What Spark Plug To Use For A Lawnmower?

There are several components of a lawnmower, and a spark plug is one of the most important ones. Much like cars and other fuel utilizing machines, a lawnmower’s engine needs a spark plug for ignition. Without a spark plug, the machine won’t work. It is responsible for igniting the compressed air-fuel mixture in the combustion cylinder to create the energy needed for the machine to start. 

Several types and sizes of spark plugs are readily available in the market today. While all spark plugs generally function using the same principle, there are different types and sizes for different machines. A car and a lawnmower may use spark plugs, but that doesn’t necessarily mean they’ll use the same type. 

This article will provide you with what you need to know about what spark plug to use for your lawnmower.

The ideal spark plug to use for a lawnmower is a small engine spark plug. It has small threads suitable for lawnmower engines. The thread size and thread length are very important in a spark plug. Hence, it’s important to ensure that its thread size is about 10 to 12mm and the thread length is about ⅜ inches. It’s best to check your machine manual to be sure about the right spark plug size for it. 

Components Of A Spark Plug 

Deciding what Spark plug to use for your lawnmower is a critical detail that shouldn’t be overlooked. It’s important to use the right type and size in your lawnmower’s engine to ensure that it works properly. Using a spark plug that’s too big or too small would result in an engine malfunction. 

lawn mower spark plug

Spark plugs have several components that work together to ignite the fuel in the cylinder of your lawnmower’s engine. These components or features vary in measurements or across the different types. A clear description of these components would help you comprehend their importance and how making the wrong decision could damage your plug, engine, or both. 

As mentioned before, all fuel-powered engines require a spark plug for ignition. The spark plugs used for a car’s engine could be used for a lawnmower’s engine. However, this isn’t always the case. The two different machines often need spark plugs with different physical characteristics. 

As a home lawnmower, you might not know all the components of a spark plug, but have a general idea of what’s important. Terms like hot, cold, short, and long are used to explain the characteristics of a spark plug. We can take a closer look at its components below. 

  • A Metal Casing: 

The metal casing is usually a threaded shell. The threads of a spark plug lawnmower are usually threaded. 

  • A Central Electrode:

The central electrode is usually connected to the ignition coil’s output terminal by a thickly insulated wire. It contains an insulator. 

  • An Insulator:

The insulator insulates the terminal, center shaft, and center electrode from the housing, preventing the escape of high voltage from the electrodes. 

  • A Ground Electrode:

Just like the other components of a spark plug, the ground electrode is very important. It improves ignition performance. 

Apart from the items listed above, a spark plug has several other important components, some of which include; a ring, packing washer, center shaft, glass seal, and gasket. All these work together to make it work perfectly. Hence, choosing a lawnmower spark plug should be based on the specifications of these components. 

How To Choose The Right Spark Plug For Your Lawnmower

There are a few things to put into consideration before selecting a spark plug for your lawnmower. Some of these things include;

Spark Plug Size

When selecting a spark plug for your lawnmower engine, size is an important factor to take into consideration. One of the few characteristics that distinguish a lawnmower spark plug from a car engine spark plug is the size. Car engine spark plugs are usually larger than those used for lawnmower engines. 

old spark plug

The thread size of the plug is also very important. Thread sizes must be identical to fit them together. They simply won’t fit if the sizes aren’t identical. You could destroy the spark plug, engine, or both if you try to force threads of different diameters together. 

Most car engines are fitted with a spark plug that has a thread size of appropriately 14mm. On the other hand, lawnmower engines are usually fitted with spark plugs that have a thread size of 10 to 12mm. This is something to keep in mind when you want to get a new spark plug for your machine. 

Spark Plug Thread Length

This is another important factor to take note of when you’re looking to buy a new spark plug. In comparison to car engines, lawnmower spark plugs have shorter thread lengths. The threads on car engine plugs are typically a half-inch to ¾inches long. Lawnmowers, on the other hand, often use spark plugs of ⅜inch length. 

Spark Plug Gap

A spark plug has two electrodes; a central electrode and a ground electrode. The gap between the two electrodes is known as the plug gap. Spark travels from the central electrode to the ground electrode through the spark plug gap. The spark plug gap can always be adjusted to the specifications given by the manufacturer. This can be found in the engine manual. 

Where To Buy The Right Spark Plugs For Your Lawnmower

Spark plugs are very common and easy to find. They are relatively inexpensive and can be gotten almost anywhere as they’re vital engine components. You can always check your lawnmower engine’s required specifications or use the Internet, but the real question is where to get them from. 

Engine spare parts stores are a good place to look for them. Also, you should be able to get a spark plug at a lawnmower store, as they are very likely to sell spare parts.

Another option is to purchase them online on shopping websites. Don’t forget to select the spark plugs with the right specifications.

When Should You Change A Spark plug?

  • Misshapen Physical Appearance

Upon physical inspection, if it is noticed that the spark plug is distorted or damaged, it should be changed immediately. Managing the damaged plug would eventually damage the machine itself. It is rendered useless if the cap, electrode, gap, or flat top is distorted.

  • Excessive Fuel Consumption

If your lawn mower is consuming more fuel than it should, it most likely has something to do with a faulty spark plug. The spark plug should be changed immediately to save cost and avoid more damage.

  • Poor Engine Performance

Your machine won’t perform as it ought to if there’s a problem with the spark plug.

Spark Plug Types And Gaps

The following are types of spark plugs that can be used for lawnmower engines;

  • The standard resistor spark plug has a gap of 0.03 inches
  • The electromagnetic suppression spark plug has a gap of 0.030 inches

How To Change A Spark Plug

  • Locate the spark plug.
  • Disconnect the spark plug head and clean around it with a neat rag, to remove the debris. 
  • Using a spark plug socket, remove the spark plug. Special spark plug sockets usually have rubber inserts to protect the ceramic body of the plug. However, if one isn’t available, a regular one would suffice. 
  • Check the gap on the spark plug. If necessary, use a spark plug gauge to check the gap on the plug and adjust it to the size specified in your machine’s manual. 
  • Replace the old spark plug with the new one.
  • Install the spark plug head. 
spark plug on mower


Can I use a car engine spark plug in my lawnmower?

The answer to this isn’t simple or straightforward. In some circumstances, but not all, car engine spark plugs and lawnmower spark plugs are interchangeable. Thread diameter, thread lengths, gaps, and other characteristics differ between the two varieties. As a result, use a spark plug that matches the criteria listed in the manual of your lawnmower.

Can I Change The Gap On My Spark Plug Myself?

You don’t need any special qualifications to change your spark plug yourself. You can do it by yourself in the comfort of your garage.

How Do I Adjust The Gap On My Spark Plug? 

All you need is a feeler gauge from your toolbox, and you’re good to go. Check the thickness of the gap with your gauge and adjust it until it meets the requirements. If the gap is too wide, gently press the gapped side against a hard surface. If the gap is too narrow, on the other hand, carefully pry the gap open by placing the hole on the spark plug gauge over the ground electrode. Re-measure the gap and make adjustments until it’s the right size. Be careful not to put too much pressure on it to avoid breakage. 

Where Is The Spark Plug Of My Lawnmower Located?

Spark plugs are usually located near the front of the engine. However, on zero turns, you’ll find them at the back, near the sides. They’re easy to access and replace. 

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