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How to Gap Spark Plugs with a Gapping Tool

4 min read
The tips of two models of NGK Iridium spark plugs

This guide will show you how to gap your spark plugs with a spark plug gapping tool.

If you’re not sure why you would want to gap your spark plugs, scroll to the bottom of this article

Spark Plug Gapping Tools

To gap your spark plugs properly you will need a

  • spark plug removal tool,
  • needle nose pliers,
  • a loop spanner
  • your spark plug measuring & adjusting tool.

In this video we use a Champion branded item.

Gapping the spark plugs for a Ford Focus 1.6 Zetec SE

Spark Plug Removal

First step is to get to your spark plugs. Remove anything that is blocking access eg spark plug cover.

Remove your ignition coil or ignition lead of the first cylinder.

Get your spark plug removal tool on the first spark plug and unscrew it, counter clockwise. If it is tight put the spanner onto your removal tool to give yourself more leverage.

With the spark plug out, check it’s condition ie that nothing is obviously wrong with it.

Measuring Gap and Adjusting

Assuming everything is okay, it’s time to measure the spark plug gap. Does your spark plug actually need to be adjusted?


Reading Spark PlugsThe colour of spark plug tip will tell you a lot about your engine’s fuel mixture ie lean, good or rich. The spark plug tip will also tell you if the engine has major issues eg you may have water or oil in the end of your spark plug.


If your spark plug gap needs to be adjusted, 99.999% it will be because the gap is too big. Now you know your current spark plug gap and the correct spark plug gap you have an idea of how much you need to adjust the conductor of the spark plug by.


How to find the correct gap – We recommend checking the spark plug manufacturers website and their “part finder”. This will tell you the product code of the correct spark plugs, the hex size (so you now which spark plug removal tool you need), the general dimensions of the plug and the spark plug gap.


Put the teeth of the tool around the conductor and bend the conductor gently. Then check the gap. Repeat this process of measuring and adjusting until you get the spark plug gap you need.

Reinstalling the Spark Plug

Put the spark plug back in the engine. Lower the spark plug into the hole with the needle nose pliers, no need to drop the plug into place an risk damaging it.


Top Tip

With the plug in the hole put your removal tool back on the plug and put downward pressure and start turning your spark plug counter clockwise, the direction you turned it to remove it.


What you are waiting for is a click as the threads of the spark plug and cylinder head match up. We do this to reduce the chance of cross threading the spark plug.

As soon as you feel the click, tighten up the spark plug. Feel the spark plug as you tighten, don’t let your self cross thread. the spark plug should go in with minimum resistance until it reaches the bottom of the thread. When you feel the spark plug stop against the cylinder head, I give it another 1/8th to 1/4 quarter of a turn. There is no need to put spark plugs in super tight.

Replace the coil pack or spark plug lead and repeat the process for the other spark plugs.


Why would you want to gap your spark plugs?

The only reason is to ensure your spark plugs work properly and this usually means having the factory recommended spark gap. The car manufacturer has designed the ignition system and combustion chamber to work at a specific gap.

Modified Engines

If you are running higher compression, the engine is modified and/or you are running increased boost pressure you may find your spark is “blowing out”. Denser air/fuel mixtures makes it harder for the spark to jump the gap.

If you are experience misfires reducing the spark gap will help the ignition system because a smaller gap makes it easier for the spark to jump. Adjust down in small steps until you find the gap that works. Use the biggest gap you can get away with but no bigger than the factory spec gap.

Off the shelf spark plugs

Spark plugs usually come pre-gapped, this means you do not need to adjust the gap before you fit them in your engine. For example NGK part numbers without a “-11” at the end will be gapped to 0.8mm.

With the “-11” means the spark plugs have a 1.1mm gap.

It’s possible that your local auto parts store only has, for example, BKR8EIX in stock but the factory plug is BKR8EIX-11

In this case you can buy the EIX and re-gap them at home. You do not have to leave the store empty handed just because the exact spark plugs aren’t in stock. If the only difference, is the plugs they have don’t have the right gap, you can adjust it.

These are the three basic reasons we think you would need to adjust your spark gap.

To maintain factory tolerance, to help an ignition system at the limit, the auto part store had the correct plugs but the gap was not correct.


This page was last modified Mar 7, 2021 @ 1:06 am

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