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What You Need to Know to Adjust a Spark Plug Gap

Updated: Dec. 12, 2018

Be sure to set and adjust the spark plug gap for your particular engine!

spark-plug-gapFamily Handyman
Good engine performance requires the proper spark plug gap. You can measure and adjust the gap in minutes to fit the specifications of your engine.

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How to set spark plug gap

Photo 1: Check the gap with a gap gauge

Find the “gapping wire” that matches the recommended gap. Then slide it between the center and side electrodes. When the spark plug gap is correct, the gauge should drag slightly going in and out. If the spark plug gap is too large or the wire won’t fit, adjust the side electrode. You can also use a gap gauge like this one for this step.

Photo 2: Bend the side electrode

Hook the side electrode with the gauge’s bending arm. Then pivot the arm in or out in small increments to open or close the gap. Recheck with the gauge until you get a snug fit.

Spark plugs don’t come gapped for your particular engine. For the best performance, you must gap the plug to the engine manufacturer’s specs. If you’re buying a plug for a small engine, ask the parts store to look up the gap size info for you. If the plugs are for your vehicle, find the info in the owner’s manual. Then adjust the spark plug gap as shown with a spark plug gapper.

Required Tools for this Spark Plug Gap Project

You’ll need a spark plug socket and a gap gauge.