The Seasoned Wrench


Harley Spark Plug Gap Chart: A Guide for Experienced Riders

Chase Manhattan Avatar

Last Updated:

Note: My posts may contain affiliate links. If you click on these links and make a purchase, I may receive a small commission at no extra cost to you. I only recommend products I genuinely believe in. Thanks for supporting The Seasoned Wrench!

Read my full affiliate disclaimer >>

Experienced Harley riders know that spark plugs are a crucial component of their motorcycle’s engine. Spark plugs provide the necessary spark to ignite the fuel mixture, which in turn powers the engine. However, in order for spark plugs to function optimally, they must be set to the correct gap. This is where the Harley spark plug gap chart comes into play.

The Harley spark plug gap chart is a tool that helps riders determine the correct gap for their spark plugs. The chart takes into account the make and model of the motorcycle, as well as the type of spark plug being used. It is important to note that different spark plugs may require different gaps, so it is essential to consult the chart before making any adjustments.

By using the Harley spark plug gap chart, riders can ensure that their spark plugs are set to the correct gap, which will result in optimal engine performance. This small adjustment can make a big difference in the overall performance of the motorcycle. So, whether you are a seasoned rider or a new Harley owner, it is important to familiarize yourself with the spark plug gap chart to ensure that your motorcycle is running at its best.

Related reads:
Who Manufactures Harley Davidson Spark Plugs? (Surprising)
Best Spark Plugs for Harley Davidson Twin Cam: Full Guide
Best Spark Plugs for Harley Davidson Evo: Bikes Evolve Today
Finding The Best Spark Plug Wires for Harley Davidson Bikes

Spark plugs are an essential component of a motorcycle’s ignition system. They are responsible for igniting the air-fuel mixture inside the engine cylinder, which in turn powers the motorcycle. A spark plug consists of several components that work together to produce a spark.

Overview of The Different Components of a Spark Plug

The components of a spark plug include the center electrode, the ground electrode, and the insulator. The center electrode is the part that protrudes into the combustion chamber and produces the spark. The ground electrode is the part that is in contact with the cylinder head and helps to dissipate heat. The insulator is the part that separates the center electrode from the ground electrode.

Touching On The Different Types of Spark Plugs

There are three main types of spark plugs: copper, platinum, and iridium. Copper spark plugs are the most basic and have a short lifespan. Platinum spark plugs last longer than copper spark plugs, but they are more expensive. Iridium spark plugs are the most advanced and have the longest lifespan. They are also the most expensive.

The heat range of a spark plug is another important factor to consider. The heat range refers to the spark plug’s ability to dissipate heat. A spark plug with a high heat range can dissipate more heat than a spark plug with a low heat range. It is important to choose the right heat range for your motorcycle to ensure optimal performance.

In conclusion, understanding the basics of spark plugs is essential for maintaining a motorcycle’s ignition system. Choosing the right type of spark plug and heat range is crucial for optimal performance.

Related resource: Harley Davidson Shock Adjustment Chart: An Experienced Guide

Harley-Davidson motorcycles require regular maintenance to ensure they run at their best. One important aspect of this maintenance is ensuring that the spark plug gap is set correctly. The spark plug gap is the distance between the center and ground electrode of the spark plug and is critical to the proper functioning of the motorcycle’s engine.

Harley Spark Plug Gap Chart by Engine

Engine ModelSpark Plug GapRecommended Spark Plugs
Twin Cam Engines.040″H-D Standard 6R12, Champion RA8HC, NGK DCPR7E, etc.
80 CID Evolution.040″H-D Standard 5R6A, Champion RN12YC, NGK BPR5ES-11, etc.
Sportster Engines.040″H-D Standard 6R12, Champion RA8HC, Autolite 4164, etc.
Shovelhead Engines.040″H-D Standard 5RL, Champion RN13LYC, Autolite 2585, etc.
Milwaukee-Eight Engines.038″ – .042″Specific plugs per model, often NGK or Screamin’ Eagle
Revolution Max Engines.028″ – .031″Typically high-performance plugs, such as NGK or Denso Iridium

Spark Plug Gap for A Few Different Models

The spark plug gap for Harley-Davidson motorcycles can vary depending on the specific model. Here are some of the most common Harley-Davidson models and their spark plug gap specifications:

  • Shovelhead 1975-1981: 0.025 – 0.030 inches
  • Shovelhead 1982-1984: 0.040 – 0.045 inches
  • Sportster: 0.040 – 0.045 inches
  • Evo 1340: 0.038 – 0.042 inches
  • V-Rod: 0.038 – 0.042 inches
  • XR 1000: 0.025 – 0.030 inches

It is important to note that these are general specifications and that the specific spark plug gap for a particular Harley-Davidson model may vary slightly. Always consult the motorcycle’s owner’s manual or a trusted mechanic to ensure that the correct spark plug gap is set.

Adjusting the Spark Plug Gap

Adjusting the spark plug gap on a Harley-Davidson motorcycle is a relatively simple process. Here are the basic steps:

  1. Remove the spark plug from the engine using a spark plug socket.
  2. Use a spark plug gap tool to measure the gap between the center and ground electrode of the spark plug.
  3. Adjust the gap as necessary by gently bending the ground electrode with a spark plug gap tool.
  4. Reinstall the spark plug and torque it to the manufacturer’s specifications.

It is important to note that the spark plug gap should always be adjusted when the engine is cold. Additionally, never attempt to adjust the spark plug gap on a motorcycle that is running or has recently been running.

In conclusion, setting the correct spark plug gap is an important aspect of maintaining a Harley-Davidson motorcycle. By following the manufacturer’s specifications and adjusting the gap as necessary, riders can ensure that their motorcycle runs at its best.

When it comes to selecting the right spark plug for your Harley, there are a few things to consider. The spark plug is an essential component of the engine, and selecting the right one can optimize performance and improve fuel efficiency.

Spark Plug Material Choices

There are several different materials used in spark plugs, including copper, platinum, and iridium. Iridium spark plugs are the most expensive but are also the most durable and provide the best performance. NGK, Champion, Bosch, Autolite, and Denso Iridium are all reputable brands that produce high-quality spark plugs for Harley motorcycles.

Spark Plug Thread and Size

The thread and size of the spark plug are also important factors to consider when selecting the right one for your Harley. The thread size is usually either 10mm or 12mm, and the length can vary depending on the model of the motorcycle. It is important to check the owner’s manual or consult with a mechanic to ensure that you are selecting the correct size and thread for your Harley.

When selecting the right spark plug for your Harley, it is essential to consider the engine type and the specific needs of your motorcycle. By choosing the right spark plug, you can optimize performance, improve fuel efficiency, and ensure that your Harley is running smoothly.

When it comes to Harley spark plug gap chart, installation and maintenance are crucial for optimal performance and fuel efficiency. Here are some tips to ensure proper installation and maintenance of your spark plugs.

Installing New Spark Plugs

Before installing new spark plugs, it is important to check the gap to ensure it matches the manufacturer’s specifications. Using a spark plug gap tool, adjust the gap as necessary. It is recommended to use a torque wrench to tighten the spark plugs to the manufacturer’s recommended torque specification. Over-tightening can damage the threads, while under-tightening can cause misfires.

Spark Plug Maintenance Tips

Regular maintenance of spark plugs is essential for optimal performance and longevity. Here are some tips to keep your spark plugs in good condition:

  • Check the spark plug gap periodically and adjust as necessary.
  • Inspect the spark plugs for signs of wear, such as cracks, erosion, or fouling.
  • Replace the spark plugs if they are worn or damaged.
  • Use only high-quality spark plugs that are recommended by the manufacturer.
  • Avoid using electronic ignition systems that are not compatible with your spark plugs, as this can cause misfires and other issues.
  • Avoid running the engine too lean, as this can cause the spark plugs to overheat and fail prematurely.

By following these installation and maintenance tips, you can ensure that your Harley spark plugs are in good condition and performing optimally.

Infographic chart used to assess the condition of the spark plugs on Harley Davidson motorcycles.

Experienced Harley owners know that spark plugs are an essential component of their motorcycle’s engine. However, even the most well-maintained motorcycles can experience spark plug issues. In this section, we will explore two common spark plug issues that Harley owners may encounter and how to resolve them.

Identifying and Resolving Misfires

A misfire is a common issue that occurs when the spark plug fails to ignite the fuel-air mixture in the combustion chamber. Misfires can cause a variety of problems, including reduced engine performance, poor fuel economy, and increased emissions.

To identify a misfire, riders should look out for symptoms such as rough idling, engine hesitation, and a loss of power. Once a misfire is identified, the rider must first determine the cause of the problem. Common causes of misfires include a faulty spark plug, a damaged ignition coil, or a clogged fuel injector.

To resolve a misfire, riders should begin by replacing the spark plug. If the problem persists, they should check the ignition coil and fuel injector for damage or clogging. Riders should also ensure that the spark plug gap is set correctly according to the manufacturer’s specifications.

Dealing with Spark Plug Fouling

Spark plug fouling is another common issue that Harley owners may encounter. Fouling occurs when the spark plug becomes coated with deposits from the combustion process, which can cause the spark plug to misfire or fail to ignite the fuel-air mixture.

Fouling can be caused by a variety of factors, including a rich fuel mixture, low-quality fuel, or excessive idling. Riders can identify fouling by looking for symptoms such as a rough idle, reduced engine performance, and increased emissions.

To resolve fouling, riders should first identify the cause of the problem. If the fuel mixture is too rich, riders should adjust the carburetor or fuel injection system to reduce the amount of fuel being delivered to the engine. Riders should also use high-quality fuel and avoid excessive idling. In severe cases, the spark plug may need to be replaced.

In conclusion, spark plug issues can cause a variety of problems for Harley owners. By identifying and resolving misfires and fouling, riders can ensure that their motorcycle’s engine is performing at its best.