What is a Spark Plug?

What in the world is that? It’s a Spark Plug!

Ah, the majestic spark plug.

Simple, compact, elegant. It’s not where the magic happens, it’s where the Wizard that makes the magic happens was born!

Many folks look at the spark plug and think the same thing….I ain’t touchin’ it. I don’t know nothing about it…and I ain’t touchin’ it.

Yeah, me too.

So, let’s rob the spark plug of it’s power over you and talk just a minute about what it is and how it works.

A quick look on the inside

So there are eight basic parts to the spark plug; the terminal, spline, center electrode, insulator, hex nut, body, gap and ground electrode. All of them work to accomplish the same purpose:

  • To safely conduct electricity from the source to the inside of the engine
  • Regulate the amount of electricity conveyed to the engine
  • Create a spark – make the gas go boom

As an engine owner, you probably won’t end up dealing with most of these components. But there are three that we should pay close attention to: the Terminal, the Gap and the Ground electrode. Those are the parts that can become corroded, causing the spark plug to fail. (See: How to Read a Spark Plug for more information).

Let’s take it from the top
The terminal is the initial connection from the source. The most important thing to know is that over time corrosion can set in, interrupting the connection. When this happens, the electricity can’t get through. First: Disconnect the spark plug and remove it from the engine!! (Trust me, you don’t want to get shocked.) A rag or brush will remove any loose debris, and a little carburetor/injector cleaner or mineral spirits will work to remove any stubborn build up. When in doubt, replace the plug.

Explosions cause a mess
When the electricity travels through the center electrode to the Ground electrode, it arcs across the distance between the two. This distance is called the “gap”. The arc is a tiny little fire that ignites the gasoline inside of the engine resulting in that big-badda-boom. But explosions can leave a mess, and over time this carbon build-up can cause the spark plug to fail in a multitude of ways. This is a common problem for spark plugs, but it can be taken care of:

  • Disconnect the wire from the spark plug.
  • Next, clean up any debris around the spark plug before you remove it. We don’t want that stuff falling into the hole that the spark plug goes in.
  • Now, remove the plug by using a spark plug socket wrench.
  • Take a look at the gap. If it’s dirty, a wire brush and spray on cleaner will help to remove build up. More stubborn debris can be removed by using a knife.
  • If you see any damage to the plug (cracks, burns, pitting or melting), go ahead and replace it.

A little adjustment here and there
Here’s where it gets a little scientifical…so bear with me.

The ground electrode is made of metal, but it tends to be a bit soft. Because of this, it is very easy to move the ground electrode from its original position during cleaning.

“Does it matter?”

You bet it does! The distance between the ground electrode and the terminal determines the amount of spark produced by the spark plug. Bad gap=bad spark. So it’s important to check the gap before re-installing the plug.

  • The gap is normally checked with a spark plug gauge, which can be picked up at almost any automotive parts store. We also offer this gauge.
    Simply insert the gauge into the gap.
  • Move the gauge to the appropriate gap setting and ensure that both the terminal and the ground electrode connect to the surface of the gauge.
  • A typical gap for small engine plugs is 0.030″. If you’re not sure, consult the manufacturer.
  • If you continue to have problems, just go ahead and replace the plug.

So, there you have it. A little bit about the devilishly clever spark plug.

And we keep plugging away!


LawnMowerPros.com carries a bunch of different spark plugs for top brands such as Briggs and Stratton, Honda, John Deere, Kawasaki, Kohler, MTD, Murray, Sears, Snapper, Toro and many more. SHOP SPARK PLUGS.

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Bill Brown

Bill is the head of content creation for the LawnMowerPros Blog and DIY section. He’s been in the Outdoor Power Equipment Industry for years and he’s still learning new things everyday. You can often find him creating featured articles, DIY guides, videos, graphics and much more.