Spark plug gap — the distance between the center electrode and the ground electrode — has a significant effect on engine performance. Too wide and the ignition coil can't jump the gap reliably. Too narrow and the spark is weak. Here's everything you need to know.
What Is the Correct Gap?
Every engine has a specified gap (typically 0.028" to 0.060", or 0.7mm to 1.5mm). Find yours in the owner's manual or on the vehicle emission sticker under the hood. The correct gap for your engine is non-negotiable.
Tools You Need
- Wire gap gauge: Best for precise measurement on smaller gaps
- Coin-type gap gauge: Works for most standard applications
- Feeler gauge set: Most precise option for iridium plugs
How to Gap a Spark Plug
- Measure the existing gap with your tool
- If too wide: carefully bend the ground electrode inward
- If too narrow: use the gap tool's notch to pry the ground electrode outward slightly
- Re-measure and verify
Iridium Plugs: Handle With Care
Many pre-gapped iridium plugs from NGK and Champion come correctly gapped from the factory. Verify before installing, but be very careful bending the ground electrode — the ultra-fine iridium center electrode is fragile and easily damaged by contact with gapping tools.
Never Adjust the Center Electrode
Only bend the ground (side) electrode when adjusting gap. The center electrode on any plug — especially iridium — should never be touched.
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