How to Gap Spark Plugs Without Tool [Easy Solution]

By Jed Lehman •  Updated: 01/26/24 •  9 min read

Wondering how to gap spark plugs without a tool? We have you covered.

A spark plug gap is a distance between the plug’s electrode and the ground strap. Typically, these gaps have variations that are as small as one-thousandth of an inch.

While most spark plugs come with the appropriate gap for combustion, what if the gap is wrong?

A spark plug gap that’s off by a thousandth of an inch can cause your engine to misfire and lead to a decrease in horsepower.

Unfortunately, checking the spark plug gap is not always a simple task. Gapping the spark plug (increasing or decreasing the gap) can also be a lot of work.

There are specific gapping tools made for spark plug gaps, and while most mechanics have access to these tools, they’re not found in most home garages.

The good news is that a spark plug can be gapped with some less conventional tools. We’re going to take you through a handful of spark plug gapping tool choices and bring you through the steps to perform a successful gapping job.

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What Is a Spark Plug?

Spark plugs work by using a spark that ignites the mixture of fuel and air inside a combustion chamber. The spark plugs in modern vehicles are also used to contain the pressure that’s created by combustion, which is the purpose the device serves after an engine has started.

Spark plugs also divert heat away from combustion chambers.

What Is a Spark Plug Gap?

The spark plug gap is important because it prevents surges in voltage that can cause problems in combustion engines. If the voltage is surging it can cause an engine to misfire and damage internal components. Having too large of a spark plug gap can also increase the wear on spark plugs and cause an engine to not start properly or consistently.

What Should the Spark Plug Gap Be?

Most spark plugs come with the appropriate gap from the factory and most gaps are between .05 or .06 inches. Before placing new spark plugs in a vehicle we recommend checking the gap to avoid problems. That said, the spark plug gap that’s appropriate for your vehicle will vary. For example, spark plug gaps used for racing are small (.04 or .035 of an inch) because of the type and ignition, fuel grade, and cylinder head size. Additional factors like timing can also impact the spark plug size.

Problems With Un-gapped Spark Plugs

Spark plugs without the proper gap will cause problems for engines; this is especially true for high-performance vehicles.

Without the proper gap, spark plugs can cause problems like:

These are only a few of the issues that spark plugs with the wrong gap space can have. Having a bad gap can also result in an engine failing to start and general performance problems.

How To Find the Spark Plug Gap

Finding the spark plug gap size is important if you plan on altering the spark plug gap. There are many ways to find the spark plug gap and you can even use some household items like coins to find the measurement of the spark plug gap.

We’ll take you through a few things you can use to find the gap size of a spark plug without a specific spark plug gap too.

Using Feeler Gauge 

Feeler gauges are one of the best tools to use for spark plug gaps. There are some feeler gauges designed for spark plugs but many people have feeler gauges laying around the house for other purposes.

A feeler gauge is a hand-held tool with many pieces that fan out from the handle. Feeler gauges are used to measure small gaps between two items, which makes them useful for the small gaps found on spark plugs. You can find feeler gauges at most hardware stores but for spark plugs make sure the tool can measure things that are less than half an inch.

It’s also easy to use a feeler gauge. To measure the spark plug gap with a feeler gauge, follow the steps below:

  1. Remove spark plugs from the engine or the box.
  2. If the spark plugs are from an engine, make sure you clean them to remove dust and debris that can give you an inaccurate measurement.
  3. Insert the feeler gauge into the space between the center electrode and the ground strap of the spark plug.
  4. Repeat step 3 with different size feelers until the feeler touches the center electrode and ground strap; this tells you the spark plug gap.
  5. Use a gap tool to alter the spark plug gap if needed.

While there are feeler gauges for general applications, you can get specific feeler gauges for spark plugs. Feeler gauges for spark plugs are circular gauges that you can rotate within the spark plug gap until it touches the center electrode and ground strap.

Using a Coin

If you don’t have a feeler gauge there’s no need to panic. You can use a coin to measure the spark plug gap. Coins are a great choice because they have heights that are similar to the appropriate size for a spark plug gap when laying flat.

The best two coins to use to measure a spark plug gap are pennies and dimes. Dimes have a height of .053 inches and pennies have a height of .06. You can also use quarters as a reference but their height of .069 inches is too large for most spark plug gaps.

To use a coin to measure the gap of a spark plug simply insert the coin between the center electrode and the ground strap of a spark plug.

For most vehicles, the spark plug gap should be between .05 and .06, so using pennies and dimes gives you a good idea of whether or not your spark plug gap is correct. One example is that the spark plugs in a Ford Mustang (2011-current) are gapped to .053 inches. In this example, using a dime to measure the spark plug gap would give you an accurate measurement.

How to Gap Spark Plugs Without Tool 

There are specific gap tools for spark plugs and we recommend using one if you plan on altering the gap. However, you don’t need a spark plug gap tool to adjust the gap on a spark plug.

There are several tools you can use as long as it’s strong enough to bend the center electrode without breaking it. The goal is to tap it and make small adjustments instead of bending it out of place. Bending the spark plug center electrode with too much pressure can damage the electrode and the spark plug.

Tools You Can Use to Adjust the Gap on a Spark Plug 

There are many tools you can use to adjust the gap size on spark plugs. Ultimately, you want to use a tool or item that has a hard surface. Several things found in most homes can be used to adjust the gap on spark plugs. These items are listed below:

You can use any of these items to adjust the gap but we recommend using items made of metal that have smooth surfaces to prevent damaging the electrode.

How to Adjust the Gap on a Spark Plug 

Adjusting the gap on a spark plug is not challenging and can be done in a few minutes. When it comes to adjusting the gap on a spark plug the difficulty comes from getting the measurement precise.

A precise spark plug gap is important because if the gap is off by even .01 of an inch, engine problems can occur.

Below are the steps to adjust the gap on a spark plug:

  1. Locate the spark plugs within the engine.
  2. Use a socket wrench or torque wrench to remove the spark plugs from the engine.
  3. Check your vehicle’s owner’s manual for the appropriate spark plug gap (this can also be found online).
  4. Clean the spark plugs to avoid debris or dust giving you the wrong measurement.
  5. Insert a coin or feeler gauge between the center electrode and the ground electrode.
  6. If the coin or feeler gauge does not touch both sides of the spark plug, use a screwdriver or another small tool to tap the ground electrode until it touches the measuring tool.
  7. On the other hand, if the measuring tool does not fit between the center electrode and ground electrode, use pliers or a coin to gently bend the ground electrode upwards.
  8. Keep checking the gap size and altering the ground electrode until the spark plug gap is within the recommended specifications.

You can use these steps for most spark plug gap adjustments but you should avoid making adjustments to iridium spark plugs because any amount of pressure on the ground electrode can damage them. We also recommend against altering platinum spark plugs without help from a technician. 

Spark Plug Made Simple 

A spark plug gap seems like something small (literally) but it can cause big problems for your engine if it’s not perfect. The wrong spark plug gap will cause your engine to misfire, perform poorly, and even damage the starter and engine components.

While we recommend using a gap tool or taking your vehicle to a professional technician, you can always gap a spark plug with a few household items like a coin or a set of pliers. Always make sure you take perfect measurements before adjusting the gap between the spark plug electrode and the ground strap.

Jed Lehman

Jed Lehman is a born gearhead who has been working on cars since he could crawl. He inherited his love for auto from his grandfather who owned a maintenance shop in Carlsbad, California. Jed is the driver behind Gearshift, and started this site to provide straightforward, helpful automobile information. From maintenance tips to product reviews, you can find it all here.