Spark Plug


Regapping Spark Plugs

Both new and used spark plugs should have their air gaps set to manufacturer's specifications.

Use an approved toolnot only to measure the gap but also to bend the side electrode to make the adjustment. Do not try to reduce a plug's air gap by tapping the side electrode on a bench. Never attempt to set a wide-gap, electronic-ignition-type plug to a small gap specification. Likewise, never attempt to set a small-gap, breaker-point-ignition type plug to the wide gap necessary for electronic ignitions. In either case, damage to the electrodes results. Never try to bend the center electrode to adjust the air gap. Doing so cracks the insulation.

Most late-model engines are equipped with platinum-tip spark plugs. Extra care must be taken when setting the gap on these plugs. A wire gauge is recommended by many manufacturers for checking and adjusting spark plug gap. However, the use of more delicate spark plugs has led many manufacturers to recommend the use of a tapered gauge.

Using a tapered gauge to check spark plug gap. Courtesy of DaimlerChrysler Corporation.

If the spark plugs have more than one ground or side electrode. The gaps of these plugs cannot be adjusted with conventional tools, and most manufacturers recommend that the gap be left alone.

But setting the gap is not the only thing you have to do when regapping your spark plugs. You also have to torque the spark plugs into the cylinder heads. If the spark plugs are not properly torqued into the cylinder heads, the threads of the spark plug may not make good contact and the circuit may offer resistance. Always tighten spark plugs to their specified torque. Many of today's engines have aluminum cylinder heads. Not only do these heads require different torque specifications than iron heads, they also require extra care when installing the plugs. Make sure the threads of the plugs match the threads of the spark plug bores. Take extra care not to cross-thread them. Repairing damaged threads in a cylinder head can be a costly and time-consuming job.

Most manufacturers recommend the use of an anti-seize compound on spark plug threads. This compound must be applied in the correct amount and at the correct place.

Proper placement of antiseize compound on the threads of a spark plug. Courtesy of DaimlerChrysler Corporation.

Too little compound will cause gaps in the contact between the spark plug threads and the spark plug bores. Too much may allow the spark to jump to a buildup rather than to the spark plug electrode.