Do Spark Plugs Always Have to Be Gapped? Not always. In the past, it was necessary to gap spark plugs, but today spark plugs are usually pre-gapped. It is advisable to double check that the gap is correctly set to the vehicle’s recommended setting when installing spark plugs.

For most racing applications, you usually want the plug gap to be between 0.020 and 0.040 of an inch. Most engine builders seem to settle around 0.035 of an inch. Factors such as the type of ignition you run, cylinder heads, fuel and even timing can affect how much gap will work best for you.

Spark plugs in automobiles generally have a gap between 0.6 and 1.8 mm (0.024 and 0.071 in). The gap may require adjustment from the out-of-the-box gap. A spark plug gap gauge is a disc with a sloping edge, or with round wires of precise diameters, and is used to measure the gap.

This spark plug comes pre-gapped from the factory. If you want to check the gap the spec is :6mm (. 024″) – .

Excessive spark plug gap results when the voltage has too far to travel. Excessive plug gap also results in cylinder misfiring, a possible no-start condition, wet, black or fouled plugs, engine hesitation and rough idle. Excessive spark plug gap also happens as result of normal electrode wear and age.

In order for a spark plug to work as it should, the gap between the ground and centre electrodes needs to be perfectly calibrated. By adjusting this distance you are sad to be ‘gapping your spark plugs’.

Spark plugs that are gapped incorrectly can cause an engine to miss, or run erratically, especially during idle. The incorrect spark plug gaps can cause uneven firing of individual spark plugs and delay engine combustion; both of which can cause an engine to miss or idle erratically.

028″ which is roughly 0.7mm. Be careful gapping iridium plugs.

The Spark-Plug Gap If the gap is too small, the spark will likely be too weak and cause the engine to run poorly or with poor efficiency. A spark-plug gap gauge both measures and adjusts the gap and is inexpensive and simple to use.

A list of some of the most common symptoms of incorrectly gapped spark plugs is laid out below.

1. Rough Engine Idle. An engine that has a rough, irregular engine idle is often due to spark plugs that are incorrectly gapped.
2. Engine Hesitation.
3. Engine Missing.
4. Poor Engine Performance.
5. Engine Knocking.

Excessive changing of the spark plug gap setting will result in weakening of the spark plug ground electrode and can lead to breakage. Also, the spark plug gap should never exceed .055″ unless pre-set by the manufacturer. Most Brisk and other manufacturer sparkplugs are preset to around 0.75mm – 0.8mm.

The spark plug gap adjustment should not be changed more than 3 times and should not exceed .008″ in either direction. Excessive changing of the spark plug gap setting will result in weakening of the spark plug ground electrode and can lead to breakage.

Some applications such as ProMod turbo cars using M1 fuel frequently run a spark plug gap as small as .012″, even though they are equipped with some of the highest output ignition systems providing in excess of 60,000 Volts high current and high mJ power output.

It is not uncommon to gain as much as 20 Hp just by replacing used spark plugs. Used spark plugs are hard to fire as the gaps are worn out, and insulation properties of the ceramic is compromised by solid combustion deposits and old fuel saturation.