Over time, the fine details of mechanics fade from memory. Unless you had a parent or grandparent walk you through a spark plug gap setting, it’s likely you didn’t even know you should be doing that.
Yes, spark plugs come with a gap, but in reality, that spark plug gap is scarcely the number it is supposed to be for your specific car. There are many factors that affect the spark plug gap range for the plugs, and that minor difference can mean running, running well, and running great.
Your fuel economy will even suffer if not adjusted correctly. Which is why knowing how to set a spark plug gap is so beneficial.
Why Gapping Matters?
Gap on a spark plug is determined by the voltage and amperage created by the ignition coil.
The manufacturer’s specifications are determined at the time the engine was designed and the gap will be found in the vehicle owner’s manual or the emission sticker located beneath the hood.
The distance of the gap is important to an engine’s operation and efficiency. But let’s explain this further for anybody wondering, “What happens when plugs are not gapped properly?”
Inadequately sized spark plug gaps lead to premature wear of the ignition system, battle of the ignition system components, and even cylinder misfire.
When a spark plug’s gap is too wide the ignition system must work harder for it (aid on the ignition system all non-operation of the ignition coil, and the ignition control module to fail).
Occasionally, the spark will be “blown out” of a highly turbulent combustion chambers. Plug gaps that are too small will not allow for sufficient ignition of the air/fuel mix causing loss of power and higher tailpipe emissions.
Do Spark Plugs Always Have to Be Gapped?
Not necessarily. In the early days of spark plugs it was a must to gap the spark plugs before installation. While modern spark plugs are usually pre-gapped for you it still makes sense to verify that the pre-gap setting is equal to the vehicles recommended setting.
Setting the gap is different for each vehicle, however most fall between .028″ and .060″. Be sure to consult the owner’s manual to see what the vehicle’s recommended setting is.
How Do I Gap a Spark Plug?
WARNING: Prior to adjusting the gap, be cautious when handling the spark plug electrode tip as its is very fragile and can break easily resulting in serious engine damage.
If you have any self-doubt in your mechanical repair skills, allow your mechanic to repair it.
#1. Locate A Gap Gauge or Feeler Gauge.
There are a number of different types of tools available to measure the gaps of spark plugs, some are more suitable for modern plugs, which may contain delicate precious metals.
Most tools will also include a flat edge that can be use to bend the bottom electrode on the spark plug to closely adjust the gap.
#2. Clean the Spark Plug.
If you have just pulled it out of a box, it is likely pretty clean, but if it is a plug that has been used in your car, it is advisable to clean it with a clean cloth.
On the tips of spark plugs there may be some whitish soot build up so it is a good idea to have them reasonably clean to give you the most accurate measurement. Never clean a spark plug with an abrasive material.
#3. Measure the Gap by Passing the Tool Through the Electrodes.
Place the selected blade or wire on your gap tool between the electrode tips of the plug or slide the coin or other currency through the electrodes for measurement.
Write down the measurement and compare it to the suggested setting that is included in the owner’s manual.
#4. Make Any Needed Adjustments.
Choose the correct measurement on your gap gauge or feeler gauge. If you can’t get the correct feeler gauge through the gap, then the gap needs to be widened. If the tool runs through the gap and does not touch the electrodes, then the gap is too big and you must narrow the gap.
Use your spark plug gap tool to adjust the gap. You can gently bend the ground electrode in to narrow the gap or bend it out to widen the gap.
Be careful in making adjustments. Don’t bend the electrode more than a few fractions of an inch, it is durable but is not meant to be under a lot of pressure and be mindful you do not strike the center electrode.
If you snap off the bottom electrode, or bend the center electrode from prying on it too much, you will have to buy a new spark plug.
Precious metal iridium or platinum center electrodes can be more delicate when it comes to prying on them, and it is always important to use the right spark plug gapping tool.
#5. Check the Gap Again.
Repeat the adjustment process until the gap tool fits closely in between the electrodes. Be sure to keep checking the gap as you make these slight adjustments as a little pressure goes a long way, and you can easily adjust too much and weaken the ground electrode strap.
Tap or pry a bit and then measure. You are better off working incrementally than trying to force it all in one motion.
How To Gap Spark Plugs Without Tool (Step-By-Step)
Some key maintenance of the spark plug gap is important to the life of your old spark plug when and without tool, it’s best to gap your spark plugs using an appropriate tool, but just in case you don’t have a spark plug gap tool handy, we will show you how to get to the correct gap.
Things you’ll need:
- Manufacturer’s manual
- Coins (penny, dime)
- Screwdriver
Ok with that out of the way, this is how to gap spark plugs without a tool:
- Using the torque wrench, remove the old spark plug. You can a socket wrench too, but a torque wrench is nice as when you install the new set you can set it.
- Remove the spark plug from the ignition system. Don’t damage the spark plug wire or the ignition coil.
- Determine what the spark plug gap is from your vehicle’s manufacturer. You can find this typically in the manufacturers handbook.
- Now compare your recommended gap to the diameter of your penny or dime. A penny is approximately 0.06″ and a dime is approximately 0.053″. If your recommended gap is different than either of these or the size is in between, you probably need to get yourself a spark plug gap gauge or gapping tool.
- If the coin fits within the recommended specification, you can now use it as a gapper. Start by gently slipping the coin between the spark plug gap, check for discrepancy between the setting and the spark plug gap measurement.
- For birthing the gap, use the back side of the screwdriver to gently bend the ground electrode (ground strap) inwards.
- If you have a very narrow gap, you can either CAREFULLY use the coin to push the ground electrode outwards.
- Be very CAREFUL, do not touch the tip of the center electrode.
- If your spark plug gap is within spec and you followed the previous steps; if your still to gap, you should be better off getting a spark plug gapping tool or visit your mechanic.
NOTE: This method is not a recommend practice to do with pricy platinum or iridium spark plugs. Iridium spark plugs should be treated delicately as they bend easily with minimal pressure, which can damage the plugs.
What Happens if You Don’t Gap?
Seriously, the car isn’t running right; you either have spark plugs with the wrong gapping or a cheaper set where the gapping wasn’t adjusted — you are going to run into all kinds of problems.
Some of the know issues are:
- Engine misfiring
- Rough idling
- Engine knocking
- Poor engine performance
- Stalling
- Difficulty starting your engine.
If you have even experienced the symptoms of bad spark plugs, it is almost exactly the same.
If that wasn’t bad enough, the long term durability of your engine could be affected by a incorrectly gapped spark plug.
Final Thoughts
It’s never a bad idea to be equipped with the proper tools when doing routine engine maintenance. However, even when you find yourself without the proper tools, it doesn’t mean you can’t get the job done. With a little creativity and determination, you can always figure out how to make it work.
Hopefully, this guide helped you understand the fundamentals of spark plug gapping, and how to gap spark plugs even without a gapper.
FAQs.
How To Gap Spark Plugs?
Steps to Gap Spark Plugs:
1. Find a suitable gap or feeler gauge.
2. Ensure the spark plug is clean but avoid harsh materials.
3. Use the gauge to measure the current gap and juxtapose it with the ideal gap.
4. If you’re uncertain about how to gap spark plugs, use a dedicated spark plug gapping tool for any necessary tweaks.
5. Handle with care. A slight mishap could harm the electrodes.
6. Recheck the gap until it’s in sync with the suggested range.
What is the best way to gap spark plugs?
Use your spark plug gap tool to adjust the gap. Gently bend the ground electrode in to narrow the gap or bend it out to widen it. Be very careful when making adjustments. Don’t bend the electrode more than a few fractions of an inch.
Do spark plugs need to be gapped?
Maybe. A spark plug part number might fit hundreds of different engines from many different manufacturers. Although the NGK factory will set the gap to a preselected setting, this may not be the right gap for your particular engine.
What is the rule of thumb for spark plug gaps?
Naturally aspirated combinations tend to perform better with a hotter plug that’s gapped from 0.030 to 0.035 inches. Conversely, forced-induction and nitrous-assisted mills are happier with cold spark plugs gapped at 0.020 to 0.025 inches.
Does spark plug gap affect performance?
In most engines, performance will improve when the spark plug gap opens toward the intake valve(s). However, without testing different index positions in an engine on a dyno, it is nearly impossible to determine which index increases performance.