How to Replace Spark Plugs on a Tractor, ATV or UTV

Replacing Spark Plugs is a Relatively Straightforward Task You Can Handle Yourself With the Right Tools

by J. Keeler Johnson
PHOTO: Replacing spark plugs on a small tractor. Photo by J. Keeler Johnson

Knowing how to replace spark plugs on a tractor, ATV, or UTV is a useful skill for any farmer to have. While spark plugs don’t require the regular maintenance schedule of other engine components, from time to time replacing spark plugs is a quick solution to engine troubles.

Fortunately, replacing spark plugs is a relatively straightforward task you can handle yourself, provided you have the right tools.

How spark plugs work

While spark plugs designs can vary, the basic principle is always the same. At the bottom of a spark plug are two electrodes (a central electrode and a side or ground electrode) with a narrow gap between them. During operation of the engine, a spark passes between the two electrodes, causing the fuel and air mixture inside the combustion chamber to ignite. This creates gas pressure that pushes on a piston, and the movement of the piston is converted into the rotational energy of the engine.

There’s a spark plug for each piston in a gasoline engine. Diesel engines don’t have spark plugs since they ignite fuel with compression rather than sparks.

When to replace spark plugs

Spark plugs can go for years without needing attention. But if you’re having trouble starting an engine (even though the tractor battery is strong), or if an engine runs rough once it gets going, the spark plugs may be to blame. Replacing the spark plugs can restore the engine to proper working order and also improve fuel efficiency.

Choosing the right spark plugs

Some small gasoline engines might have only a single piston and spark plug. Larger ones have several. And unsurprisingly, spark plugs come in different sizes. The diameter and the distance between the electrodes are two important considerations.

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The material from which the tips of the electrodes are made (copper, platinum, or iridium) can impact performance and longevity. Copper spark plugs have been around for ages, but platinum and iridium spark plugs last longer and may be necessary for high-performance engines. This is especially true of double platinum and double iridium spark plugs, which are designed with platinum or iridium on both electrodes rather than only the central one.

Fortunately, an average farmer doesn’t need to know the nuances of spark plug designs. Simply consult the instruction manual of your machine for a recommendation on the number and type of spark plugs you need.

How to replace spark plugs

The exact steps required to replace spark plugs may vary depending on your engine. Consulting the instruction manual for specifics is a wise idea, but the basics are as follows:

Do not replace spark plugs when the engine is hot; let the machine sit until the engine is fully cooled. Once you’re ready to begin, unhook the battery for safety.

Locate the spark plugs and remove either the spark plugs wires or the ignition coils, depending on whether your engine has spark plug wires or the “coil on plug” (COP) design. Be careful not to damage them, and keep track of which wire/coil goes to which spark plug.

Clean around each spark plug so debris won’t fall into the combustion chamber when you remove the plug. Then, using a socket wrench of the correct size, unscrew and remove each spark plug.

Before installing new spark plugs, you may need to confirm that the spacing between the electrodes—the “gap”—is correct. There are tools available to check the gap and adjust the spacing of the electrodes if needed. A wire feeler gauge or wire gap gauge is what you’re after.

After confirming the gap is correct, carefully thread the spark plugs into place and tighten with a torque wrench to the required torque, which will likely be detailed in your machine’s instruction manual. Once the spark plugs are in place, reinstall the spark plug wires or ignition coils, and don’t forget to hook up the battery.

Congratulations! Now you know how to replace spark plugs on tractors, ATVs, UTVs, and other gas-powered farm machines. And the process is much the same for gas-powered cars, so even a bit of automotive maintenance is now within your reach.

This article about how to replace spark plugs was written for Hobby Farms magazine online. Click here to subscribe. 

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