How to Gap Your Spark Plugs

The gap between the center and side electrodes of a spark plug must be an exact distance; otherwise, your plugs don’t fire efficiently. Adjusting the distance between the two electrodes is called gapping your spark plugs. You need a feeler gauge to gap your spark plugs properly.

Gap new as well as old spark plugs, even if the package says that the new plugs are “pre-gapped.” To avoid problems, work on only one plug at a time, in cylinder sequence order.

The following steps explain how to gap your spark plugs:

1Clean your spark plug.

If you’re regapping a used plug, make sure that it’s clean (gently scrub it with a wire brush). If you’re using a new plug, it should be clean and new-looking, with the tip of the side electrode centered over the center electrode.

You shouldn’t see any cracks or bubbles in the porcelain insulator, and the threads should be unbroken.


How to Gap Your Spark Plugs

2Select the proper number on your feeler gauge, and run the gauge between the electrodes.

To find the right gauge, look for a spec sheet for your automobile in the owner’s manual, or you can get the information from a local auto parts store. If the gauge doesn’t go through, or if it goes through too easily without touching the electrodes, you need to adjust the distance between the electrodes.


How to Gap Your Spark Plugs

3Adjust the gap as necessary.

If the wire didn’t go through, the gap is too narrow. Hook the part of the feeler gauge that’s used for bending electrodes under the side electrode and tug very gently to widen the gap. A feeler gauge is shown here.

If the gauge goes through too easily without touching the electrodes, the gap is wide. Press the side electrode very gently against a clean, mar-proof surface until it’s slightly bent down toward the center electrode.

4Run the gauge through the gap again.

You want the gauge to go through fairly easily, just catching the electrodes as it passes.

If you keep adjusting the gap too narrow or too wide, don’t feel bad. Most people go through the “too large–too small–too large” bit a couple of times for each plug, especially the perfectionists.

Leave a Comment

How to Find a Hidden Water Leak Under a Sink: A Simple, Safe Check

How to Find a Hidden Water Leak Under a Sink: A Simple, Safe Check

Use dry paper towels and four focused checks to find a hidden sink leak, tell supply leaks from drain leaks, and know when to call a plumber.

Why Does a Bathroom Mirror Keep Streaking After Cleaning?

Why Does a Bathroom Mirror Keep Streaking After Cleaning?

Bathroom mirror streaks often come from residue, dirty cloths, excess cleaner, or dried water. Find the likely cause and a gentle way to fix it.

How to Stop Condensation Forming Inside Windows Overnight

How to Stop Condensation Forming Inside Windows Overnight

Reduce overnight window condensation by controlling indoor moisture, improving airflow, monitoring humidity, and knowing when the window itself needs attention.

How to Reduce Kitchen Odors at the Source

How to Reduce Kitchen Odors at the Source

Reduce cooking and kitchen odors without fragrance by improving ventilation, cleaning grease and food residue, managing waste, and finding persistent odor sources.

Why Is My Ceiling Fan Wobbling? Causes and When to Turn It Off

Why Is My Ceiling Fan Wobbling? Causes and When to Turn It Off

Learn why ceiling fans wobble, which warning signs mean turn it off, and what you can safely check before calling an electrician.

Why Are My Indoor Plant’s Leaf Edges Turning Brown?

Why Are My Indoor Plant’s Leaf Edges Turning Brown?

Learn why indoor plant leaves turn brown at the edges, how to read clues about watering, humidity, salts, and light, and when to seek expert help.

How to Protect Stored Clothes From Humidity Without Mothballs

How to Protect Stored Clothes From Humidity Without Mothballs

Keep stored clothes dry without mothballs: measure closet humidity, reduce moisture at the source, dry garments fully, choose suitable storage, and inspect for mold.

Why Towels Smell Musty After Washing—and What to Check

Why Towels Smell Musty After Washing—and What to Check

Musty towels often point to lingering moisture, washer residue, or slow drying. Learn how a hypothetical laundry example helps narrow the cause and what to change first.

How to Water Balcony Plants While You’re Away for Several Days

How to Water Balcony Plants While You’re Away for Several Days

Keep balcony plants hydrated during a short trip with a plan based on pot size, plant needs, sun, and wind. Compare wicks, self-watering pots, and plant sitters.

How to Move a Heavy Houseplant Without Scratching or Denting the Floor

How to Move a Heavy Houseplant Without Scratching or Denting the Floor

Move a heavy houseplant safely without scratching hardwood, denting flooring, spilling soil, or straining your back. Use a protected path, a dolly, and a controlled team lift.