Gapping Your Spark Plugs
*EASY*
New spark plugs are not ready to use, even out of the box. Replacement plugs must be "gapped" before being used. In other words, the distance between the side electrode and center electrode must be measured and adjusted to conform to your car manufacturer's recommendation. Specific gaps vary from about 0.030" to about 0.060". If the gap is given as a range, say 0.045 – 0.049", set it at the average, or 0.047". It is important to set the gap properly. If the gap is too small, the spark will also be too small; performance will suffer.
SPARK PLUG
Courtesy of Car Care Council
To gap the spark plugs, follow this procedure completely for each plug:
- Use a wire feeler gauge to measure the existing distance between the center electrode and side electrode. Try to slide various sized metal wires through the gap. When the wire slides through snugly, the gap has been identified; it is the wire's thickness. If the gap is at the vehicle manufacturer's specification, no adjustment is necessary.
- If the gap is too wide, use the bending tab on the electrode adjuster to bend the side (ground) electrode downward. Do not attempt to bend the center electrode; this will crack the insulator and ruin the plug. The side electrode metal is relatively soft so tremendous pressure is not required to bend the electrode. Besides, the adjustment distances are minuscule.
- If the gap is too small, use the electrode adjuster to bend the side electrode upward. Repeat the bending and measuring process until all spark plugs are gapped within specification. It is better to repeatedly bend the electrode in small increments in the same direction than it is to bend it back and forth in large increments toward the same desired gap. A weakened side electrode could eventually break off inside the engine and cause extensive damage to the piston, cylinder wall, or valves.
- Repeat the steps above for each spark plug; never assume that new spark plugs are correctly gapped. It may be desirable to have an extra spark plug available in case one breaks during adjustment.
- Install the sparks plugs and connect the wires as outlined in Inspecting Your Spark Plugs.
