Knowing how to replace spark plugs on a tractor, ATV, UTV, or other gas-powered farm machine is an important maintenance skill. Replacing spark plugs can improve engine performance, restore easy starting, increase fuel efficiency, and help prevent engine misfires. Fortunately, learning how to replace spark plugs is a straightforward DIY task that requires only a few basic tools.

Key Takeaways

• Knowing how to replace spark plugs is a simple maintenance skill that can improve engine starting and performance.
• Common signs of worn spark plugs include hard starting, rough running, and reduced fuel efficiency.
• Always use the correct spark plug type and check the gap before installation.
• Basic tools like a socket wrench, torque wrench, and gap gauge are required.
• Replacing spark plugs on tractors, ATVs, and UTVs follows the same general process for most gas engines.

How Spark Plugs Work

While spark plug 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.

Signs Your Spark Plugs Need Replacement

Many farmers don’t think about spark plugs until an engine develops problems. Common signs that it’s time to replace spark plugs include difficult starting (even though the tractor battery is strong), rough idling, engine misfires, reduced fuel efficiency, sluggish acceleration, and loss of power under load. If your tractor, ATV, or UTV exhibits these symptoms and other causes have been ruled out, installing new spark plugs is often an inexpensive first troubleshooting step.

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.

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.

Tools Needed to Replace Spark Plugs

Before learning how to replace spark plugs, gather the proper tools. You’ll typically need a spark plug socket, ratchet or socket wrench, torque wrench, wire feeler gauge or spark plug gap tool, and a clean rag. Some engines may also require extensions or specialty sockets to reach deeply recessed spark plugs. Having the right tools on hand makes the job faster and helps prevent damage to the spark plugs or engine.

How to Replace Spark Plugs: Step-by-Step

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:

1. Allow the engine to cool completely.

Do not replace spark plugs when the engine is hot; let the machine sit until the engine is fully cooled.

2. Disconnect the battery.

Once you’re ready to begin, unhook the battery for safety.

3. Remove spark plug wires or ignition coils.

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.

4. Clean debris around each spark plug.

Clean around each spark plug so debris won’t fall into the combustion chamber when you remove the plug.

5. Remove the old spark plugs.

Then, using a socket wrench of the correct size, unscrew and remove each spark plug.

6. Check and adjust the spark plug gap.

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.

7. Install the new spark plugs.

After confirming the gap is correct, carefully thread the spark plugs into place.

8. Tighten to the manufacturer’s torque specification.

Tighten with a torque wrench to the required torque, which will likely be detailed in your machine’s instruction manual.

9. Reinstall wires or coils.

Once the spark plugs are in place, reinstall the spark plug wires or ignition coils.

10. Reconnect the battery and test the engine.

Frequently Asked Questions About Replacing Spark Plugs

How often should spark plugs be replaced?

Replacement intervals vary by manufacturer and spark plug type. Copper spark plugs generally wear faster than platinum or iridium plugs. Always consult your owner’s manual for recommended service intervals.

Can I replace spark plugs myself?

Yes. Learning how to replace spark plugs is considered a beginner-friendly maintenance task on many tractors, ATVs, UTVs, and other gasoline-powered equipment.

What happens if spark plugs are not replaced?

Worn spark plugs can lead to hard starting, poor fuel economy, rough engine operation, reduced power, and increased engine misfires.

Do diesel tractors have spark plugs?

No. Diesel engines use compression ignition instead of spark ignition and therefore do not require spark plugs.

Final Thoughts

Learning how to replace spark plugs is a simple maintenance skill that can improve engine performance, fuel efficiency, and reliability. Whether you’re working on a tractor, ATV, UTV, or other gas-powered farm equipment, replacing worn spark plugs can often solve starting and running issues before they become bigger problems. With the proper tools and a few basic steps, you can keep your equipment operating at its best.

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