Mower spark plugs generally have a pitch of 1mm to 1.5mm and a thread size of 10mm to 12mm, with a thread depth of 9,, to 12mm.
Lawn mower maintenance is essential to keep your lawn mower running smoothly and efficiently. A well-maintained mower is going to last longer. A critical aspect of lawn mower maintenance is the spark plug, which is vital in the engine’s combustion process. Choosing the right size of the spark plug can make a significant difference in the performance and efficiency of your lawn mower.
In this beginner’s guide, we will demystify lawn mower spark plug sizes and help you choose the right size for your lawn mower. We will also provide a step-by-step guide on changing it and offer maintenance tips.
Whether you are a first-time lawn mower owner or a seasoned pro, this comprehensive guide will help you understand the importance of the sizes of spark plugs and how to keep your lawn mower running smoothly.
What is a Spark Plug and Why is It Important?

A spark plug is a crucial component of a lawn mower’s engine that creates the spark needed to light the fuel and air mixture in the combustion chamber.
The spark plug transfers the high-voltage electricity from the ignition coil to the engine cylinder, creating a spark that ignites the fuel mixture and powers the engine.
Spark plugs are vital to the combustion process and are responsible for maintaining the engine’s performance and efficiency.
A faulty or worn spark plug can result in lots of issues, including a mower that won’t move, reduced engine power, decreased efficiency, and costly engine damage.
Spark plugs typically consist of four main parts: the shell, insulator, electrodes, and terminal. The shell is the metal exterior of the spark plug that screws into the cylinder head.
The insulator is the ceramic part that isolates the center electrode from the shell. The center electrode is the part of the spark plug that extends into the chamber and delivers the spark. The terminal is the spark plug part that connects to the ignition coil wire.
Understanding Spark Plug Sizes
Sizes for spark plugs are designated by a combination of numbers and letters representing various dimensions and features of the spark plug. Choosing the right size for your lawn mower ensures optimal performance.
The numbers and letters on a spark plug typically include the thread size, reach, seat type, heat range, and electrode gap. The thread size refers to the diameter of the threads that screw into the cylinder head. The reach refers to the length of spark plugs that extends into the combustion chamber.
The seat type refers to the shape of the sealing surface that contacts the cylinder head. The heat range refers to the spark plug’s ability to dissipate heat and maintain an appropriate temperature range. The electrode gap refers to the distance between the center and ground electrodes, which affects the component’s ability to ignite the mixture.
Different spark plugs are available, including standard, copper core, platinum, and iridium spark plugs. Each type has its advantages and disadvantages regarding cost, performance, and durability.
For example, platinum and iridium spark plugs typically last longer than standard or copper core spark plugs but are more expensive.
Choosing the correct riding or push mower spark plugs is crucial for optimal performance. It is essential to consult your lawn mower’s owner manual or a professional to determine the correct size for your specific model.
Like an oil-soaked air filter, using the wrong spark plug size can lead to poor performance, reduced efficiency, and even engine damage, causing difficulty starting the mower.
How to Determine the Right Spark Plug Size for Your Lawn Mower

Determining your lawn mower’s correct size is essential for optimal performance. Here are some steps you can take to choose the correct size spark plug for your lawn mower:
#1. Consult Your Lawn Mower’s Owner Manual
The owner manual typically includes information on your specific model’s proper spark plug size and type. Look for the section on lawnmower maintenance or engine specifications to find the correct lawn mower spark plug size.
#2. Check the Current Spark Plug
Check the numbers and letters on the spark plug’s insulator if you have the old one. These numbers and letters indicate the spark plug’s dimensions and features. They can help you determine the correct replacement spark plug.
#3. Use a Spark Plug Reference Chart
If you do not have the owner manual or the old spark plug, use a spark plug reference chart to determine the correct lawn mower spark plug size. These charts typically require entering your lawn mower’s make and model. They will provide you with the right spark plug type and size.
When choosing the correct lawn mower spark plug size, it is also essential to consider factors such as the type of fuel used, altitude, and climate. Some spark plugs may be better suited for specific types or weather conditions.
Using the correct lawn mower spark plug size can help maintain optimal engine performance and prolong the lifespan of your lawn mower. If you are unsure which size to use, consult a professional or your lawn mower’s manufacturer for guidance.
Changing the Spark Plug
Changing spark plugs in lawn mowers is a simple process that can help maintain optimal engine performance. Here is a step-by-step guide on how to change your lawn mower’s spark plug:
- Turn off the engine and disconnect the spark plug wire: Ensure the engine is turned off and the spark plug wire is disconnected.
- Remove the old spark plug: Use a spark plug socket and ratchet wrench to remove the existing spark plug. If it is difficult to remove, try spraying some penetrating oil around the base to loosen it.
- Check the new spark plug: Before installing the new one, check the numbers and letters on the insulator to ensure it is the correct size and type for your lawn mower.
- Install the new spark plug: Use the socket and ratchet wrench to install the replacement spark plug carefully. Be sure not to overtighten the spark plug, which can damage the threads or insulators.
- Reconnect the spark plug wire: Reconnect the spark plug wire to the top of the spark plug.
- Start the engine and check for proper operation: Start the engine and listen for any unusual sounds or vibrations. If the engine runs smoothly, you have successfully changed the spark plug.
As mentioned earlier, changing the spark plug in your lawn mower is a simple process that can help maintain optimal engine performance.
Getting a replacement every season or after every 100 hours of operation is recommended. This ensures your lawn mower runs at its best.
Maintaining Lawn Mower Spark Plugs
Here are some tips for maintaining your lawn mower spark plug:
Clean the Spark Plug

Over time, the spark plug can become dirty or fouled with debris, affecting its performance. Use a wire brush or cleaner to remove dirt, grime, or carbon buildup from the spark plug’s electrodes.
Check the Electrode Gap
The electrode gap is the distance between the center and ground electrodes on the spark plug. Use a spark plug gap tool to check and adjust the electrode gap. A too-large or small gap can affect the spark plug’s ability to ignite the mixture.
Replace the Spark Plug
Spark plugs can wear out over time and may need to be replaced. As mentioned earlier, getting a replacement every season or after every 100 hours of operation is best to maintain optimal engine performance.
Use the Correct Spark Plug
I can’t emphasize this enough: using the correct size and type for your mower is crucial for maintaining optimal engine performance. Consult your lawn mower’s owner manual or a professional to determine the correct spark plug for your specific model.
Store the Lawn Mower Properly
When storing your mower for an extended period, removing the spark plug and adding a small amount of oil to the cylinder is recommended. This can help prevent corrosion and ensure it is ready when you start the engine again.
Following these tips can help maintain your mower and ensure optimal engine performance.
Final Thoughts
Spark plugs are crucial components of lawn mowers and play a significant role in their proper functioning. Understanding spark plugs’ sizes and determining the right size for your mower is essential for maintaining optimal engine performance.
Following the tips outlined in this guide, you can ensure that your lawn mower’s spark plug is in good condition and running at its best.
Always consult your lawn mower’s owner manual or a professional if you have any questions or concerns about your lawn mower. Happy mowing!