How to Gap Iridium Spark Plugs

by Brenton Shields

Spark plugs are an essential component of a car's operation. Like the name implies, spark plugs literally provide a spark that ignites the fuel in your car's combustion chamber, moving the pistons up and down and giving the engine its power. While iridium spark plugs, which are the most common type, are relatively easy to remove and install, they must sometimes be properly gapped before installation, which means altering the distance between the ground electrode and the center electrode to provide a longer or shorter spark. This is a simple, yet delicate, task that requires concentration and care.


Identify the center electrode and ground electrode. The ground electrode will be the copper-colored electrode curving over the top of the spark plug. The center electrode will be the silver-colored electrode sticking directly out the top of the spark plug and will end directly underneath the curvature of the ground electrode. You must take great care to never touch the center electrode or the porcelain that encases it.


Determine how wide the gap must be. Each make and model of car will have a different proper gap, so consult your owner's manual or contact your dealer.


Take the needle nose pliers and gently pull the ground electrode up away from the center electrode by a few millimeters.


Measure the gap between the center electrode and the curvature of the ground electrode. If it is the proper distance, you're finished and the spark plug has been gapped. If not, adjust the gap accordingly. To decrease the size of the gap, gently press down on the top of the ground electrode, pushing it back into the plug.


  • check Ask for pre-gapped spark plugs from your local auto parts store. Chances are, your spark plugs are already pre-gapped according to your specific make and model, but always make sure. Even if your spark plugs are pre-gapped, it's always a good idea to measure the gap just to make sure, as the gap may have been altered during handling.
  • check Special gapping tools are often available for purchase from auto parts stores. These essentially look like rulers with niches cut into the top of one side. These are useful for getting an exact measurement but needle nose pliers are easier to use.

Items you will need

About the Author

Brenton Shields began writing professionally in 2009. His work includes film reviews that appear for the online magazine Los Angeles Chronicle. He received a Bachelor of Science in social science and history from Radford University.

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