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Do New Spark Plugs Have to Be Gapped?

by Justin Cupler

Today's internal combustion engines are continuously becoming more advanced and producing better horsepower-per-liter ratios. All of this advancement is occurring thanks to the use of a component that Edmond Berger invented in 1839: the spark plug. The spark plug takes an electrical current and forces it to jump a small gap, creating a spark that lasts only milliseconds. This gap is often a deciding factor in whether the car runs well or not at all.

Little Tolerance

Automakers build their cars to use spark plugs with gaps measured in thousandths of an inch. The gap on most mass-produced spark plugs ranges from 0.035 and 0.049 inches, with a tolerance of plus or minus 0.003 inches.

Checking New Spark Plug Gaps

Nearly all companies that mass-produce spark plugs pre-gap the spark plugs before they ship them out. Shipping and handling, however, may cause the plugs to move around, resulting in changes in the gap size. For this reason, when replacing the spark plugs in your car, you must check the gap in the plug prior to installing it.

Adjusting New Spark Plug Gaps

If the gap on a spark plug is not within the manufacturer's specified range, do not install this plug. If the spark plug is a standard copper plug, you can readjust the gap. If the spark plug is iridium- or platinum-tipped, refer to the spark plug manufacturer's recommendation on adjustment. Many state not to readjust the gap.

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