How to Gap a Spark Plug

As we have said.

You should replace your spark plug at least once a year.

It is part of any standard tune-up and will make sure your engine operates correctly throughout the season.

So pick one up online or run down to your local lawn mower shop.

But before you toss your money across the counter, I want you to do something for me first. Give the box a little shake. Do you hear the spark plug sliding around inside there? Thought so!

The reason I point that out is because one of the most common questions we get when selling a spark plug is “Is it already gapped?”

And like most things in life the answer is of course…

“Well…sort of.”

You see during shipping the spark plug inside that box has jostled around for a while. And every time the electrode end bumped into the inside of the box it moved a hair, changing the gap.

The who moved the what?”

Sorry. Let me back up for a second.


Your spark plug is a pretty simple item. It has a few important features. But what we want to focus on today is the Center Electrode and the Ground Electrode.

plug electrodes simple

Engines need three things to function. Fuel, air and spark/ignition.

Spark/ignition comes from the spark plug. For the spark plug to ignite the fuel air mixture the electricity has to arc between the two electrodes of the spark plug.

For the electricity to be able to jump between the two electrodes the spark plug have to be at a very specific distance.

That distance is what we call the SPARK PLUG GAP.

When a new spark plug leaves the factory the gap has already been set. But as we have already established the whole “shipping shuffle” can bend the Center Electrode offsetting the gap.

To adjust the gap you are going to need a spark plug gap gauge.

We sell this little beauty which you can have shipped direct to your door.


Once you have your spark plug gap gauge it is time to figure out where to set the gap.

Most small engine spark plugs need a .030 gap but it can vary from engine to engine. If you are not sure consult your engine owners manual or give us a call or an email. We would be happy to look that up for you.

To use the spark gap gauge you insert the edge into the gap between the electrodes like shown below.

spark plug gap GUAGE

While keeping the guage in the gap slide the plug along the outside circumference of the gauge until both electrodes make contact with with the gauge.

This will tell you at what distance the electrodes are set.

spark plug gap GUAGE II

In the image above the Electrode begins in the .100 position and is slid clockwise until it stops at the .080 position. The gap on this spark plug is currently set at .080 mm.


Adjusting the gap involves bending the ground electrode in either direction until it is set at the correct distance.

The gap tool can be used to do this either by using the flat surface to push the electrode in (thus narrowing the gap).

moving the electrode in

or by using the center hole to pry the electrode outward (widening the gap).

moving the electrode out

Be careful not to bend the electrode too far or too quickly. They can break.

Setting the gap on your spark plug is as easy as that! So get online and order your new spark plug and your spark plug gap tool now!

They make great gifts for your DIY’er.

Do you have questions or comments about gapping a spark plug? Please feel free to contact us via email or phone.

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How to gap a spark plug
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How to gap a spark plug
Engines will not operate correctly if the gap is not set. It is easy. Learn how.
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Jack Hayes

Jack Hayes is the Head of Internet Marketing at LawnMowerPros and the editor of this blog. You can often find him creating featured articles, DIY guides, custom graphics and much more.