Spark Plug Gap

There are few things that feel worse than trying to complete a job only to find out that you’re missing a tool. If you already have your car torn apart, the last thing you want to do is reassemble everything just to go and get the tool that you need.

In a fix and you don’t know what to do? Need to gap your spark plugs, but you don’t have the tools to do it?

In this guide, we’ll walk you through everything you need to know about spark plug gapping and how to correctly gap your spark plugs even without a gapping tool.

Why Do Spark Plugs Need to Be Gapped?

Don’t let the simple appearance of a spark plug fool you, they are fine-tuned components that are critical to your engine. While there are many internal factors that make a spark plug work, one that you can see is the spark plug gap.

Too much of a gap and the electrode can’t spark — which means your car’s fuel won’t ignite and you won’t get any combustion. However, too little of a gap, and there won’t be enough space for the air around the electrode to ignite, and you still won’t have any combustion.

Today, premium spark plugs come pre-gapped and as long as you buy the right spark plug from a quality brand, you don’t need to worry about gapping it.

But given the cost of replacement spark plugs, nobody’s going to blame you for choosing a cheaper option. Generally these aren’t pre-gapped, and even if they are, you might want to double-check the gap. That’s where this process comes in.

Keep in mind that if you don’t have the proper tools to gap a spark plug, it’s better to trust the pre-gapping instead of making rough adjustments and hoping for the best. Without the proper tools, it’s more likely that you’ll mess up the gapping instead of fixing it.

But if you have reason to suspect that the preset gapping is off –– then it might be worth trying to fix it yourself even if you don’t have a spark plug gapper.

Not only this but sometimes the tricks in this post can get you out of a bind. Getting home is more important than the perfect spark plug gap!

What Happens if You Ignore Gapping?

Whether you have spark plugs with the wrong gapping, or a lower-quality set where the gapping isn’t adjusted — you’re going to run into a bunch of problems.

Car running rich due to bad or poorly gapped spark plugs
If your car is running especially rich, you may have incorrectly gapped spark plugs.

Some of the most common ones are:

  • Engine misfiring
  • Rough idling
  • Engine knocking
  • Poor engine performance
  • Stalling
  • Difficulty starting your engine

If you’ve ever experienced the symptoms of bad spark plugs, it’s almost exactly the same.

If that isn’t bad enough, an incorrectly gapped spark plug could also reduce the long-term durability of your engine.

Best Ways to Gap Spark Plugs Without a Tool

When you have a workshop full of tools at your disposal, there are two tools you’ll use for gapping spark plugs:

  1. feeler gauges, and
  2. spark plug gapper.

Feeler gauges help you measure the gap — and it’s the most challenging tool to work around. Simply because the gap on your spark plug is very particular, and it can be hard to get the correct gap without an accurate measurement.

The spark plug gapper is what you use to make actual adjustments. Luckily, finding a replacement for this isn’t as tough.

Spark plug feeler gauges are cheap — you can usually find them for less than you’d spend on a 6-pack. But if you’re really in a pinch, there are a few different things you can use to try to bail yourself out.

Using Household Items

First, you need to determine the correct gapping for your vehicle.

This gapping usually falls somewhere between 0.028” and 0.06”. There are two common household objects you can use to gap your spark plug — but you’re going to need to get a little creative.

Pennies (coins)

Those two objects are a penny and a dime, and their measurements are as follows:

  • Penny: 0.06”
  • Dime: 0.053”

If you’re looking for a spark plug gap with either of those two measurements, you don’t need a feeler gauge. But if you’re looking for a different gap, you should probably invest in a feeler gauge or a spark plug gapper.

Trying to guestimate the gap can lead to engine damage and be more of a headache than it’s worth.

Powering Through

If you’re feeling a little stubborn or just downright strapped for time, you can start looking around your workshop to find different tools to use. The problem is you’re going to have to look up each object individually and measure the thickness.

That’s because not every flathead screwdriver has the same thickness — and that’s the case with most objects in your garage. You’ll need to find the exact model you have, and then track down the thickness dimensions and hope it matches up with what you’re looking for.

In many cases, you’re probably better off sticking with the pre-adjusted spark plugs before trying to make adjustments based on estimations.

Making the Adjustments

The good news is that the second tool is easy to workaround. That’s the tool that you use to make the actual adjustments. Yes — that’s an actual tool, and no, you don’t need it if you have a feeler gauge.

Using a small flat-tip screwdriver or a knife, you can gently tap the electrode to achieve the desired gap. Just be sure to avoid the actual tip of the electrode, as you can easily break it by prying on it.

Using a Spark Plug Gap Tool

If you cave and buy a spark plug gapper, the next step is figuring out how to use it. The good news is that it’s not just cheap to buy, but also extremely easy to use too.

Man gaps spark plug with a tool

Using the gapper is simple. All you need to do is slide the spark plug electrode opening into the gap opener and gently move it over to the smallest side of the gapper. Once it hits the 0.02” area, press the electrode down until it’s flush on each end of the gapper.

Next, you’ll need to slide the spark plug around the gapper until you hit the desired thickness. Rotate the spark plug back out and you’re good to go — move onto the next spark plug and repeat.

The best part about using an actual spark plug gapper is that you don’t have to guess if the measurement is correct. We can’t say the same for household objects like pennies and dimes because they aren’t always the same thickness or uniform throughout.

It can lead to small discrepancies that can have big results on your engine performance.

Who knows, you might find that a cheap gapper is worth having around just in case you need to make any future adjustments or repairs.

Our Verdict

When it comes to routine engine maintenance, it’s always best to have the right tools. But if you’re in a pinch and don’t have time to get the right tools, that doesn’t mean you have to throw in the towel.

With a bit of creativity and persistence, you can get the job done, even if you’re missing a tool or two. Hopefully, this guide helped you figure out the basics of spark plug gapping and how to gap spark plugs even without a gapper.

What tools do you use to gap your spark plugs when you’re in a fix? Let us know in the comments below!

Leave a Reply

Your email address will not be published. Required fields are marked *