Do Spark Plug Gaps Have To Be Exact?

do spark plug gaps have to be exact

Spark plugs are responsible for igniting the air/fuel mixture. In other words, an engine with bad spark plugs won’t work. These components use a spark that jumps between two electrodes as the air/fuel mixture enters the cylinders.

The spark plugs sit at the top of the cylinder. They use the vehicle’s electrical system to combust the air/fuel mixture. Some people question the relevance of the spark plug gap. Others believe that a gap of the wrong width can attract disastrous consequences. To get a better understanding of the influence of the spark plug gap, you should keep the following in mind:

What Is The Purpose Of The Spark Plug Gap In An Engine?

The gap is that empty space you see between the center and ground electrodes. The gap matters because the spark jumps between the two electrodes. Therefore, the gap can affect a spark plug’s ability to ignite the air/fuel mixture.

The manufacturer determines the gap. For that reason, laypeople rarely adjust the width. However, some mechanics prefer to double-check the gap before installing the plugs for the following reasons:

  • The gap between electrodes can close when a spark plug falls to the ground.
  • The width between the electrodes can shrink during conventional repairs. The mechanic may apply too much pressure while adjusting the gap.
  • Modifications to the engine can make adjustments to the gap necessary. NGK has given the example of modifications that introduce higher compression and forced induction, forcing the mechanic to use a smaller gap setting.
  • Some gaps shrink or grow because the spark plugs in question are counterfeit. The manufacturer used low-quality materials to make them.

How Accurate Does Spark Plug Gap Need To Be?

Spark plugs are manufactured with a specific gap. You can’t make significant changes to the width of that gap unless the spark plug falls and bends the electrodes. Even if the gap is too small for the spark plugs to fire sufficiently, this condition will only affect the vehicle’s operations when you idle because the volume of the air/fuel mixture in the combustion is low, and it is struggling to stay lit. An excessively wide gap can cause misfires under heavy loads.

A different crop of mechanics may disagree with that conclusion. This is why laypeople are encouraged to consult their local dealership or the manufacturer. The manufacturer has an intimate understanding of their car.

They will reveal the extent to which the spark plug gap matters and whether you should make the measurements as precise as possible. In the absence of trustworthy technical support, experiment with the spark plug gap and record the results.

The unit of measurement matters. Getting the gap correct to the nearest centimeter matters. However, errors measured in nanometers don’t matter.

What Happens If The Spark Plug Gap Is Not Exact?

This paper from Anggara Sukma Ardiyanta (Automotive Technology Vocational Education, Universitas Bhinneka PGRI) in Advances in Engineering Research identified two primary concerns.

If the spark plug gap is wide, it will use more voltage. If the gap is too small, arcing may not occur because of insufficient voltage. However, these issues are more likely to occur if the error is significant. A slight difference in the gap won’t matter. Additional consequences of the wrong spark plug gap include:

  • Poor fuel economy.
  • Frequent misfires.
  • Accelerated wear and tear.
  • Loss of power.

Don’t make adjustments to the gap unless you have the relevant skills and experience. After all, spark plugs use brittle materials. They can fracture if you apply excessive force.

Can A Slightly Wider Or Narrower Spark Plug Gap Affect Engine Performance?

Yes, it can. The severity of the consequences depends on the width. A slight difference will go unnoticed. The bigger the error, the more dramatic the side effects, for instance:

1). Wider Spark Plug Gap

  • A wide gap is preferable because it ignites the mixture efficiently and consistently.
  • However, a wide gap also makes it harder for the spark to jump between electrodes.
  • The spark plug requires more voltage, which strains various parts, including the coils, wires, and distributor.
  • Turbulent combustion chambers can blow out the spark.
  • Because the spark is weak, cylinder misfires may occur.

2). Narrower Spark Plug Gap

  • A narrow gap allows the spark to jump between the electrodes with greater ease.
  • Unfortunately, you may record low power because the spark cannot efficiently or fully ignite the air/fuel mixture.
  • You may find that nothing ignites when the spark plug fires because the room between the electrodes is too small to accommodate the air/fuel mixture.
  • The tailpipe emissions will increase.

The best gap is a wide one. Aim for the largest gap the engine can tolerate without blowing out the spark at peak load.

How Do I Measure And Adjust The Spark Plug Gap Correctly?

Even though spark plugs are pre-gapped, you should measure them in case they sustain damage or modifications to the engine require a different gap width. Older plugs can also become broader or narrower.

According to this paper from Aivars Birkavs and Ruslans Smigins from the Latvia University of Life Sciences and Technology, a widening gap is a sign of wear and tear. The central electrode tends to burn out as the plug ages. Use the following steps to make adjustments:

1). Specifications

What are your car’s gap specifications? You can’t measure the gap if you don’t know what the width should be. The user manual will provide this information, although it won’t help if you modify the engine.

2). Measuring Tools

Find a tool that appeals to you. The coin option is cheap. It involves pushing a coin through the gap until it stops. The blade-style feeler is more accurate. It looks like a pocket knife. Don’t proceed without cleaning the plug. The deposits that accumulate on the contact points can skew your results.

3). Gapping The Plug

Adjust the gap if the measurements don’t match the data in the manual. You can decrease or increase the gap depending on whether it’s too wide or too narrow. Use the feeler gauge for this task.

Spark plug gap measuring

If the blade cannot fit in the gap, make it wider. If the blade can run between the gaps without touching the electrodes, make it narrower.

You will bend the ground electrode inward or outward depending on your objective. But you should apply caution. Spark plugs can break. You may introduce an irreparable fracture. You can make adjustments of 0.02 fractions of an inch.

That alteration seems tiny, but it isn’t a one-off. You’re supposed to re-measure the gap afterward. If it’s still too wide or narrow, you can make another tiny adjustment. Keep going until the gap’s width matches the recommendation from the manual.

Pay attention to the vehicle’s performance afterward. Does the engine run as expected? Have you noticed frequent misfiring? Is the gas mileage poor? Are the plugs wearing out at a faster rate? You probably made a mistake with the gap. It is still too wide or narrow. 

You can make further adjustments or hire an expert. If you prefer to perform this task yourself, I suggest you disconnect the positive battery terminal and use an OBD ECU memory saver.

Keep in mind that some dealerships may void your warranty if you perform this task yourself. Check the terms of the contract. Ultimately, you’re better off using the warranty to get cheap or free repairs from the dealership. Let them make these adjustments. You can trust them to install new plugs if they break the old ones in the process.

Are There Specific Spark Plug Gap Tolerances For Different Vehicles?

The conventional gap setting for racing plugs is 0.4mm. But even though spark plugs are gapped at the factory, adjustments may become necessary because different engines have different requirements.

The Green Spark Plug Company has given the example of a V8 engine that uses pre-gapped spark plugs. Those pre-gapped plugs will require re-gapping in a 6-cylinder engine. Specific modifications may require unique gaps.

For instance, high-flow intake ports make ignition harder because of the charge swirl. A high RPM can also complicate ignition because the distributor doesn’t have the time to generate a robust spark.

The person who modified the engine should adjust the spark plug gap because they understand the engine’s requirements.

Recent Posts