How to Close Spark Plug Gap (Step-by-Step)

Have you been experiencing misfire, reduction of power, or poor mileage on your vehicle? These problems might be due to an underlying cause in the spark plug. Your spark plug has not been gapped properly.

Don’t worry. In this article, I will explain in the detail the function of spark plugs, the significance of spark plug gap, and the step-wise procedure of how you can close the spark plug gap.

What is a Spark Plug and its Function?

Spark Plug is the most significant component of a gasoline internal combustion engine. As the air-fuel mixture enters the combustion chamber, the spark plug initiates combustion and starts the engine.

Construction and Working:

The spark plug is composed of three distinct layers. The outermost layer is a threaded metal shell that reinforces the structure. The side electrode is attached to this shell on one end and is grounded due to its connection to the metal case.

Within the metal shell lies a porcelain layer that acts like an insulating surface for the primary electrode. Then, there is a primary electrode, inside the porcelain shell, through which the current runs.

One electrode end of the spark plug is connected to a high voltage source, while the other electrode end goes into the combustion chamber. The input current creates a potential difference (voltage drop) between two electrodes.

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The gas mixture between them functions as an insulator, preventing electricity from flowing past the tip of the center electrode. But when the voltage rises, the gap gases get ionized.

The ionized gases behave as conductors, allowing current to flow over the insulating gap. After crossing the dielectric strength, electrons start rushing. This abrupt flow of electrons raises the heat in that region, generating a tiny explosion, termed a spark.

Types of Spark Plug:

Now, based on the material of the electrodes, there are multiple types of spark plugs. Namely, copper spark plugs, iridium spark plugs, single platinum spark plugs, silver spark plugs, etc. Copper spark plugs are the most common due to their cheapest price. But they have a short lifespan. Iridium and Platinum spark plug last longer but are quite expensive.

Based on the operating temperatures of the tip, there are two types of spark plugs, hot and cold spark plugs. Hot spark plugs operate in high-temperature conditions and are ideal for normal vehicles. In high-performance engines which already are very hot, hot spark plugs may cause pre-ignition. So, cold spark plugs are used.

Significance of an Accurate Spark Plug Gap

The distance between the ground/side electrode and central electrode of a spark plug is termed the spark plug gap, and adjusting this distance is known as spark plug gapping.

Accurate gapping of a spark plug is critical to engine performance. If the gap is too small, the spark plugs will produce an ineffective or weak spark, resulting in lower fuel efficiency and engine performance.

On the hand, if the plug gap is larger, sparks will not reliably ‘jump’ across the space between the ground electrode and the center electrode. This may result in a harsh idle engine, lower fuel economy, and in the worst scenario, engine failure.

Factors Affecting the Spark Plug Gap

Since different engines have varying operating environments. The design, size, and form of the spark plug are determined by considerations such as fuel type, combustion pressure, and engine load.

  1. Fuel Type and Concentration:

If you use a fuel that has higher alcohol content. Then it requires less air to fuel ratio and a short spark plug gap.

  1. Combustion Chamber Pressure (at spark discharge)

Engines with a high compression ratio need a higher voltage to spark.

  1. Engine Load and Application

When the load on the engine is increased, the cylinder pressure increases, and more air is aspirated into the engine. In that case, it is hard to generate the spark.

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How to Close Spark Plug Gap (Step-by-Step)

Now, since you have known the function and purpose of the spark plug. It’s time to tell you how you can set the correct spark plug gap.

You can set up an accurate spark plug gap by following these steps.

Step # 1: Remove and Clean the Spark Plug

Remove the spark plug if it is installed in the engine and clean it with a cloth. If it is new, then it will already be clean. In that case, move directly to the next step.

Step # 2: Measure the Gap

Now, you need to measure the gap with the feeler gauge. Place the feeler gauge blade of recommended thickness in between the electrodes. I cannot mention the exact gap you need to set, because the gap setting varies from vehicle to vehicle. It is somewhere between 0.028” to 0.060”. To get the accurate value, you need to check the information in your owner’s manual.

Keep in mind that modified engines require reduced gap settings to compensate for the increased power output. In general, the greater the power, the narrower the gap.

If the feeler gauge is unable to fit within the required gap size, the plug gap must be widened. If the feeler gauge or gap gauge (with the appropriate size) goes through the gap without coming into contact with an electrode, the gap is too large and should be decreased.

Step # 3: Adjust the Gap

To adjust this gap, you need a gap tool. Bend the ground electrode gently to broaden or close the gap. Spark plugs are very delicate, so they won’t take much pressure. Never bend the electrode more than 0.02”.

Step # 4: Recheck the Gap

Once you have adjusted the gap using the gap tool. Recheck the gap with the help of a feeler gauge. If the gap still needs adjustment, you need to repeat Step 4 until the recommended gap setting is achieved.

How to Measure Spark Plug Gap with Feeler Gauge?

One of the common tools to measure the spark plug gap is a feeler gauge. It is a gap tool made up of well-calibrated metal strips/blades of varied thicknesses. Feeler gauge resembles a pocket knife and is an extremely useful and affordable gapper. Each blade has a specific thickness marked in millimeters or inches

To measure the gap with the feeler gauge, you have to place each blade turn by turn into the spark plug. The blade that fits inside the gap tells you the existing gap. Or you can place the blade of recommended thickness in between the electrodes of the plug. If the blade doesn’t fit, it means the gap needs to be widened. And if the blade is loose inside the electrodes, the gap needs to be narrowed.

How Can You Improve Spark Plug Health?

To improve the health of the spark plug, choose the right type of spark, regularly examine the gap of the spark plug, and clean off the electrodes and mounting area.

  • Choose the appropriate Plug: Before installing a spark plug, you must select the most suitable type of plug. For instance, utilizing a cold spark plug in a low-performance engine, the heat will be dissipated too quickly, resulting in a delayed spark release. Similarly, using a hot spark plug in a high-performance engine may result in the tip melting off.
  • Gap the Spark Plug: Examine the gap between the electrodes of the spark regularly and make necessary adjustments. This improves engines efficiency and the health of the plug.
  • Regularly Clean the Electrodes: Remove the spark plug and soak it in a thinner liquid like petrol, or diesel. Remove the deposits from the electrodes using sandpaper or brush. In addition, clean off the area where the plug is mounted because the dirt and debris can cause the spark plug to be misaligned.

What Happens if the Spark Plug is not Gapped Properly?

If the spark plug gap is set wrong, engine problems can occur. The driver may notice a reduction of power, misfires, spark plug fouling, increased wear on the plugs, or poor gas mileage. A gap that is too narrow will result in an insufficient spark to complete the combustion process within the engine; a distance that is too large will result in the spark plug not igniting properly, resulting in misfires at high speeds.

I hope by now you would have understood the function of a spark plug and the significance of the spark plug gap. And I believe that you can close the spark plug by yourselves by following the guidelines mentioned in this article.