How to Check a Spark Plug Gap
All gasoline engines use a spark plug. The spark plug conducts a high-voltage electrical signal from a control device. This high-voltage electrical spark ignites the fuel inside the engine. The gap on the spark plug is the distance between the center electrode and the exterior engine ground point. The ground point on a spark plug resembles the letter J, with the lower part of the J connected to the spark plug body. The upper, straight end of the ground point is a set distance from the center electrode. This distance is the "gap" of the spark plug.
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Instructions
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Hold the spark plug in one hand. Place it so the gap area is facing upward and you can clearly see both the center electrode and the ground point, or the J, on the plug.
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Consult the engine specifications for the correct gap setting of the spark plug. It may read 0.025 inches or just 0.025.
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Find the same marking on the spark plug gap tool. There will be various gap settings on the end of the spark plug gap tool.
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Insert the correct gap setting on the gap tool between the center electrode and the ground point of the spark plug. Gently fit the tool between the two points. You may have to lightly force the tool between them if the gap is too small.
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Press the flat edge of the ground point against a firm surface if the gap is too loose in order to close the distance between the electrode and the ground point. Check the gap again with the gap tool. It must be a snug fit. Always double-check the gap setting on every spark plug before you install it into any engine.
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Tips & Warnings
Set the gap on all spark plugs even if you are simply inspecting the engine for routine maintenance. Often, an ill-running engine can be cured by resetting the gap on the spark plug.
Follow the manufacturer's spark plug gap specifications to the letter. Failure to do so will result in the engine running improperly and may cause premature damage to the engine.
