How To Change Motorcycle Spark Plugs


Spark plugs play an integral part of a motorcycle’s performance. Spark plugs also are prone to go bad for different reasons, but are designed to be replaced.

Replacing spark plugs is a simple job, but requires a few steps, the correct tools, and some patience to do it right. If you suspect your motorcycle’s engine needs a tune up, you may be wondering how to change old spark plugs.

How to change motorcycle spark plugs:

  • Buy new spark plugs specified by the manufacturer
  • Remove the spark plug wires
  • Remove old spark plug using socket wrench
  • Inspect the condition of the old spark plug
  • Install new spark plug by hand
  • Torque spark plug with socket wrench
  • Install spark plug wire

Not replacing you spark plugs on time can be detrimental to your motorcycle. This article will teach how to do it correctly and on time so you don’t cause any unnecessary damage to your engine.

Process To Replacing Motorcycle Spark Plugs

Here is how to replace the spark plugs on your motorcycle:

  1. Make sure you have the right spark plugs. Refer to your owners manual for the correct type. If that’s not an option, parts stores or motorcycle shops can help look it up or match a new plug with your old one.
  2. Gather the right tools. For this job, using the right size spark plug socket will save a lot of time and headache. These have a rubber grommet that grips the plug and can be purchased at part stores, hardware stores, or online. Some engines have the plugs concealed under covers or the tank, so have the tools ready to take those off.
  3. Locate the spark plugs and remove the spark plug wires. Motorcycles will typically have between 1 and 4 spark plugs depending on your specific engine type. To remove the wires, firmly pull straight up away from the spark plug.
  4. Using your spark plug socket and a socket wrench, turn the spark plug counter-clockwise. It is important to do this while the engine is cold to reduce burn risks. Also, warm metal expands and will make it difficult to remove the plugs.
  5. Once removed, inspect the condition of the spark plug as it can tell you a lot about how your engine is running. For more on spark plug condition, refer below.
  6. Check the gap of the new spark plug. The gap is critical to a good spark. Refer to your owners manual for specifications, but most spark plugs come pre-gapped. Should it need adjusted, there are gapping tools available at parts stores.
  7. Install the new spark plug by hand. Installing it by hand ensures it won’t cross-thread. Also, install the plug dry–meaning no anti-seize–as this can cause over-tightening.
  8. Once the washer on the plug is seated to the engine, give it ¼-½ a turn clockwise with your socket wrench. It is critical to not over-tighten the plug as it could easily break or strip the threads as well as protrude too far into the cylinder and contact the piston.

Repeat for the other spark plugs, if applicable, and reinstall spark plug wires. Start your engine to ensure everything is running smoothly.

What Is “Spark Plug Gap” And How Do I Check It?

As mentioned above, the gap of your spark plugs refers to the space between the curved metal tip and the pointed electrode tip. This is the gap that the voltage charge jumps across, which ignites the air/fuel mixture. It’s similar to how lightning jumps from the clouds to the earth.

So why does spark plug gap matter? If the gap is too small, there won’t be a big enough spark to generate the required heat to ignite your air/fuel mixture. If there is too much of a gap, the voltage will have difficulty arcing. Both conditions will result in poor performance as fuel is going unburned.

Use a proper spark plug gapping tool to check the gap, which has built-in gauges you insert between the electrodes to measure the gap. Refer to your owner’s manual for specifications for your particular engine. If adjustment is necessary, do not use a screwdriver to bend the electrode, as this can damage the plug. A good spark plug gapping tool will have a keyway to use to safely bend the electrode to the right gap.

When Should I Change My Spark Plugs?

After learning all this, you may be wondering, “When should I change my spark plugs?” There are a couple of answers depending on your situation. 

All spark plugs have a service life as part of general maintenance and upkeep. Whenever possible, refer to the manufacturer’s manual for your specific engine for what your engine needs. Typically, spark plugs should last a long time–around 15,000 miles–but are subject to your riding style. 

An off-road bike takes more abuse than a street bike and may need servicing sooner. If you only ride seasonally, you may never need to change the plugs because they just won’t be used enough to wear out.

With that being said, you should check your plugs regularly as part of a preventative maintenance plan. There is the possibility that the threads of the plug can seize in the engine cylinder head, which would require rebuilding or replacing your engine cylinder head. Regularly removing and inspecting your spark plugs lowers the chance of them seizing in the head and also gives you a chance to learn about how well the engine is running.

What Can I Learn From My Spark Plugs?

Now that you have your new spark plugs in, it’s time to look at the old ones. As mentioned above, the condition of the spark plugs says a lot about the efficiency of your engine as well as potential issues. 

A spark plug with just a thin layer of tan coloring indicates a good running engine. If there is excessive carbon build up, it could indicate a rich condition. This could be due to an improperly tuned carburetor, a poor spark, or dirty air filter.

If there is oil on the spark plugs, this indicates an internal oil leak which should be addressed immediately. Furthermore, a damaged spark plug (bent or broken electrode) indicates that the spark plug was installed incorrectly or that a mechanical failure has occurred; both conditions should be fixed immediately.


Another potential issue with spark plugs is called carbon tracking. This occurs when the white ceramic insulator on the spark plug cracks and allows some of the built up electrical charge to escape, which deposits carbon along those cracks.

It can be diagnosed by finding very thin black or brown streaks on the insulated part of the plug. Carbon tracked plugs should be replaced as they will cause a weak ignition in the engine leading to poor performance.

Why Are There So Many Different Types Of Spark Plugs? Which Should I Use?

There are many different manufacturers of spark plugs and it can be overwhelming to know which to buy. As has been mentioned before, your owners manual will have the best info for what you should get. 

The difference in quality between brands is debatable. It seems like everyone has a brand they like most. If you aren’t worried about being brand loyal, it’s not going to matter too much which brand you go with. However, there are a few things to consider. 

Make sure the thread diameter and pitch is correct for your engine. The diameter refers to the size of the threaded part of the plug. Thread pitch refers to how coarse or fine the threads are. The diameter can be measured using calipers and the pitch can be measured using a thread gauge. This can be useful if you don’t have a technical resource, like a manual, to refer to.

Also, make sure you buy from a reputable source. Buying cheap parts online seems like a dream come true, but may actually result in more problems due to the poor quality of the parts. Good plugs are generally inexpensive, so there is no reason to buy the cheapest ones you can online.

How To Keep Your Spark Plugs In Good Shape

  • The most obvious is using the correct plug for your specific engine.
  • Pay attention to any misfiring, lack of power, or sputtering from your engine. This could indicate a fouled plug that needs replaced.
  • Regularly inspect your motorcycle for any issues, including inspecting the condition of your spark plugs.
  • Have a spare plug and the right tools on hand, just in case.
  • Don’t be intimidated by the task of replacing spark plugs. Again, having the right supplies and a bit of time and patience to take the correct steps makes this a feasible project that will improve the performance and longevity of your motorcycle.

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