How To Gap Spark Plugs in a Car

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As you likely know, changing your spark plugs is an important part of maintaining your vehicle. Whether you are performing routine maintenance or a tune-up, you may have looked up the right plug using a free VIN lookup and gotten all your tools ready. As you get ready to put the new plugs in, you realize you need to gap them. What does that mean? How do you do it?

What Is Gapping?

The gap on your spark plugs is the space between the straight and curved electrodes. This is where a lot of the “magic” of the spark plug happens. The distance of that hap matters a lot to how your vehicle operates.

Your spark plug gap needs to be configured to match the voltage and amperage generated by the ignition coil. Fortunately, the process of gapping is fairly simple: you are merely changing the distance between the two electrodes.

Nonetheless, it is essential to get this right. Having an improper gap could cause premature wear, engine stress or even misfires.

Pre-Gapped Plugs

Many spark plugs are sold as being “pre-gapped.” This is perhaps a slight overstatement. The issue is that the plugs need to be gapped to match your engine. So, while the spark plug manufacturer may have pre-gapped the spark plug to be close to the needs of an average engine, there is no way to be sure it is configured for your engine.

Therefore, even if you have a pre-gapped spark plug, you should check it with a gauge. You may need to make a small adjustment.
Using a Feeler or Wire-Type Gauge

If you have a newer spark plug, especially one using a rare metal such as iridium, make sure you use a feeler or wire-type gauge. This is a more accurate way of measuring spark plugs than a coin-type gauge. The more advanced spark plugs need to be more carefully gapped.

Find the correct wire to fit the gap in the current spark plug electrodes. Slide the wire until it catches on the electrodes as it passes through. This should give you a precise measurement of the current gap

For the new electrode, line up the same place on the wire. Use this is as a guide to adjust your electrode gap. You can make adjustments either by gently widening the distance with the feeler gauge or by lightly tapping the curved electrode to narrow the gap.

Using a Coin-Type Tool

The process of using a coin-type tool is similar. These are more widely available and very inexpensive. However, they are a little less accurate. Nonetheless, they work perfectly for copper/nickel spark plugs.

Insert the coin gauge into the spark plug. Find the measurement that matches the gap using the ramp on the coin. If necessary, widen the gap using the hole in the coin. Alternatively, gently tap the electrode to narrow the gap.

Get Started

Although gapping your spark plugs may sound intimidating, it is very easy once you have a little practice. Just make sure you have the right tools on hand for your type of spark plug.

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