10 Best Spark Plugs for Harley Davidson | Buying Guide 2022

Do you know what makes Harley ultra-unique from the other bikes? It’s the deep roaring of the throttle!

Nothing is as ecstatic as that sound, almost intoxicating the more you synchronize the speed.


Is that the faint sputtering noise you hear again? It is a huge letdown, especially on a freeway! But it is also a subject of concern because the issue is with the ignition.

You need that punching electricity flowing into the engine once more with the best spark plugs for Harley Davidson.

We don’t have time for chitchat – there is a lot to cover about these small, tough-looking critters. Let’s get on to it right now!

List of Spark Plugs for Harley Davidson:

Best Spark Plugs for Harley Davidson 

It is not just the poor engine running experience you should watch out for. Sometimes the devil of a bad spark plug prompts the ignition not to run at all! Then there is the rough start or idling, decreased gas mileage, etc.

1. E3 Spark Plugs E3.36 Powersports Spark Plug, Pack of 1

E3 Spark Plugs E3.36 Powersports Spark Plug, Pack of 1

The E3.36 Powersports is the best type of spark plug for Harley Davidson. You have got to agree with me here!

Here is a quick feature preview – the plug comes with 5/8 in. hex, gap size of .040 in, and 12 mm thread size. It offers a healthy combustion pressure because of the ground electrode in DiamondFire.

As a result, you will experience better fuel economy, rapid starts, enhanced power output, and minimal emissions.

It does not end here, though. You can install it effortlessly on the Harley year model you own – better be a V-Twin engine!

Nevertheless, the spark plug may not fit motorcycles with a wider OEM gap. Then there is the risk of compromising the efficiency if you sort to manual increase.

Still, the little device stays true to the claimed longevity and durable quality due to the nickel-plated copper electrode.

Highlighted Features:

  • DiamondFire Patented technology for optimal heat transfer
  • Incorporates cold heat range for greater performance
  • The core is copper; the top material is alloy steel
  • 5/8 in. hex, 12 mm thread size, and .040 in. gap size
  • Improved throttle response 3%-6%
  • Lowers carbon emissions
  • Expected to last for 100k miles; 5k Ohm resistor

2. NGK Iridium IX DCPR7EIX Spark Plugs, Twin Cam (Pair)

NGK Iridium IX DCPR7EIX Spark Plugs, Twin Cam

NKG is another company that manufactures some of the best iridium spark plugs for Harley Davidson. This generic design is compatible with many applications.

Of course, you must check the gap requirement prior to sealing the seal of the plug. The gasket-type seat comes with 12 mm threads; hence it offers a 5k Ohm resistor.

Its reach is 19 mm alongside the .031 in. gap. The spark plug has a smaller diameter center electrode to minimize voltage necessity.

Moreover, the overall build quality is superior to last for thousands of miles. The pre-gapped pair has a copper core and a tip from iridium alloy. Even the center electrode made from fine wire offers a superb melting point because of the nickel construction.

The trivalent metal plating has corrugated ribs and uses a pure alumina silicate ceramic insulator.

All in all, these spark plugs are an example of extreme resistance toward high thermal activity. Therefore, the overall design allows long-term knocking and vibration withstanding features.

The shell plating provides improved anti-corroding qualities as well.

Highlighted Features:

  • Pre-gapped, 5k Ohm resistor type
  • 25% smaller iridium electrode
  • Miniature diameter minimizes voltage
  • Smaller center electrode prolongs ignition life
  • Enhances 2HP engine power
  • Incorporates 5/8 in., hex, 12 mm threads, 19 mm reach, and .031 in. gap
  • Copper core with iridium tip for increased performance

3. Iridium Performance Spark Plugs Pair, Harley# 6R12

Iridium Performance Spark Plugs Pair, Harley# 6R12

Another recommended spark plugs pair is the Iridium Performance by Orange Cycle Parts manufacturer. It is suitable for the Softail Slim twin cam from Harley Davidson (2000-2017; 6R12).

The metal shell provides distinctive black ceramic with the addition of a golden coating. It ensures long-lasting resistance against corrosion to operate better.

Its traditional J-style technology offers iridium electrodes, known for their smaller design than the standard ones. This is why you can expect very little voltage facilitation but extensive igniting power.

The pair comprises .042 in. gap size, 12 mm thread, 17 mm reach, and 5/8 in. hex size. Plus, the resistor type ensures quick firing with proper fuel burning to reduce carbon emission in the long run.

You can ride for thousands of miles without worrying about fouling. Just make sure the gap fits properly to avoid engine sputtering. Some might find the installation a little time-consuming.

Besides, the spark plugs develop enhanced throttle response, an advantage that surpasses most minor issues.

Highlighted Features:

  • Supports removable terminal nut
  • Projected insulator tip
  • A smaller electrode made from iridium; less voltage requirement
  • 5/8 in. hex, 12 mm thread, 17 mm reach, and .042 in. gap
  • Resistor type spark plugs; comes in pair
  • Hotter spark technology for fast ignition; improves performance
  • Anti-corrosion properties via black ceramic and gold-coated metal shell

4. E3 Spark Plugs E3.34 Powersports Spark Plug, Pack of 1

E3 Spark Plugs E3.34 Powersports Spark Plug

The E3.34 is also one of the best performance spark plugs for Harley Davidson thatis equally sought out as the previous E3 unit.

It is not about comparison but compatibility that matters. The plug is super cheap to utilize in high-performing engines like V-twin.  

There are only the dimensions differences; the rest of the characteristics are still the same. Nevertheless, it’s okay to mention the work of DiamondFire ground electrode twice for its excellent function.

It also lets the engine start immediately, giving a short period to the voltage application. The patented technology helps reduce fuel consumption, increase engine power, and more.

Furthermore, it offers resistor-type operation with the incorporation of a gasket seat. The dimensions include 13/16 in. hex, 14 mm threads, 19 mm reach, and a .030 in gap size.  

It also comes with the nickel-plated copper electrode, an energy-efficient feature that facilitates greater heat transfer. With the help of the two legs to the shell, the level of intense vibration resistance is improved.

As a result, the spark plug is highly durable with a 100k miles runtime guarantee.

Highlighted Features:

  • DiamondFire ground electrode configuration
  • 13/16 in. hex, 14 mm threads, 19 mm reach, and .030 in. gap
  • Reduces carbon emissions; offers fuel efficiency
  • Faster flame propagation for smooth acceleration/idle
  • Associates high heat dispersal
  • Projected insulator tip
  • Alloy steel top material with copper core

5. NGK 6046 DCPR7EIX Spark Plugs

NGK 6046 DCPR7EIX Spark Plugs

It is entirely impossible to ignore the best ngk spark plugs for Harley Davidson, the 6046 DCPR7EIX. Many Harley owners with V-twin engines have relied on their assured quality to experience a smoother ride on the roads.

Plus, if it can enhance the engine power, even to a fraction, the product deserves a place on this list. The pair can replace the OEM plugs effortlessly.

It comes with the 11/16 in. hex size alongside the 12 mm thread. The 19 mm reach and 0.031 in. gap makes it an excellent fitment for Harley 103.

Other notable characteristics entail rapid ignition, superb anti-tangling, and outstanding throttle response. This is why the NGK 6064 is considered one of the popular spark plugs to enhance performance.

Consequently, it offers an excellent cold heat range to provide a high melting point. The heat dispersing level is quite reliable, allowing a strengthening effect for durability.

Each spark plug also features triple coating to improve electrode operation and prevent leakage. The core is constructed from iridium material to ensure optimal performance without engaging in much voltage.

However, the only issue lies with fuel consumption is decreasing the efficiency. Additionally, the adjustments seem a little fragile, so be careful during installation.

Highlighted Features:

  • High melting point integration
  • Iridium core for enhanced performance
  • 11/16 in. hex, 12 mm thread, 19 mm reach, .031 in. gap
  • Triple seal incorporation for anti-leak
  • Smaller electrode design for the fast ignition system
  • Ideal for twin cam, V-twin engines in HD
  • The gap is adjustable for correct suitability

6. Champion Iridium 9701 Spark Plug (Carton of 1)

Champion Iridium 9701 Spark Plug

Any champion spark plug guide you obtain will deliver the precise instruction for you to install it without a fuss. As a result, Champion is yet another name, pretty well known among the bikers/tuning experts.

It maintains a reliable operating temperature at any engine load, making the platinum ground electrode perform better. This helps the engine to improve during ignition as well as throttling function.

Now, the dimensions comprise the traditional 5/8 in. hex, 12 mm thread with 19 mm reach, and a .040 in. gap size. Despite being slightly costlier than the rest of the spark plugs, many users recommend this unit for one reason.

It features a fine-wire iridium center and platinum V-trimmed ground electrode. The combo produces the sharpest spark focus, leading to supreme engine performance with greater mileage.

Plus, the electrodes can reach the optimal temperature quickly due to the heat-active alloy.

Highlighted Features:

  • Metal top with iridium core
  • A platinum ground electrode (V-trimmed) for sharp spark performance
  • Fantastic throttle response, ignition start
  • Iridium center has a fine wire that is laser locked
  • 5/8 in. hex, 12mm thread, 19mm reach, a .040 in. gap
  • Exclusive heat-active alloy for better high heat range
  • Incorporates 8-heat range; 5k Ohm resistor 

7. Accel 2418 Spark Plugs (Pair) 6R12

Accel 2418 Spark Plugs (Pair) 6R12

This bespoke design of the Accel 2418 spark plugs is a perfect fit for twin cam 1450/1550cc engines from 1999 to 2021. The higher the RPM reaches, the better performance the pair will give your Harley-Davidson motorcycle.

It offers a .040 in. gap size with 12 mm thread and 19 mm reach. The ideal dimensions make it a perfect match for many racing and standard bikes as well.

What makes it special is the U-design in the electrode region that generates a wider and hotter spark. It is fast and free of taking up more voltage than needed. Besides, it threads quickly with a fast gapping function.

The only problem is some Harley models may not come with their specifications. So, replacing them when on the road can be tricky without the right tools.

This pair uses the purest form of copper and nickel alloy electrodes. As a result, the heat range can perform at a broader level to prevent fouling. The heat is capable of dissipating.

Moreover, you will be impressed with the increased throttle response and elimination of flashover and overheat.

Highlighted Features:

  • Produces hotter and wider spark due to U-groove ground electrode
  • The electrode is built from premium copper/nickel alloy
  • Prevents flashover with heavy-duty 5 rib insulators
  • Resistant to dissipation and foul
  • 12 mm thread, 19 mm reach, and .040 in. gap
  • Minimizes misfires and emissions
  • Improves throttle response and engine efficiency

8. Harley-Davidson Original Equipment Spark Plug, RG6HCC

Harley-Davidson Original Equipment Spark Plug, RG6HCC

So, you want to stick to the stock parts. The best Harley spark plugs bythemotorcycle company are highly reliable.

With their pre-gapped setup, all you will have to do is get the right tool and install it then and there. Of course, you must know what you are doing!

It has one of the most commonly used thread sizes of 10 mm with the standard 5/8 in. hex., a gap of .031 in and 19 mm reach. This OE-style product is nothing like the conventional ones that run out of time after a few thousand miles.

You can be on the road for as long as 50k miles (always inspect the plug at 10k or 15k miles) with a new stock spark plug. Plus, it restores the throttle response to its original state while making the engine run smoother without misfires.

It also provides excellent heat range to avert fouling after a certain period. You will also notice a sealing property to keep leakage at bay, making complete combustion each time you start.

Highlighted Features:

  • It comes with a pre-gapped design at .031 in
  • 5/8 in. hex, 10 mm thread, and 19 mm reach
  • High-quality electrode alloy material for full combustion
  • Wide heat range to maintain fouling, short out, and knocking
  • Eliminates misfires
  • Improves throttle responses due to fast ignition
  • Superior construction to deliver serious power

9. NGK Iridium Spark Plugs, CR9EIX

NGK Iridium Spark Plugs, CR9EIX

Once again, the NGK iridium takes over the spot of the best spark plugs for Harley Davidson, and I amnot even surprised.

While the cost may leave you short of more than ten bucks, it is totally worth the money. NGK provides supreme technology for its spark plugs, including the iridium core and nickel top electrode structure.

The iridium conveys brilliant operation for the 25% smaller electrode design. It extends ignition life while reducing voltage amount at the same time.

Also, the anti-corrosion qualities are top-notch due to the new metal shell plating. There is zero chance of leakage, and the broad heat range allows the engine to be in an intense condition without compromising the thermal performance.

The plugs are greatly compatible with V-Twin engines by Harley-Davidson motorcycles.

Highlighted Features:

  • Iridium core with top nickel electrode
  • Smaller electrode offers better starting properties
  • 5/8 in. hex, 10 mm thread, 1 9mm reach, .030 in. gap
  • Optimal heat range to avoid fouling
  • Minimizes carbon emission
  • Increases fuel efficiency with lower voltage function
  • It offers great gas mileage



I choose NOS OEM Harley Gold spark plugs for the last option as it offers many amazing features. The gold-palladium tip ensures you have more lifespan in the plugs than expected.

Their state-of-the-art spark plug technology and overall design make this product a popular choice among HD owners. You will notice the tips are tapered so that the combustion function is at max.

Each spark plug delivers a concentrated spark with fast action. It lets the device be stable in idle situations. There is a special coating to the thread that offers protection against seizing.

Even the shell has a triple coating for absolute elimination of corrosion. All in all, the copper-cored ground electrode and the other prominent characteristics deliver top-notch functionalities after installation.

Highlighted Features:

  • Gold-palladium tip to extend the life
  • Copper cored electrodes for high electric conductivity
  • Offers superior throttle response, mileage, and heat range
  • Coated thread for anti-seize protection
  • Triple coated shell for anti-corrosion
  • Pre-gapped with 5/8 in. hex, 12mm thread, and 19mm reach
  • The tapered tip allows maximum combustibility

Things to Check Before Getting One

You cannot just go to the workshop and tell the mechanic to set up a random spark plug for the precious Harley. They will laugh at you – no doubt in that.

This particle range of bike models requires specific brands, as reviewed above. Most importantly, a few factors must come to light before buying the little instrument.


If the details are absent in the manuals, it gets a step trickier to figure out the Harley Davidson spark plugs of the right size. This is where the Vernier Calipers enter the scene.  

Spark Plugs

Measure the thread size, hex size, and thread reach to obtain the correct item for your Harley model.

Heat Range

First, heat range indicates how fast the heat transference works between the sparking region to the cooling system. This quick operation also determines the withstanding capability and duration of combustion temperature.

So, it is a big deal for the bikes if you want smooth ignition and engine function. Too cold a spark plug may lead to fouling, whereas too hot may be the cause of serious engine damage.

Spark Plugs for Harley Davidson

Remember that high heat dispersal is the cold type (high heat range) and low heat dispersal is the hot type (low heat range).

Choose the one that offers numerous ranges!


From the best spark plug wires for Harley Davidson to thematerials each plug is reinforced with, never neglect the quality review when buying online.

Most spark plug material electrodes have copper, silver iridium, or platinum construction.

However, silver is not as popular as the rest, so let me explain in detail below:

Quick Rundown of Electrode Types

You have to know which material fits the best for your Harley to ensure dynamic longevity and hassle-free lightning-fast ignition power. I have settled the materials from low to high price factor here:

  • Copper

It is the most standard and affordable form that provides the best conduction to electricity. Copper is the way if you want a cost-saving option and obtain something that does not overheat.

Spark Plugs for Harley Davidson

Conversely, they have terrible runtime. Speaking from experience, copper erodes naturally after only some thousand miles of operation.

  • Platinum

There are two kinds of platinum spark plugs – single and double. Let’s start with the single, slightly costlier than the copper-tipped ones, yet they have lower conductivity despite their amazing resistance against erosion and wearing. They have better durability but with a light matter of overheating.

The double-platinum spark plugs, on the contrary, offer a double-plated tip. As a result, expect them to last longer than the single platinum. You can already guess that they have a higher price tag as well.

Also, platinum double or single does not matter because you will experience overheating issues with both. 

  • Iridium

Iridium is terrible at conducting electricity, but it does not ignore the other performing features.

Spark plugs of this material can easily outlast all of the above options and deliver a service life of about 40k to 80k!

The bad news is they are expensive.

Spark Plugs


That tiny gap between the electrodes is what makes the engine start. Hence, the size is important.

The spark might be too weak to run the engine properly if the gap is smaller. A bigger gap width may fail to ignite the electrical current.

1. E3 Spark Plugs E3.36 Powersports Spark Plug, Pack of 1

Harley Davidson Spark Plug Gap Chart

Product NameMaterialEngineHex Size Thread DiameterThread ReachGap Size
E3 Spark Plugs E3.36Nickel (top), Copper (Core)V-Twin5/8 in12 mm19 mm0.040 in
NGK Iridium IX DCPR7EIXMetal (top), Nickel (core)Twin Cam5/8 in12 mm19 mm0.031 in
Iridium Performance, Harley# 6R12Ceramic (top), Iridium (core)Softail Slim, Twin Cam5/8 in12 mm17 mm0.042 in
E3 Spark Plugs E3.34Nickel (top), Copper (core)V-Twin13/16 in14 mm  19 mm0.030 in
NGK 6046 DCPR7EIXIridium (core)V-Twin11/16 in12 mm19 mm0.031 in
Champion Iridium 9701Metal (top), Iridium (core)V-Twin, Twin Cam5/8 in12 mm19 mm0.040 in
Accel 2418, Harley 6R12Copper (top), Copper (core)Twin Cam12 mm19 mm0.040 in
Harley-Davidson Original Equipment, RG6HCC15-later XG, 17-later Milwaukee-Eight5/8 in10 mm19 mm0.031 in
NGK Iridium Spark Plugs, CR9EIXNickel (top), Iridium (core)V-Twin5/8 in10 mm19 mm0.030 in
NEW NOS OEM HARLEY GOLD, 32356-94Copper (core)V-Twin5/8 in12 mm19 mmPre-gapped

E3 Spark Plugs vs. NGK

The E3 and NGK are two of the most popular manufacturers that expert tuners prefer before anything else. Let’s see how exceptional they are.

E3 Spark Plugs

E3 Spark Plugs

  • They are the leading choice as the best Harley spark plugs
  • It fits perfectly into a wide range of bike models
  • Diamond-shaped electrode grade to stimulate turbulence in air/fuel mixtures
  • The shell includes ground electrode while the insulator consists of a terminal connection and the middle wire
  • Greater fuel efficiency; minimizes carbon emission
  • Delivers powerful cycles of sparks with better consistency
  • Reduction in metal fatigue and erosion allows faster fuel-burning simultaneously
  • Minimal voltage; resists rust and corrosion
  • Enhances engine life


  • One of the most preferred choices among many highlighted companies
  • Minimizes electrical quenching effect
  • Superb igniting capability, thanks to the iridium alloy tip design
  • Prevents fouling, resists seizing and corrosion
  • Known for superior and robust quality
  • Users experience better throttle performance
  • Reduce engine misfires but increases acceleration and durability
  • Low maintenance

The Verdict

Although both companies produce high-end spark plugs for Harley, I pick E3 for its vast versatility and power. Yes, NKG enhances the engine firing with similar attributes, but the E3 spark plugs are all about fuel efficiency and longevity.

Honestly, it is a tough decision to make! Don’t curse me if I did not pick your favorite.

Frequently Asked Questions

1. What kind of spark plugs do I need for Harley Davidson?

Spark plugs are not universal for Harley models, so you should inspect the entire specification chart before buying one.

While all the products listed above are compatible with the named bike, you must ensure it fits the particular model based on the year model.

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

What do you need in the spark plug performance? It is the long-lasting effect that necessitates hardiness.

In that case, iridium claims to be almost six times harder than platinum! Moreover, it is about eight times tougher, and you will notice fine electrodes. It has fantastic wear-resisting qualities and offers a 700˚ greater melting point.

However, platinum is cheaper to purchase while holding that sharp edge better than conventional spark plugs.

3. Are NGK plugs suitable for Harley Davidson?

Yes, they are consistent with high-quality, optimized performance and are recommended by many HD enthusiasts.

4. Are E3 spark plugs suitable for Harley Davidson?

The E3 spark plugs are quite popular with various motorcycle models, including the good old Harley. You can attain enhanced engine ignition quality if the right size is selected.

5. Do iridium spark plugs increase performance?

Here are some significant benefits of iridium spark plugs to give you some ideas:
• Superb melting point
• Produces better electrodes
• Retains wearing characteristics
• Top-notch performance than conventional ones
• Reliable longevity
• Prevents frequent replacements
• Delivers fast ignition

6. What happens when the spark plug gap is too wide?

You will experience engine misfires when riding the bike at high speed. There is also the issue of improper firing, dragging, etc.

7. How can I set the spark plug gap on my Harley motorcycle?

After checking the bike specifications, it is time to pick a gap tool to set things right. There are three types – a coin-type, a blade-type, and a wire-type.
Now, clean the spark plug, place/pass the tool between the electrodes gap and adjust accordingly.

8. Does the spark gap of my Harley increase over the usage time?

Yes! Each time you fire the engine, a tiny amount of metal from plugs is getting removed due to the spark. Thus, the voltage also increases to ignite the engine the next time. However, this wearing process happens very slowly.

9. How often should I change my Harley Davidson spark plugs?

It is suggested that you replace the spark plugs seasonally or after every 10k miles. Some even change them after 20k miles, depending on the spark plug quality, of course.

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

If the air/fuel mixture is leaner or you prefer high RPM, go for cold. Otherwise, you will have to face carbon deposits accumulation on the spark plug tip, leading to fouling (short out).

The rich air/fuel mixture calls for hot units if the bike operates at low RPM. They have good insulators that avert heat transfer in the water jackets and allow self-cleaning.

Final Words

These are the best spark plugs for Harley Davidson that will enhance and transform your riding performance to the max.

Just remember to check them after every 10k miles. Good luck and enjoy the healthy vroom sound!

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