How to Remove a Spark Plug on a Lawn Mower?

The satisfying hum of a freshly tuned lawnmower is a sound that brings joy to any homeowner’s heart. But what happens when that familiar hum turns into a sputtering cough? A fouled or worn-out spark plug can be the culprit, leaving your lawnmower struggling to start and maintain a steady performance. Fortunately, replacing a spark plug is a relatively straightforward task that most homeowners can tackle with a few basic tools and a little know-how. This guide will walk you through the steps of removing a spark plug on your lawnmower, ensuring you can get your mower back in tip-top shape and tackle that overgrown patch of grass with ease.

A Quick Overview

Removing a spark plug on a lawnmower is a simple process that requires basic tools like a spark plug socket, wrench, and gloves. The procedure involves disconnecting the spark plug wire, using the spark plug socket to loosen and remove the spark plug, and then inspecting the old plug before installing the new one.

Safety First: Essential Precautions

Before diving into the task, it’s crucial to prioritize safety:

  • Always disconnect the spark plug wire: This prevents accidental ignition while working on the engine.
  • Wear appropriate protective gear: Gloves protect your hands, and safety glasses shield your eyes from any potential debris.
  • Work in a well-ventilated area: Engine fumes can be harmful, so ensure proper airflow.
  • Keep children and pets away: The area around the lawnmower should be clear to prevent any accidental contact with the tools or moving parts.

Gathering Your Tools

To remove a spark plug on a lawnmower, you’ll need these essential tools:

  • Spark plug socket: This specialized socket fits the hex shape of the spark plug. You can find them in various sizes, so ensure you get the correct one for your mower.
  • Wrench: This will be used to tighten or loosen the spark plug socket.
  • Gloves: Protects your hands from dirt, grease, and potential burns.
  • Safety glasses: Protects your eyes from flying debris.
  • New spark plug: Ensure you purchase a spark plug that matches your lawnmower’s specifications.

Locating the Spark Plug

The spark plug is typically located on the top of the engine, near the cylinder head.

Identifying the Spark Plug Wire

The spark plug wire is usually a thick, insulated cable connected to the top of the spark plug. It may be colored or have markings to help distinguish it from other wires.

Disconnecting the Spark Plug Wire

  1. Locate the spark plug wire: Identify the wire connected to the spark plug.
  2. Pull the wire straight up: Gently pull the wire upwards, removing it from the spark plug terminal.
  3. Keep the wire away from the engine: Place the wire away from any hot engine components to prevent accidental contact.

Removing the Spark Plug

  1. Position the spark plug socket: Align the socket with the spark plug and gently press it onto the plug.
  2. Use the wrench to loosen the spark plug: Turn the socket counterclockwise to loosen the spark plug. You may need to apply some force, but avoid over-tightening.
  3. Remove the spark plug: Once the spark plug is loose enough, gently pull it out of the cylinder head.

Inspecting the Old Spark Plug

Once the old spark plug is removed, inspect it carefully for any signs of wear or damage:

Inspecting the Electrode

  • Electrode wear: The electrode should be smooth and rounded. Excessive wear or a sharp edge can indicate a worn-out plug.
  • Electrode gap: The gap between the electrode and the center electrode should be within the manufacturer’s specifications. You can check this using a feeler gauge.
  • Deposits: The electrode and insulator may have carbon deposits. These can affect performance and should be cleaned or replaced.

Inspecting the Insulator

  • Cracks or damage: The insulator should be free of any cracks or damage.
  • Soot build-up: The insulator may have soot buildup, which can hinder spark performance.

Installing the New Spark Plug

  1. Clean the cylinder head: Use a wire brush or a clean cloth to remove any debris from the cylinder head threads.
  2. Install the new spark plug: Gently thread the new spark plug into the cylinder head. Make sure it’s seated properly.
  3. Tighten the spark plug: Use the spark plug socket and wrench to tighten the spark plug to the manufacturer’s specifications. Overtightening can damage the threads, so avoid excessive force.
  4. Reconnect the spark plug wire: Gently push the wire back onto the spark plug terminal, ensuring a secure connection.

Starting the Engine

After installing the new spark plug, you can start the engine to test its performance. If the engine starts smoothly and runs well, you’ve successfully replaced the spark plug.

Troubleshooting Common Issues

The Engine Won’t Start

If the engine fails to start after replacing the spark plug, check the following:

  • Spark plug wire connection: Ensure the spark plug wire is securely connected to both the spark plug and the ignition coil.
  • Fuel supply: Verify that the fuel tank has fuel and the fuel lines are clear.
  • Spark plug gap: Ensure the new spark plug has the correct gap setting.

The Engine Starts But Runs Poorly

If the engine starts but runs poorly, consider the following:

  • Spark plug gap: Double-check the spark plug gap to ensure it’s within the manufacturer’s specifications.
  • Fouled spark plug: The new spark plug may have become fouled during installation. Check for excessive carbon buildup on the electrode and insulator.

Maintaining Your Lawn Mower

Replacing the spark plug is just one aspect of keeping your lawnmower running smoothly. Regular maintenance is key to maximizing performance and extending your mower’s lifespan:

  • Change the oil regularly: Follow the manufacturer’s recommended oil change intervals.
  • Clean the air filter: A dirty air filter restricts airflow to the engine, reducing performance.
  • Inspect the spark plug: Check the spark plug condition at least once a season.
  • Sharpen the blade: A dull blade can damage your lawn and strain the engine.


Replacing a spark plug is a simple and essential maintenance task that can significantly improve your lawnmower’s performance and longevity. By following the steps outlined in this guide, you can confidently tackle this task yourself and ensure your mower is ready to conquer any overgrown patch of grass. Remember to always prioritize safety, gather the necessary tools, and follow the manufacturer’s instructions for your specific lawnmower model. Happy mowing!


Q1: What tools do I need to remove a spark plug?

A: You’ll need a few basic tools: a spark plug socket, a wrench that fits the socket, and a gap gauge. A spark plug socket is a specialized socket with a rubber insert that grips the spark plug without damaging it. The wrench is used to loosen and tighten the spark plug, and the gap gauge is used to measure the distance between the spark plug electrodes. Make sure to choose the correct size socket for your lawnmower’s spark plug.

Q2: How do I disconnect the spark plug wire?

A: Before you remove the spark plug, you need to disconnect the spark plug wire. This is important for safety, as it prevents the engine from sparking while you’re working on it. To disconnect the wire, gently pull on the boot, which is the rubber part of the wire that connects to the spark plug. It may be helpful to use a spark plug wire puller, which is a tool designed to safely remove the boot.

Q3: What do I do if the spark plug is stuck?

A: If the spark plug is stuck, you can try loosening it with a wrench. If it’s still stuck, you can try using a spark plug socket wrench with a breaker bar. This will give you more leverage to loosen the spark plug. Be careful not to strip the spark plug threads when using a breaker bar. If the spark plug is extremely stuck, you may need to use penetrating oil and allow it to soak in before trying to loosen it again.

Q4: How do I clean the spark plug?

A: You can clean the spark plug with a wire brush or a piece of sandpaper. You want to clean the electrodes of the spark plug so that it can spark properly. If you find that the spark plug is heavily corroded or worn, you may need to replace it.

Q5: How do I check the spark plug gap?

A: To check the spark plug gap, you’ll need a gap gauge. The gap is the distance between the two electrodes on the spark plug. You can adjust the gap by bending the electrode that is attached to the spark plug’s body. The correct gap is usually specified in your lawnmower’s owner’s manual.

Q6: How do I install the new spark plug?

A: Once the new spark plug is installed, tighten it with a wrench. You want to tighten it until it is snug, but do not overtighten it. The recommended torque for tightening a spark plug is usually listed in your lawnmower’s owner’s manual. Make sure the spark plug wire is securely connected to the new spark plug.

Q7: What should I do with the old spark plug?

A: It’s best to dispose of the old spark plug properly, as it contains hazardous materials. You can take it to a recycling center or a local mechanic, who will dispose of it safely. You can also keep the old spark plug in case you need to replace it again in the future.

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