cable.

Step Eight: Test the Mower

Fortunately, you don’t have to go out and mow the lawn to make sure that you did everything correctly. All you need to do is start the mower and let it run for a while. If it has no problems, your installation went smoothly. If it doesn’t start at all, it could be that the gap is incorrect or that the plug is faulty. Start over and see if you can identify the problem.

However, there are multiple reasons for a non-starting mower, so be sure to check out other parts of your engine to see if they are causing the issue.

Tips and Tricks for Changing a Spark Plug

On the scale of difficulty, changing a lawnmower spark plug is relatively easy. However, you can follow these tips to make it an even smoother process.

  • Wear Gloves – Chances are that your mower’s engine is dirty, so wearing gloves can keep your hands clean. Also, there might be some pointy components sticking out, so you can avoid any injury as well.
  • Clean the Motor – If everything is caked in a layer of dirt and grime, take this opportunity to clean the engine. Doing this will extend the life of your machine.
  • Do Your Homework – Spark plugs are not universal, so you need to be sure that you purchase the right one for your make and model. If you’re unsure or the serial number is worn off, take the old plug to a repair shop to get an identical replacement.
  • Use the Right Tools – We’ve mentioned that using incorrect tools for this job can lead to a damaged or faulty plug, so be sure to buy or borrow the items you need. It’s far better to do that than it is to potentially damage your engine.

Signs That the Spark Plug is Faulty

Because this component is integral to your lawnmower’s performance, it is crucial to have a working spark plug. Over time, this piece will wear down, so you will have to change it eventually. Here are some warning signs that the plug is ready to go.

  • Mower Doesn’t Start – This element controls the ignition process, so if your mower doesn’t start at all, the plug could be to blame.
  • Stalls After Starting – The plug also controls the mixture of air and gasoline into the engine, so if it’s not working correctly, it could flood the motor and make it stall out.
  • Rough Idling – If you notice that the mower is sounding rougher or shaking more while you’re not moving, it could indicate a problem with the spark plug.
  • Increased Fuel Consumption – If the plug is faulty, it could be allowing too much gas into the engine. So, if you notice that you have to fill the tank more frequently, it may be time to change this component.

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Related Questions

What if I have a riding lawnmower?

Changing the spark plug on a riding lawnmower should be relatively similar to working on a push model. Be sure to check your owner’s manual for specific instructions and find the plug’s exact location. Depending on where the motor is, you will have to remove some components to get inside.

How can I maintain my spark plugs?

In most cases, the spark plug is a low-maintenance piece. However, if you’re concerned about having to replace it too early, the best thing to do is clean it regularly. We recommend once per season. Also, it helps to remove the plug when putting the mower away for winter.

Upgraded Home Team
Upgraded Home Team

We are a team of passionate homeowners, home improvement pros, and DIY enthusiasts who enjoy sharing home improvement, housekeeping, decorating, and more with other homeowners! Whether you're looking for a step-by-step guide on fixing an appliance or the cost of installing a fence, we've here to help.

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