What’s That Gap on My Lawn Mower Spark Plug?

You’re ready to tackle the overgrown lawn, but your trusty lawn mower coughs and sputters, refusing to cooperate. Frustrated, you might suspect the spark plug, that tiny but crucial component responsible for igniting the fuel-air mixture. But before you rush to replace it, take a moment to understand the spark plug gap, a tiny space that plays a massive role in your mower’s performance.

This article will delve into the world of spark plug gaps, explaining their importance, how to measure them, and how to adjust them for optimal performance. We’ll discuss the consequences of a mismatched gap, the tools you’ll need, and how to ensure your lawn mower runs smoothly for years to come. So, let’s get started and understand this critical aspect of lawn mower maintenance.

The Spark Plug Gap: A Tiny Space, A Big Impact

The spark plug gap is the tiny space between the center electrode (the spark-producing tip) and the ground electrode (the metal contact point). This seemingly insignificant gap plays a crucial role in the ignition process. When the spark plug fires, electricity jumps across the gap, igniting the fuel-air mixture in the combustion chamber.

How does the gap affect engine performance?

  • Proper Gap: A correctly adjusted gap ensures a strong, reliable spark that ignites the fuel efficiently. This translates to optimal power, smooth running, and fuel efficiency.
  • Too Wide: A gap that’s too wide weakens the spark, making ignition difficult and potentially leading to misfires, reduced power, and increased fuel consumption.
  • Too Narrow: Conversely, a gap that’s too narrow can cause the spark to jump too easily, resulting in a weak spark, inefficient combustion, and potential damage to the spark plug itself.

Understanding the Spark Plug Gap Specifications

Every spark plug comes with a recommended gap specified by the manufacturer. This gap is critical for ensuring optimal performance and avoiding engine problems. You can find the recommended gap for your specific spark plug on the packaging, the owner’s manual, or online.

Why do manufacturers recommend specific gaps?

  • Engine Design: The spark plug gap is designed to work harmoniously with the engine’s compression ratio, ignition system, and other factors.
  • Fuel Type: Different fuels have different ignition characteristics, requiring specific gap settings for optimal combustion.

Measuring the Spark Plug Gap: A Simple Process

You can measure the spark plug gap using a simple tool called a spark plug gap gauge. These gauges come in different sizes, usually ranging from 0.020 to 0.060 inches.

How to Measure:

  1. Clean the Spark Plug: Use a wire brush or compressed air to remove dirt and debris from the spark plug electrodes.
  2. Insert the Gauge: Insert the correct sized gauge between the spark plug electrodes.
  3. Check the Fit: The gauge should fit snugly between the electrodes without forcing. If the gauge slides through freely, the gap is too wide. If you can’t insert the gauge, the gap is too narrow.
  4. Adjust the Gap (if needed): If the gap needs adjusting, use a specialized tool called a gap tool to bend the electrode slightly.

Important Note:

  • Always refer to your owner’s manual for the correct spark plug gap specifications for your lawn mower.
  • Don’t adjust the gap too much as it can weaken the electrode and shorten the spark plug’s lifespan.

Adjusting the Spark Plug Gap: A Precision Task

If the measured gap doesn’t match the recommended setting, you’ll need to adjust it.

Adjusting the Gap:

  1. Locate the Electrode: Identify the electrode that needs adjustment. Usually, it’s the ground electrode.
  2. Bend the Electrode: Use the gap tool to gently bend the electrode, either inward to narrow the gap or outward to widen it.
  3. Re-Measure: Re-measure the gap using the gauge after each adjustment to ensure it matches the recommended specifications.

Tools You’ll Need:

  • Spark Plug Gap Gauge: To measure the gap.
  • Spark Plug Gap Tool: To adjust the gap.

When to Check the Spark Plug Gap:

Regularly checking the spark plug gap is essential for maintaining optimal engine performance. Here’s when you should consider inspecting the gap:

  • Every Engine Tune-Up: A tune-up typically includes spark plug replacement and gap adjustment.
  • When You Notice Engine Problems: If you experience misfires, reduced power, or difficulty starting, a faulty spark plug gap could be the culprit.
  • After Replacing the Spark Plug: Always check the gap after replacing a spark plug, as it may not be factory set correctly.

The Consequences of a Mismatched Gap

Maintaining the correct spark plug gap is crucial for several reasons:

  • Reduced Engine Power: An incorrect gap can lead to weak sparks, resulting in incomplete combustion and reduced engine power.
  • Increased Fuel Consumption: A mismatched gap can lead to inefficient fuel combustion, leading to higher fuel consumption.
  • Engine Misfires: If the spark plug gap is too wide, the spark might not ignite the fuel-air mixture, leading to misfires.
  • Premature Spark Plug Failure: A gap that is too narrow can cause the spark to jump too easily, leading to premature wear and tear on the spark plug.
  • Damage to the Ignition System: A mismatched gap can strain the ignition system, potentially causing damage.

Keeping Your Lawn Mower Running Smoothly

By understanding the importance of the spark plug gap and knowing how to check and adjust it, you can ensure your lawn mower operates efficiently and reliably for years to come.


  • Always refer to your owner’s manual for the recommended spark plug gap specifications for your specific mower.
  • Use the correct tools for measuring and adjusting the gap.
  • Regularly check the gap to prevent engine issues.

By taking the time to maintain the spark plug gap, you’ll ensure your lawn mower stays in tip-top shape, allowing you to tackle any lawn challenge with ease. So, grab your tools, check that gap, and get ready to enjoy a beautifully manicured lawn!

Frequently Asked Questions

1. What is the gap on a spark plug?

The gap on a spark plug is the small space between the center electrode and the side electrode. This gap is crucial for the proper functioning of the spark plug. It allows for a spark to jump across the gap, igniting the air-fuel mixture in the engine’s combustion chamber.

The gap is measured in thousandths of an inch (thousandths) or millimeters. A correctly sized gap ensures a strong, consistent spark, resulting in optimal engine performance.

2. Why is the spark plug gap important?

The spark plug gap plays a vital role in the ignition process. If the gap is too small, the spark might not be strong enough to ignite the fuel mixture, leading to misfires and reduced engine power. On the other hand, a gap that is too large can result in a weak spark, making it harder to ignite the mixture and potentially damaging the spark plug.

Maintaining the correct gap is essential for efficient combustion, optimal engine performance, and longevity of the spark plug.

3. How do I know what the correct gap is for my lawn mower?

The recommended spark plug gap for your specific lawn mower model is usually listed in the owner’s manual. If you can’t find it there, you can refer to the spark plug’s packaging or consult a reliable online resource. The gap will often be etched on the spark plug itself.

Always follow the manufacturer’s specifications for the correct gap setting to ensure optimal performance and avoid potential engine issues.

4. How can I check the spark plug gap?

You can check the spark plug gap using a specialized tool called a spark plug gap gauge. This tool features various sized blades that allow you to measure the gap between the electrodes. Insert the appropriate blade into the gap, and if it fits snugly, your spark plug gap is correct.

If the gap is too small or too large, you can adjust it by carefully bending the side electrode. Always refer to the owner’s manual or a trusted resource for specific instructions on adjusting the gap.

5. How do I adjust the spark plug gap?

To adjust the spark plug gap, you’ll need a spark plug gap gauge and a pair of pliers. First, identify the side electrode that you need to bend. Gently insert the appropriate blade from the gap gauge into the spark plug gap. If the blade slides through freely, the gap is too large. If the blade doesn’t fit, the gap is too small.

Using the pliers, carefully bend the side electrode closer to the center electrode to decrease the gap, or further away to increase the gap. Once you’ve achieved the correct gap, double-check with the gap gauge.

6. When should I check my spark plug gap?

It’s a good practice to check the spark plug gap every time you replace the spark plug. Additionally, if you notice a decrease in engine performance, misfires, or difficulty starting your lawn mower, it might be time to check the gap.

Even if the spark plug is new, it’s worth checking the gap as it might have shifted during installation or transportation.

7. What happens if I don’t check the spark plug gap?

Failing to check the spark plug gap can lead to a variety of issues, including:

  • Reduced engine performance: An incorrectly gapped spark plug can result in a weak spark, leading to incomplete combustion and reduced engine power.
  • Misfires: A misfire occurs when the air-fuel mixture in the cylinder does not ignite properly. This can be caused by a faulty spark plug or an incorrect gap, leading to rough idling and inconsistent engine performance.
  • Damage to the spark plug: A gap that is too large can cause the spark to arc excessively, damaging the spark plug’s electrodes and potentially creating electrical shorts.
  • Premature wear and tear: A misfiring spark plug can cause premature wear and tear on other engine components, leading to more expensive repairs in the long run.

Regularly checking the spark plug gap ensures optimal engine performance, prevents misfires, and extends the lifespan of your lawn mower’s engine.

Leave a Comment