How to Create a Spark Gap

The spark gap is the space between the central electrode and the lateral electrode.

Spark plugs ignite the fuel and air mixture in an engine's combustion chamber. A high-voltage electrical current is sent through the spark plug and jumps the gap between the side electrode, or arm, of the spark plug to the center insulated electrode. The spark plug gap size determines the efficiency and reliability of the spark. Shorter gaps require less voltage to reliably spark, but provide a smaller spark that may not fully ignite the mixture of fuel and air. Larger gaps provide longer sparks for a more efficient burn, but require sufficient voltage or misfires will occur.

Things You'll Need

• Gap tool
• Flat-head screwdriver

Instructions

1. Remove the spark plug from the engine or, if new, the box.

2. Slide thinnest part of the the gap tool between the spark plug's central electrode, commonly referred to as the "post," and the lateral electrode, commonly referred to as the "arm." The space between the post and arm is the "gap."

3. Increase the size of the tool inserted in the gap until the tool is snug. If using a disk-type gap tool, read the side of the disk to determine the gap measurement. If using a key tool, read the stamping on the key to determine the thickness of the blade inserted in the gap. The distance will be measured in a portion of an inch, such as "0.032 inches."

4. Determine the correct gap size for your engine size. The gap size should be available in the owner's manual. If the owner's manual is unavailable, contact the engine manufacturer or an automotive parts store.

5. Adjust the arm of the spark plug away from the center post if the gap size needs to be increased. To decrease the size, push the arm of the spark plug toward the center post. Gentle pressure with a flat-head screwdriver will lift the arm increasing the gap distance. Push the spark plug, arm downward, against a flat surface to close the gap distance.

6. Re-measure the gap to ensure the adjustment was adequate. Re-adjust if necessary.

Tips & Warnings

• Optimal gap sizes depend on the engine type and application. The manufactured gap size may not be the recommended size for your engine application. Double check your engine's recommended gap size. Many spark plugs models may be installed in different engines.

• Gap tools are available as disks, a ring of flat blades or as flat pieces of material that slide between the central electrode and the lateral electrode. Regardless of the type, the gap tool will measure the distance between the electrodes.

References

• Custom-car.us: Spark Plug Gap
• NGK Spark Plugs: Gapping