How to Change a Spark Plug on a Lawn Mower in 5 Easy Steps

How to Change a Spark Plug on a Lawn Mower in 5 Easy Steps


Changing the spark plug on your lawn mower is a crucial maintenance task that enhances both performance and efficiency.

A worn or dirty spark plug can lead to starting difficulties, poor fuel economy, and rough operation.

By learning how to change a spark plug properly, you can ensure that your lawn mower runs smoothly and reliably.

This guide will provide a clear, step-by-step process to replace your lawn mower’s spark plug, highlighting the tools you’ll need and the best practices to follow.

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Step 1: Gather Your Tools

Before you start, make sure you have all the necessary tools and materials:

  • A new spark plug that matches your lawn mower’s specifications.
  • A spark plug socket or wrench.
  • A socket wrench.
  • A gap gauge for adjusting the spark plug gap (if necessary).
  • Use a clean rag or brush to clean the area around the ignition.

Step 2: Locate the Spark Plug

Access the Spark Plug:

First, ensure the lawn mower is off and cool.

Locate the spark plug; it’s typically near the front or side of the engine and connected to a thick rubber hose.

Remove the spark plug wire by gently twisting and pulling the boot away from the spark plug.

Step 3: Remove the Old Spark Plug

Unscrew the Spark Plug:

Attach the spark plug socket to your socket wrench.

Fit the socket over the spark plug and turn counterclockwise until the spark plug is loose.

Remove the spark plug by hand once it’s loose enough.

Step 4: Install the New Spark Plug

Check and Adjust the Gap:

Use the gap gauge to ensure the new spark plug gap matches your mower’s specifications.

Screw in the New Spark Plug:

Hand-tighten the new spark plug to avoid cross-threading.

Once hand-tight, use the wrench to tighten it slightly more, but avoid over-tightening to prevent damage.

Step 5: Reattach the Spark Plug Wire

Secure the Connection:

Reattach the spark plug wire by pushing the boot onto the new spark plug until you feel it click into place.

Ensure the connection is snug to prevent any misfires.


Changing the spark plug is a simple yet vital part of maintaining your lawn mower’s health and operational efficiency.

Regularly replacing the spark plug will help you avoid engine problems and keep your mower running effectively. With this guide, you’re well-equipped to handle this task with confidence.

Step 1: Preparation

Before diving into the task of changing the spark plug on your lawn mower, proper preparation is essential to ensure a safe and effective operation.

This step is crucial in preventing any accidental starts and avoiding contamination of critical engine parts.

Disconnect the Spark Plug Lead

Safety First:

Begin by ensuring the lawn mower is completely turned off and has cooled down. This prevents any burns or other injuries.

Locate the spark plug wire, which is usually attached to the spark plug with a rubber boot. Firmly grasp the boot and gently pull it to disconnect the wire. This is an important safety measure to prevent the lawn mower from accidentally starting while you are working on it.

Clean the Area Around the Spark Plug

Avoid Contamination:

Use a clean brush or rag to clean around the spark plug area thoroughly. This step is vital to prevent dirt, grass, or debris from falling into the combustion chamber once the spark plug is removed.

Ensuring that this area is clean also helps in the easy removal and installation of the spark plug, keeping the surrounding engine parts in good condition.

Ensure a Well-Ventilated Workspace

Proper Ventilation:

Make sure to perform this maintenance in a well-ventilated area, preferably outdoors. This not only provides a safe environment but also prevents the inhalation of any fumes or airborne debris during the cleaning process.

These preparatory steps are fundamental in setting the stage for a smooth and safe spark plug replacement, protecting both you and the mower’s engine.

Taking the time to prepare properly prevents potential problems and ensures that the maintenance goes as smoothly as possible.

Step 2: Removing the Old Spark Plug

Removing the old spark plug is a critical step in the maintenance process, requiring careful handling to avoid damage to the mower’s engine or the spark plug itself.

This step ensures that your lawn mower continues to operate efficiently.

Disconnect the Spark Plug Wire

Safety Check:

Ensure that the mower’s engine is completely cool before you begin. This is crucial to avoid any burns or unintended sparks.

Carefully disconnect the spark plug wire by pulling on the boot, not the cable, to prevent damaging the wire.

Use a Spark Plug Socket

Loosen the Spark Plug:

Attach a spark plug socket to your wrench. Fit the socket over the spark plug and turn it counterclockwise.

Gently loosen the spark plug until you can remove it by hand. It’s important to proceed with care to avoid cross-threading or damaging the spark plug hole.

Clean the Spark Plug Well

Remove Debris:

Once the spark plug is removed, inspect the well where the spark plug was seated. Use a wire brush or a spray-on plug cleaner to clean out any debris, dirt, or buildup.

Cleaning this area prevents debris from entering the combustion chamber when the new spark plug is installed.

Inspect the Old Spark Plug

Assess Condition:

Examine the old spark plug for signs of wear or fouling. Look for any damage or unusual deposits that could indicate engine issues.

This inspection can provide valuable insights into the overall health of your mower’s engine and whether additional maintenance might be needed.

By following these steps, you ensure that the engine is prepared for the installation of a new spark plug, maintaining the mower’s efficiency and reliability.

This careful removal also helps in diagnosing potential engine problems early, based on the condition of the old spark plug.

Step 3: Inspecting and Adjusting the Spark Plug Gap

Properly setting the spark plug gap is crucial for optimal engine performance.

The gap between the electrodes affects how the spark ignites the fuel in your lawn mower’s engine.

This step ensures that the ignition process is efficient, supporting overall engine health and performance.

Inspect the New Spark Plug

Visual Inspection:

Before adjusting the gap, visually inspect the new spark plug for any signs of damage, such as cracks in the insulator or deformities in the electrodes.

A damaged spark plug should be replaced immediately to avoid engine misfires or damage.

Measure the Gap

Using a Spark Plug Gauge:

A spark plug gauge is used to measure the gap between the center electrode and the side electrode. Slide the appropriate thickness gauge between the electrodes to check the gap.

Refer to your lawn mower’s owner manual for the recommended gap specification.

Adjust the Gap if Necessary

Correcting the Gap:

If the gap is too narrow:

Carefully use a gap tool to pry the side electrode away from the center electrode. Do this gently to avoid breaking the electrode.

If the gap is too wide:

Gently press the side electrode closer to the center electrode using the gap tool. It’s crucial to do this delicately to avoid damaging the electrode.

Recheck the Gap:

After adjusting, use the gauge again to ensure the gap matches the manufacturer’s specifications. Repeat the adjustment process if necessary until the correct gap is achieved.

The Importance of Correct Gap Setting

Optimal Engine Function:

The spark plug gap is vital for proper ignition. An incorrect gap can lead to engine misfires, reduced power, increased fuel consumption, and even engine damage.

Ensuring the gap is set correctly helps in maintaining the efficiency and longevity of your lawn mower’s engine.

This careful inspection and adjustment of the spark plug gap play a significant role in your lawn mower’s operational efficiency. Correctly set, the spark plug enhances fuel combustion, which is key to a smooth-running engine.

Step 4: Installing the New Spark Plug

Installing a new spark plug correctly is vital to your lawn mower’s performance.

Proper installation prevents damage to the spark plug and ensures optimal engine function.

Follow these steps to install the new spark plug safely and correctly.

Thread the Spark Plug by Hand

Avoid Cross-threading:

Start by carefully threading the new spark plug into the spark plug hole by hand. This is crucial to prevent cross-threading, which can damage the threads in the cylinder head.

Turn the spark plug clockwise by hand until it cannot turn any further without resistance. This ensures that the spark plug is properly aligned and not cross-threaded.

Tighten with a Spark Plug Socket

Using the Right Tool:

Once the spark plug is hand-tight, attach a spark plug socket to your ratchet.

Tighten the spark plug by turning the ratchet clockwise. When the spark plug feels snug, give it an additional 1/8 to 1/4 turn. This secures the spark plug in place without applying excessive force.

Avoid Over-tightening

Prevent Damage:

Be cautious not to over-tighten the spark plug. Over-tightening can damage the threads of the cylinder head and the spark plug itself, which could lead to issues during the next spark plug change.

If available, using a torque wrench set to the manufacturer’s recommended torque specification can ensure you are applying the correct amount of force.

Confirm Proper Installation

Final Checks:

Once installed, double-check that the spark plug is secure but not overly tightened. A properly installed spark plug should be snug but not forced into position.

Reconnect the spark plug wire by pushing the boot onto the spark plug until it clicks, indicating a secure connection.

By carefully threading and appropriately tightening the new spark plug, you ensure a successful installation that promotes efficient engine performance and longevity.

This straightforward but precise approach helps maintain your lawn mower in top condition.

Step 5: Additional Tips for Spark Plug Maintenance

Maintaining your lawn mower’s spark plug is essential for ensuring that your engine runs smoothly and efficiently.

Regular maintenance can prevent common problems like starting difficulties and uneven engine performance.

Here are some additional tips to keep your spark plug in top condition.

Regular Inspection and Cleaning

Check and Clean Regularly:

Regularly inspect the spark plug for signs of wear or damage, such as carbon deposits, oil residue, or a worn electrode. These issues can impede engine performance.

Clean the spark plug using a wire brush or spray-on cleaner to remove buildup. This helps maintain the spark plug’s efficiency and longevity.

Change the Spark Plug Annually

Preventative Replacement:

Consider replacing the spark plug at least once a year as a preventive measure, even if it seems to be in good condition. Regular replacement ensures optimal engine performance and can prevent unexpected engine issues.

The beginning of the mowing season is a good time to replace the spark plug, ensuring that your lawn mower is ready for use.

Use a Torque Wrench for Installation

Correct Installation:

When installing a new spark plug, use a torque wrench to tighten it to the manufacturer’s recommended specifications. This prevents over-tightening or stripping the threads, which can cause significant damage to the engine.

Always refer to your lawn mower’s manual for the correct torque settings.

Follow the Manufacturer’s Guidelines

Maintenance Schedule:

Check your lawn mower’s user manual for specific recommendations on how often to change the spark plug.

Some manufacturers suggest changing the spark plug every 100 hours of operation or at least once per season.

Adhering to these guidelines can help maintain the mower’s performance and extend its lifespan.

Recognize Signs of Spark Plug Issues

Identify Problems Early:

Be proactive and attentive to signs that may indicate spark plug issues, such as difficulty starting the mower, rough idling, or a noticeable decrease in engine performance.

Addressing these signs early by inspecting or replacing the spark plug can prevent further complications and help maintain engine efficiency.

By implementing these maintenance tips, you can ensure that your lawn mower’s spark plug remains in excellent condition, thereby supporting the overall health and performance of your mower.

Regular care and preventive measures can save time and money by avoiding more significant engine problems down the line.


Changing the spark plug on your lawn mower is a straightforward and crucial maintenance task that significantly enhances the performance and longevity of your equipment.

Regular replacement of the spark plug can stave off issues such as difficult starts, poor fuel economy, and rough idling, ensuring that your mower operates smoothly and efficiently.

By adhering to the steps outlined in this guide, you can confidently change the spark plug on your lawn mower yourself, maintaining its top condition for years to come.

This not only saves you money on professional maintenance but also empowers you to take charge of your lawn mower’s upkeep.

Regularly replacing the spark plug is essential for efficient fuel combustion, which helps extend the life of your lawn mower and ensures it starts easily each time.

Furthermore, this practice contributes to reduced emissions, promoting a more environmentally friendly mowing experience.

Remember, consulting your lawn mower’s manual for specific instructions and safety precautions is always advised, and you should tailor these steps to your particular model.

Taking care of this simple yet impactful task will not only extend the lifespan of your lawn mower but also enhance your yard’s appearance throughout the mowing season.

Embrace this maintenance routine to ensure your mower remains a reliable tool in your lawn care arsenal.