Best Spark Plugs For Harley Davidson Motorcycles

I. Introduction

A spark plug is tiny, but an important part of your Harley Davidson motorcycle, and a little knowledge about it will help you to keep your Harley motorbike in good health.

In this article we are discussing the topics, viz. what is a sparkplug?, how to select the sparkplug for your Harley Davidson, reviews of the best sparkplugs for Harley Davidson motorcycles on Amazon, buying tips which may help you to purchase the sparkplug, and frequently asked questions.

II. What Is A Spark plug?

The spark plug in your Harley is a simple item, yet highly accurate in its function, and it delivers the spark (across the minute gap) for igniting the compressed gasoline and air mixture at every power stroke.

You can see two metal electrodes (center and side (ground)) at the tip of the spark plug and the electrodes and the gap between them facilitates the generation of the spark under high voltage. Every spark erodes a very minute portion of the electrodes and over time either the gap needs to be adjusted or the sparkplug replaced.

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A spark plug with a higher gap (more than the recommended) will not work efficiently and may lead to misfires, engine running rough, and reduced fuel economy. The life of the sparkplug depends on the material of the electrodes.

Sparkplugs are made with electrodes (both center and ground) of materials that can withstand high engine temperatures, vibration, and wear. The types of sparkplugs (based on the material)-(i) Copper sparkplugs (ii) Iridium sparkplugs (iii) Platinum sparkplugs and (iv) Silver sparkplugs.

Copper and silver sparkplugs have high thermal conductivity but should be replaced sooner, and platinum and iridium spark plugs last longer but have low thermal conductivity.

In the motorcycles of the olden days, sparkplugs used to wear out quickly and the rider always used to keep a spare spark plug. However, the advanced technology used in your Harley Davidson motorcycles makes the sparkplug more reliable and longer-lasting.

It is important to choose a good sparkplug recommended and compatible with your Harley motorcycle.

A good quality sparkplug should have endurance and its tips should withstand a constant rate of sparking. Replace the sparkplugs as recommended in your owner’s manual to keep your Harley healthy and running. Do not wait for the spark plug to fail.

When you inspect the sparkplug, you may get an idea if it is good for use or to be replaced, by noticing its color. Color of light gray indicates the sparkplug is still good to use, dark black color with deposits indicate the sparkplug is very cold for the engine, and a bright white color may indicate overheating.


III. How To Select The Spark Plug For Your Harley Davidson Motorcycle?

Refer to your owner’s manual and note down:

  • Designation of the sparkplug (it can be Harley-Davidson 5R6A, 6R12, etc.)
  • Recommended spark gap- Spark-gap is the gap between the two electrodes and you have to ensure that the gap should be adjustable to your requirement.
  • Hexagon size, thread size (in mm), and length of thread (thread reach). If these details are not given in the owner’s manual, you may have to take out the sparkplug and measure it using Vernier calipers. Thread sizes in the USA can be 10, 12, 14, and 18 mm and the nut sizes vary accordingly. No. of threads or length of thread on the sparkplug indicates the reach (how far it will go into the combustion chamber of the engine). The reach is important since this is the point of spark and ignition of the compressed gas.
  • The heat range of the sparkplug- This is the quickness with which the spark plug can transfer the heat from the sparking area to the cooling system, and indicates the duration for which the sparkplug can withstand the high temperature of combustion.
  • The material of the sparkplug electrode, viz. copper, silver, platinum, iridium, etc. (silver is not popular).

If you are going for a Harley-Davidson sparkplug the designation is sufficient. However, when you are looking for a good spark plug on online stores like Amazon, you should know and use the above details to select a suitable sparkplug for your Harley.


IV. Review Of The Best Sparkplugs For Harley Davidson Motorcycles On Amazon

1. NGK Iridium IX DCPR7EIX sparkplug for 1999-2016 Harley Davidson Twin Cam (Pair). Manufacturer-NGK. Core material-nickel.

  • Comes with a pre-gap setting.
  • NGK iridium electrode is 25% smaller than a platinum electrode spark plug and is 1/4th size of the nickel electrode.
  • A very small diameter center electrode reduces the requirement of voltage. The new plating on the shell has improved the anti-corrosion quality.

User reviews are good. Users used this sparkplug for their 2000 Dyna Super Glide, 2009 Harley (cautioned to use proper tools for gap setting), and 2002 HD Heritage Softail. One user commented that this plug did not work on the Harley Electra Glide classic. User review suggests that you should not gap these plugs (please clarify this before you purchase the sparkplug).

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2. NGK Iridium IX DCPR8EIX sparkplugs for 2006-2016 Harley Davidson V-rod (Pair). Manufacturer-NGK

  • Comes with pre-gap setting
  • NGK iridium electrode is 25% smaller than a platinum electrode sparkplug and is 1/4th size of the nickel electrode.
  • A very small diameter center electrode reduces the requirement of voltage.
  • The new plating on the shell has improved the anti-corrosion quality.

User reviews are positive.

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3. Harley Sportster Roadster XL 1200R (1986 to 2020) Iridium performance sparkplugs pair replacement. OEM # 6R12. Brand-Orange Cycle Parts.

  • Supreme performance with the highest level of technology.
  • Iridium electrode is smaller in diameter and requires less voltage and last longer compared to other sparkplugs.
  • 12 mm thread diameter, 5/8ʺ hexagon, and 11/16ʺ thread reach.

User reviews are good.

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4. Iridium performance sparkplugs pair for Harley Softail Slim Twin Cam (2000 to 2017) replacement. Harley # 6R12. Brand-Orange Cycle Parts

  • Supreme performance with the highest level of technology.
  • Iridium electrode is smaller in diameter and requires less voltage and last longer compared to other sparkplugs.
  • Item model no-OCP0231-AZ3
  • 12 mm thread diameter, 5/8ʺ Hex, and 11/16ʺ thread reach.

User reviews are normally good. Customers have used this on their 2006 Harley Ultra, 2011 Heritage Classic, and 2015 Road King.

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5. E3 sparkplugs power sports sparkplug (E336). Universal fit.

  • Core material-copper. Top material- Alloy steel
  • Designed with colder heat ranges to enable modifications in performance and intense conditions.
  • Thread diameter-12 mm. Hexagon size-5/8ʺ. Reach-3/4ʺ
  • Engineered with a high nickel alloy center and ground electrode for extra life.
  • The presence of Yttrium-enhanced alloy helps reduce inside electrode temperature up to 8% for enhanced durability and less pre-ignition.

User reviews are good. Customers used this for their Harley models-2001 Electra Guide Ultra Classic, 2007 FLSTC, 2004 Screaming Eagle Electra Glide with the 103, 2006 Sportster 883 Low, 2004 Fat Boy, 2001 Sportster, Street Glide, and 1998 Electra Glide. One user wrote that this is a good replacement for HD 6R12 (model E3.36)

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6. Champion sparkplug RA8HC for Harley Davidson Street Glide FLHX/I 2006-2016

A standard Champion brand sparkplug features a wide insulator base for fast heat transfer, a copper core electrode for efficient conductivity.


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7. NGK #6046 Iridium sparkplugs DCPR7EIX for Harley Davidson Twin Cam and XL. Manufacturer-NGK Sparkplugs

User reviews are good. Previous customers used this for their Harley model-Harley FLHTCU, and 2008 Ultra Classic.


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8. NGK Sparkplugs 2115 Iridium IX sparkplug for Harley Davidson Big Twin. NGK sparkplug part #2115


No user reviews but NGK is a reputed brand.


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9. NGK Iridium sparkplug BPR5EIX-11 for Harley Davidson Electra Glide Ultra Classic FLHT/C/U 1983-1999. Brand-NGK


  • Laser welded iridium center electrode tip.
  • Platinum disc welded to the rear side of the ground electrode for long life
  • Improved fuel economy, reduced emissions, faster start, and good acceleration.
  • Superior ignitability and long life.


No user reviews. NGK is a reliable and reputed brand.

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10. Harley Dyna Low Rider performance sparkplugs replacement OEM# 6R12. Brand-Orange cycle parts.


  • Conventional sparkplugs in OEM heat ranges.
  • Black ceramic body, the insulator is made from 95% pure alumina and has a strong resistance to heat shock.

User reviews are good. Customers used this for their Harley models-2005 Dyna Switchback, and 2001 XL 1200.

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11. NGK Iridium sparkplug DCPR7EIX. Fits Harley Davidson Softail Rocker Custom FXCWC (ABS) 2011. Brand-NGK.


NGK is a reliable brand. No user reviews.


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12. Champion RA8WHP (9701) Iridium sparkplug pack of 1.Brand-Champion.

  • Core material-Iridium. Top metal-Metal.
  • This sparkplug has a fine-wire iridium center electrode and platinum ground electrode for maximum performance.

User reviews are good. Customers used this for their Harley model-2013 HD Breakout (FXSB), 2017 HD Softail Slim FLSTC, and 2000 FLSTC.

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V. Buying Tips

  • Keep the information as detailed under ‘III’ ready for your Harley model and select the sparkplug matching these details.
  • If you are planning to upgrade the sparkplug (for example if your Harley is fitted with platinum electrode sparkplugs, and you want to go for iridium sparkplugs), study the implications, and if necessary discuss with your mechanic or in an online Harley users forum. Clear all your doubts before making a decision. Also, when you upgrade the sparkplug, clarify whether you should set the sparkplug gap as per your owner’s manual or as per the sparkplug manufacturer’s.
  • The thread size of the sparkplug, hexagonal size, reach of the sparkplug, spark gap, and heat range are all important. Please ensure this. It is a good idea to place your old sparkplugs and the new sparkplugs side by side and physically compare them before putting them in your Harley.
  • Sparkplugs are designated with codes like-NGK Iridium BPRSEIX-11. Search for the standard designation codes for the sparkplug on the internet to understand this. In the present case, B-indicates the thread size 14mm, P-projecting insulator type, R-resistor, 5-is the heat rating, E-indicates the thread length as 19 mm, IX- indicates Iridium IX sparkplug, and 11- indicates the spark gap as 1.1 mm.
  • Going for a reputed and reliable brand is important. Some of the brands in the market are –ACDelco is an American company owned by General Motors, Bosch is a multinational company having its headquarters in Germany, NGK is a public company in Japan, Champion is a US brand, and Denso is a Japanese brand.


VI. Frequently Asked Questions

1. How often should you replace sparkplugs on Harley Davidson?

Replace the sparkplugs as recommended in your owner’s manual, and also inspect the sparkplug for correct gap and carbon deposition after every 5000 miles.
However, if your Harley engine is running rough, or losing power, or not starting, inspect the sparkplugs, and replace them if necessary.

2. How many spark plugs are there in my Harley Davidson?

Normally Harley Davidson motorcycles have one spark plug in each cylinder, and so if your Harley has a V-Twin engine, there will be 2 sparkplugs in total. However, if your Harley has an M8 engine, then the number of spark plugs is two in each engine, and hence total is 4 sparkplugs.

3. How can I set the sparkplug gap on my Harley motorcycle?

Read and understand your owner’s manual (including the specified spark gap) and take out the sparkplugs using the correct size socket spanner and wrench. Before taking out the spark plug, blow the dust away using compressed air.

You need a thickness gauge (wire gauge is preferred), a gapping tool for correcting the spark gap, and the torque wrench set to the torque recommended in your owner’s manual.
Clean the spark plug (with cleaning spray) and check the spark plug gap using a wire gauge and if necessary, correct the gap using the gapping tool (using a screwdriver to do this may spoil your spark plug). Inspect the spark plug, and if everything looks fine screw it back into the engine first by hand, followed by the socket and torque wrench. Put the electric connection back in place.

4. Does the spark gap of the spark plug in my Harley increase over the usage time?

The electrodes of the spark plug undergo wear due to the regular spark between them and you can reset the gap once or twice, after which the spark plug should be replaced.

5. What happens if the spark plug gap is wider than the specified gap?

When the spark plug gap is wide, the occurrence of the spark may not happen consistently leading to either a rough running engine or an engine not starting at all.

6. Which material spark plug is better, iridium, or platinum?

Iridium is harder and stronger than platinum, and also has a comparatively higher melting point than platinum. Due to these characteristics, sparkplugs with iridium material may last up to 25% longer than sparkplugs with platinum electrodes. However, iridium sparkplugs cost you more than platinum sparkplugs. It is wise to check the recommended sparkplug material in your Harley owner’s manual and stick to it. If you want to go for other material sparkplugs, discuss with an authorized Harley mechanic or in a Harley users forum, before making a decision.

7. Which is the best spark plug material for my Harley motorcycle?

You can find out the recommended spark plug material by Harley by referring to the owner’s manual. It may be wise to stick to the sparkplug material recommended by Harley for your model. However, if Harley has recommended platinum or copper sparkplugs, and you want to upgrade to iridium, please take the advice of your Harley mechanic or discuss in a Harley user forum before finalizing.

8. What is gapping?

Gapping is maintaining the correct gap between the center and the ground electrodes of the spark plug. The correct gap is given in your Harley owner’s manual. When you are looking to purchase new sparkplugs, the recommended gap for your Harley is one of the major specifications you should remember.

9. What do you mean by the heat range for a spark plug?

The heat range of a motorcycle spark plug is the swiftness with which it can transfer the heat from the sparking tip to the cooling system. The heat range is mentioned by a number and its interpretation may differ from manufacturer to manufacturer.

Sparkplugs are normally known as ‘hot plugs’ or ‘cold plugs’. The hot plugs have higher insulator nose lengths (on the spark end) and hence the time required for the transfer of heat from the sparking tip to the cooling system is slow. On the other hand, cold plugs have less insulator nose lengths with a faster transfer of heat from the sparking tip to the cooling system.
Hot plugs are suitable for low rpm engines, and cold plugs are suitable for high rpm engines.

10. Which spark plug should I buy, hot or cold?

Study your Harley owner’s manual, and follow the recommendation. If your owner’s manual does not have the information, you may have to do a physical inspection of the spark plug to know whether it is a ‘hot’ or ‘cold’ type. Also, you can consult your mechanic or an online Harley user’s forum.

11. What is the shelf life of an unboxed spark plug?

A spark plug of a reputed brand, unopened and stored in a cool dry place should be good for use even after 5 or more years. As long as the spark plug is not exposed to the atmosphere, it will not get corroded or deteriorated.

VII. Conclusion

We tend to ignore the sparkplugs since they seldom trouble us. However, they have an important function so make sure to take good care of them.

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