How To Gap A Spark Plug: 8 Steps (with Pictures) - WikiHow

Home » How To Spark Plug Gap » How To Gap A Spark Plug: 8 Steps (with Pictures) - WikiHow

Maybe your like

Skip to ContentQuizzes
  • Home
  • Random
  • Browse Articles
  • Quizzes & Games
  • All QuizzesHot
  • Love Quizzes
  • Personality Quizzes
  • Fun Games
  • Dating Simulator
  • Learn Something New
  • Forums
  • Courses
  • Happiness Hub
  • Explore More
  • Support wikiHow
  • About wikiHow
  • Log in / Sign up
Terms of Use wikiHow is where trusted research and expert knowledge come together. Learn why people trust wikiHow How to Gap a Spark Plug PDF download Download Article Co-authored by Jason Shackelford

Last Updated: December 17, 2025 Fact Checked

PDF download Download Article
  • Measuring the Gap
    • |
  • Adjusting the Gap
    • |
  • Video
    • |
  • Q&A
    • |
  • Tips
    • |
  • Warnings
    • |
  • Things You'll Need
|Show more |Show less ARTICLE VIDEO X

This article was co-authored by Jason Shackelford. Jason Shackelford is the Owner of Stingray Auto Repair, a family owned and operated auto repair shop with locations in Seattle and Redmond, Washington. He has over 24 years of experience in auto repair and services, and every single technician on Jason’s team has more than 10 years of experience. There are 7 references cited in this article, which can be found at the bottom of the page. This article has been fact-checked, ensuring the accuracy of any cited facts and confirming the authority of its sources. This article has been viewed 595,190 times.

A properly gapped spark plug is necessary for a properly functioning engine. The gap size affects the spark plug's firing temperature, which has a direct relationship to the combustion of fuel and air in the engine. Opening the gaps provides a larger spark, useful for some customized engines in maximizing the efficiency. You can learn to properly gap spark plugs by measuring and adjusting accordingly.

Steps

Part 1 Part 1 of 2:

Measuring the Gap

PDF download Download Article
  1. Step 1 Learn your vehicle's gap specifications. 1 Learn your vehicle's gap specifications. Whether you're shopping for new plugs, you just bought new plugs that you want to check before installing, or you want to check the function of your current set of spark plugs, you need to learn the appropriate gap between the two electrodes on the end of each plug.
    • Each vehicle's measurement will be different, though most are generally somewhere between 0.028-.06 inch (0.15 cm). You can either look in your owner's manual or go to the auto parts store and have them look it up for you.
    • Modified engines require smaller gap settings to account for the amount of power you're putting through the engine. General rule of thumb: the more power, the smaller the gap.
  2. Step 2 Select an appropriate gap tool. 2 Select an appropriate gap tool. There are several varieties of tools used to measure the gaps of spark plugs, some of which are more appropriate for more modern plugs, which sometimes feature delicate precious metals. Most measuring tools will also feature a flat edge typically used for bending the bottom electrode on the spark plug to adjust the gap slightly.[1]
    • A coin-style gap measure is usually the cheapest option, and works by running the edge of the "coin" through the gap until you reach a point where it stops. The edge is marked like a ruler, designating the thickness of the edge at that point. This is a good tool for older plugs you want to check the efficacy of, but can also inadvertently widen the gaps as you use it.
    • A wire coin gap works essentially the same way as the regular coin-style gap, but features different wire measures of varying lengths on the edge around the coin.
    • A blade-style feeler gauge is an effective and versatile tool. Built like a pocket-knife, this gauge features different blades of varying widths, some with wire on the end and some without, placed in the gap to check the spacing of the electrodes. You can also use multiple blades to measure larger gaps. These are effective to use while adjusting.
    Advertisement
  3. Step 3 Clean the spark... 3 Clean the spark plug. If you've just pulled it out of the box, it should be in pretty good shape, but if you're checking a plug that you've been using in your car it's a good idea to clean it off a little with a clean cloth. Spark plugs can build up some whitish soot on the contact points, so you'll want to make sure they're somewhat clean to get the most accurate reading.[2]
    • You can use a little bit of quick-drying (90%) alcohol on the contact points to clean them off if they're especially dirty.[3] Lots of build-up or any blackening on the contact points might be a sign of a plug that's outlasted its prime, however. If they're especially dirty, you might consider buying new ones.
    • There's a special tool designed for cleaning spark plug—think of it as a sand-filled pouch that's attached to an air compressor. It cleans the electrode of the spark plug by sandblasting it.
  4. Step 4 Measure the gap by passing the tool through the electrodes. 4 Measure the gap by passing the tool through the electrodes. Place the appropriate blade or wire on your gap tool between the electrode tips of the plug, or pass the coin through the electrodes to determine the measurement.
    5. Advertisement
Part 2 Part 2 of 2:

Adjusting the Gap

PDF download Download Article
  1. Step 1 Determine if the gap needs adjusting. 1 Determine if the gap needs adjusting. If the tool passes through the gap without touching the electrodes at the appropriate measure, your gap is too wide. If you can't fit it between the electrodes, the gap is too small and needs to be widened some. If it fits closely to the specified measurement, you're safe to install the spark plug.[4]
    • Most spark plugs and iridium plugs manufactured today don't need to be gapped prior to installing them. If you've got a custom modified engine, though, you might be interested in checking or installing plugs at a different spacing. Adjust them accordingly.[5]
  2. Step 2 Use the tool to adjust the bottom electrode. 2 Use the tool to adjust the bottom electrode. When you hold the spark plug with the electrodes facing the floor, you'll want to bend the bottom one very gently either in toward the other electrode if you want to narrow the gap, or out, if you want to increase the gap slightly.[6]
    • Never bend more than a few (.02) fractions of an inch. It won't take much pressure, so be very careful. Spark plugs can be quite delicate, and any fracturing can cause misfires.
    • If you're having trouble using the tool to adjust the gap, consider bending it in using a flat surface like a table to apply some very gentle pressure on the electrode to adjust it.
  3. Step 3 Re-measure the gap and adjust accordingly. 3 Re-measure the gap and adjust accordingly. Be very careful not to contact the electrode in the center of the plug and damage the core. If it breaks or shorts you'll need to toss it and buy a new one.
  4. Step 4 Be very gentle. 4 Be very gentle. Snapping off the electrode will waste your efforts, and it doesn't take much to do so. Use only a small amount of pressure to bend the electrode and only bend it a little bit.
    5. Advertisement

Community Q&A

Search Add New Question
  • Question The gap for my car is .054. This is more than double the thickness of the thickest blade on a feeler gauge. Am I supposed to remove several blades from the feeler-gauge assembly and stack them? Community Answer Community Answer Yes. Add more to get the right thickness, if your thickest leaf is too small. It's a very accurate way to measure or set a gap. Thanks! We're glad this was helpful. Thank you for your feedback. If wikiHow has helped you, please consider a small contribution to support us in helping more readers like you. We’re committed to providing the world with free how-to resources, and even $1 helps us in our mission. Support wikiHow Yes No Not Helpful 4 Helpful 11
  • Question How would I know if my plug is pre-gapped? Community Answer Community Answer It says on the inside flap of the box whether or not they're pre-gapped. Thanks! We're glad this was helpful. Thank you for your feedback. If wikiHow has helped you, please consider a small contribution to support us in helping more readers like you. We’re committed to providing the world with free how-to resources, and even $1 helps us in our mission. Support wikiHow Yes No Not Helpful 5 Helpful 18
  • Question How do I find the gap on an NKG spark plug? Community Answer Community Answer NGK offers an extensive pocket book, which is often given away for free at exhibitions and motor fair. You can usually find this sort of information on NKG's website as well. The correct gap depends on the motor type and may vary from the gap when buying it new. Thanks! We're glad this was helpful. Thank you for your feedback. If wikiHow has helped you, please consider a small contribution to support us in helping more readers like you. We’re committed to providing the world with free how-to resources, and even $1 helps us in our mission. Support wikiHow Yes No Not Helpful 23 Helpful 26
See more answers Ask a Question 200 characters left Include your email address to get a message when this question is answered. Submit Advertisement

Video

Read Video Transcript

Tips

  • Do not over-tighten the spark plugs.[7] Most heads are made of aluminum and the threads can strip easily. Thanks Helpful 0 Not Helpful 0
  • If the color of the tips are different from one another, your engine may have a problem. Thanks Helpful 4 Not Helpful 0
  • Try to match the gaps between all plugs as evenly as possible. Thanks Helpful 3 Not Helpful 0
Show More Tips Submit a Tip All tip submissions are carefully reviewed before being published Name Please provide your name and last initial Submit Thanks for submitting a tip for review! Advertisement

Warnings

  • Be sure to re-install the plug wires in the same order as they were before. Thanks Helpful 57 Not Helpful 14
Advertisement

Things You'll Need

  • Feeler gauge
  • 13/16" socket with drive
  • Vice
  • Rag

You Might Also Like

Change Spark Plugs in a CarHow to Remove & Install Spark Plugs Read a Feeler GaugeHow toRead a Feeler Gauge Clean Spark PlugsHow toClean Spark Plugs Read a Spark PlugHow toRead a Spark Plug Use an Ignition Spark TesterHow toUse an Ignition Spark Tester Test Spark Plug WiresHow toTest Spark Plug Wires Replace Spark Plug WiresHow toReplace Spark Plug Wires Know if a Spark Plug Is Bad7 Symptoms of a Bad Spark Plug Do a Compression TestHow toDo a Compression Test Test an Ignition CoilHow toTest an Ignition Coil Measure Cylinder BoreHow toMeasure Cylinder Bore Adjust TimingHow toAdjust Timing Test Glow PlugsHow toTest Glow Plugs Measure a Gauge PiercingHow toMeasure a Gauge Piercing Advertisement

References

  1. ↑ https://pubmed.ncbi.nlm.nih.gov/36844584/
  2. ↑ https://fctemis.org/notes/9933_SERVICING%20OF%20SPARK%20PLUG.pdf
  3. ↑ https://www.youtube.com/watch?v=c-o_3RNOYzc
  4. ↑ https://www.researchgate.net/publication/348060415_Platinum_Spark_Plug_Gap_Adjustment_to_Fuel_Consumption_and_CO_Emission_at_110cc_Engine
  5. ↑ https://osme.co.in/wp-content/uploads/2020/04/Spark-Plug.pdf
  6. ↑ https://www.youtube.com/watch?v=IuW3svdqKZM
  7. ↑ https://www.youtube.com/watch?v=Ef1ElCVN64k

About This Article

Jason Shackelford Co-authored by: Jason Shackelford Auto Technician This article was co-authored by Jason Shackelford. Jason Shackelford is the Owner of Stingray Auto Repair, a family owned and operated auto repair shop with locations in Seattle and Redmond, Washington. He has over 24 years of experience in auto repair and services, and every single technician on Jason’s team has more than 10 years of experience. This article has been viewed 595,190 times. 8 votes - 88% Co-authors: 24 Updated: December 17, 2025 Views: 595,190 Categories: Engine Parts Article SummaryX

A spark plug gap is the distance between the end of the electrode and the base of the spark plug. If your spark plugs aren’t properly gapped, your engine may not burn fuel properly. Since every make and model requires a different gap size, start by looking in the owner’s manual for your vehicle to find the required gap size, or pull the information up online. Then, grab a gauge tool, and slide the recessed lip under the electrode sticking out from the base of the spark plug. Rotate the disc until you feel a firm resistance and check the measurement next to the lip. If the gap matches your required size, you’re good to install it in your vehicle. If the gap is too small, pull the body of the plug away from the disc with the electrode hanging on the lip to gently force the gap open and re-measure it. If the gap is too big, use the broad side of the gap tool to push the electrode down and make the gap smaller. Continue re-measuring and making minor adjustments until the gap in the spark plug matches your manufacturer’s recommended gap size. For tips on choosing an appropriate gap tool, read on! Did this summary help you?YesNo

In other languages French Portuguese Russian Spanish Italian Dutch Indonesian Vietnamese Arabic Thai German Czech Japanese
  • Print
  • Send fan mail to authors
Thanks to all authors for creating a page that has been read 595,190 times.

Reader Success Stories

  • Joan F.

    Joan F.

    May 20, 2017

    "Never knew about gapping a spark plug til someone mentioned I should do it before replacing the one in my lawn..." more
More reader stories Hide reader stories Share your story

Did this article help you?

Yes No Advertisement Cookies make wikiHow better. By continuing to use our site, you agree to our cookie policy. Jason Shackelford Co-authored by: Jason Shackelford Auto Technician Co-authors: 24 Updated: December 17, 2025 Views: 595,190 88% of readers found this article helpful. 8 votes - 88% Click a star to add your vote Joan F.

Joan F.

May 20, 2017

"Never knew about gapping a spark plug til someone mentioned I should do it before replacing the one in my lawn..." more Bunny Fuller

Bunny Fuller

Sep 9, 2016

"I've never done this (replace a spark plug in a lawnmower), and found your website very helpful and easy to..." more S Schmeckpeper

S Schmeckpeper

Jul 4, 2017

"I don't like adjusting the gap on spark plugs, but I have an old 1965 Ford, so I have always had to. This..." more Rated this article: Yassin Zuberi Phiri

Yassin Zuberi Phiri

Oct 15, 2016

"This method has really helped so much by learning different tactics. And it's working for sure, thanks guys..." more Melanie VanLeuven

Melanie VanLeuven

Jul 23, 2017

"When you need to adjust the gap on platinum plugs, use the wire gapping tool, do not touch the electrode!" Rated this article: Share yours! More success stories Hide success stories

Quizzes & Games

Music Notes & Symbols TestMusic Notes & Symbols TestTake QuizAm I a Good Kisser QuizAm I a Good Kisser QuizTake QuizEngagement Ring QuizEngagement Ring QuizTake QuizWhat Chakra Do I Need to Balance QuizWhat Chakra Do I Need to Balance QuizTake QuizAm I Smart QuizAm I Smart QuizTake QuizFinish the Phrase QuizFinish the Phrase QuizTake Quiz

You Might Also Like

Change Spark Plugs in a CarHow to Remove & Install Spark PlugsRead a Feeler GaugeHow toRead a Feeler GaugeClean Spark PlugsHow toClean Spark PlugsRead a Spark PlugHow toRead a Spark Plug

Featured Articles

Exercise Your BrainHow toExercise Your BrainBe a Fun Person to Hang out WithHow toBe a Fun Person to Hang out WithWhat Does Your Morning Routine Say About You?What Does Your Morning Routine Say About You?Develop Productive HabitsHow toDevelop Productive HabitsPractice Self CareHow toPractice Self CareWhat Song Matches Your Life Right Now?What Song Matches Your Life Right Now?

Trending Articles

Make OutHow toMake OutHow Rare Is My Birthday QuizHow Rare Is My Birthday QuizWhat Am I Craving QuizWhat Am I Craving QuizIs Your Personality More 6 or 7?Is Your Personality More 6 or 7?What Should My Name Really Be QuizWhat Should My Name Really Be QuizIs a Guy You Don't Know Well Interested in You?Is a Guy You Don't Know Well Interested in You?

Featured Articles

Your 2026 Vision: What Does Next Year Hold?Your 2026 Vision: What Does Next Year Hold?Understanding the Most Attractive Face Shapes (& Determining Your Own)Understanding the Most Attractive Face Shapes (& Determining Your Own)Type A B C D Personality TestType A B C D Personality Test250+ Messages to Reassure Your Partner (For Him & Her)250+ Messages to Reassure Your Partner (For Him & Her)What Is My Favorite Color QuizWhat Is My Favorite Color Quiz215+ Funny & Creative Personalized Vanity Plate Ideas215+ Funny & Creative Personalized Vanity Plate Ideas

Featured Articles

100+ Creative Ways to Say Good Night100+ Creative Ways to Say Good NightWhy Can't I Sleep QuizWhy Can't I Sleep Quiz150+ Love Paragraphs to Make Him Feel Special150+ Love Paragraphs to Make Him Feel SpecialWhat Does Your Tattoo Placement Mean? Spiritual & Aesthetic MeaningsWhat Does Your Tattoo Placement Mean? Spiritual & Aesthetic Meanings19 of the Rarest Wonders from around the World19 of the Rarest Wonders from around the WorldWhat Is the Fun Scale? The 3 Types of Fun & Their BenefitsWhat Is the Fun Scale? The 3 Types of Fun & Their Benefits

Watch Articles

Wrap a Round GiftHow toWrap a Round GiftSteam in an OvenHow toSteam in an Oven Make Plant-Based Meat: 4 Incredible RecipesHow to Make Plant-Based Meat: 4 Incredible RecipesClean a Silver NecklaceHow toClean a Silver Necklace4 Easy Ways to Open a Can of Soda4 Easy Ways to Open a Can of SodaPart Your HairHow toPart Your Hair

Trending Articles

Can We Guess If You're a Cat or Dog Person?Can We Guess If You're a Cat or Dog Person?30 of the Hardest Riddles on Earth: The Harvard Riddle & Beyond30 of the Hardest Riddles on Earth: The Harvard Riddle & BeyondWhich of the Big Three Are Your Parents? (Percy Jackson)Which of the Big Three Are Your Parents? (Percy Jackson) Perform Magic: 8 Tricks for BeginnersHow to Perform Magic: 8 Tricks for BeginnersWhat’s My Personality Based on My K-Pop Taste?What’s My Personality Based on My K-Pop Taste?What School Subject Are You?What School Subject Are You?

Quizzes & Games

Quick IQ TestQuick IQ TestTake QuizWhat's My Hair Type QuizWhat's My Hair Type QuizTake QuizWhat Piercing Should I Get QuizWhat Piercing Should I Get QuizTake QuizWhat Is My Face Shape QuizWhat Is My Face Shape QuizTake QuizWhat Age Is My Brain QuizWhat Age Is My Brain QuizTake QuizWhat’s The Perfect Hair Care Routine For MeWhat’s The Perfect Hair Care Routine For MeTake Quiz wikiHow
  • Categories
  • Cars & Other Vehicles
  • Cars
  • Car Maintenance and Repair
  • Car Engines
  • Engine Parts
wikiHow Newsletter You're all set! Helpful how-tos delivered toyour inbox every week! Sign me up! By signing up you are agreeing to receive emails according to our privacy policy.
  • Home
  • About wikiHow
  • Experts
  • Jobs
  • Contact Us
  • Site Map
  • Terms of Use
  • Privacy Policy
  • Do Not Sell or Share My Info
  • Not Selling Info
  • Contribute

Follow Us

×

Don’t miss out! Sign up for

wikiHow’s newsletter

Subscribe You're all set! X --536

Tag » How To Spark Plug Gap