When replacing spark plugs, ensuring that the plugs have the proper gap is critical to engine performance. The gap is the distance between the center and side electrodes, set so arcing occurs at the proper voltage that ignites the fuel and generates the combustion that makes the engine run.
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.
The distance between the tip of the spark plug and the central electrode is called the “spark plug gap” and is a key factor in the function of a spark plug. Spark plug gaps for car engines are typically 0.6 to 1.8 mm (0.024 to 0.071 in).
Modern engines (using solid-state ignition systems and electronic fuel injection) typically use larger gaps than older engines that use breaker point distributors and carburetors.
Smaller plug gap sizes usually are more reliable at producing a spark, however the spark may be too weak to ignite the fuel-air mixture. A larger plug gap size will produce a stronger spark, however the spark might not always be produced (such as at high RPM).
Gap adjustment is not recommended for iridium and platinum spark plugs, because there is a risk of damaging a metal disk welded to the electrode.
Consult the owner’s manual to find the recommended setting for the vehicle you’re working on.
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How To Gap Spark Plugs?
#1. Measure the Gap.
The first step is to figure out the size of the gap that your vehicle requires. My vehicle requires a 0.054″ spark gap.
We will now measure the gap on one of the new spark plugs using our spark plug gap measuring tool. As you can see this gap is about .002″ larger than what we need.
#2. Adjust the Gap.
In order to adjust the gap we will use our spark plug gap adjustment tool. The tool uses leverage in order to increase or decrease the size of the gap. Slightly adjusting the gap takes very little force.
In this case we will gently pull the lever toward the opposite side of the spark plugs electrode. Be careful not to contact the ceramic or metal core in the center of the plug as this might damage the ceramic.
If the ceramic breaks you will need to throw the plug away and purchase a new one.
#3. Re-measure the Gap.
Once you’ve completed the adjustment it’s time to re-measure the gap. This gap adjustment was successful. We now have a gap of .054″ If you don’t get the proper gap on the first adjustment, simply repeat the process until the desired result is achieved.
Consequences of Incorrect Spark Plug Gap
If the spark plug gap is incorrectly set, it can lead to engine issues. The customer may experience loss of power, misfires, spark plug fouling, increased plug wear, or poor gas mileage.
Too small of a gap may give too weak of a spark to complete the combustion process within the engine; too wide of a gap can lead to the spark plug not firing correctly, causing misfires at high speeds.
Types of Spark Plug Gap Tools
Whether you’re looking to maximize the performance of your vehicle or just want to double check that the setting is right, using a spark plug gap tool is vital.
#1. Feeler Gauge.
Featuring several metal blades or wires in different thicknesses, a feeler gauge looks like a pocket knife. Each blade or wire is a specific thickness marked in thousandths of an inch (imperial) or millimeters (metric). With a wide variety of blades or wires, you’ll be able to measure almost any gap.
Ideal for use with iridium spark plugs and other plugs containing precious metals, feeler gauges are more accurate than other types. A drawback is the fact that you’ll need a pair of pliers to bend the spark plug electrode since the blades will become deformed if you try using them to adjust the plug.
#2. Coin Style Spark Plug Gauge.
Named for its coin-like shape, a coin-style spark plug gauge features measurements around the edge. The gauge’s outer edge is thin and as you move around the gauge, it gets thicker. This type of gauge is also called a ramp style gauge.
Economical, you can bend the spark plug electrode with this tool but accuracy can be an issue due to the gradual slope of the edge. Good for traditional copper spark plugs, it shouldn’t be used with iridium spark plugs. Using a coin gauge can damage the precious metals in this type of spark plug.
#3. Wire Loop Spark Plug Gauge.
The wire loop style is also shaped like a coin but it has several wire loops of different thicknesses protruding from the edge. As accurate as a feeler gauge, it has a hook to bend the spark plug electrode. A drawback is the limited number of loops, which can make it ineffective for odd gap sizes.