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October 28, 2021

Professional Tool Reviews for Pros


DIY Spark Plug Thread Chaser Lifehack

Why Buy a Spark Plug Thread Chaser When You Can Make Your Own?

I pulled out my generator to make sure everything is ready for hurricane season when I discovered some damage to the spark plug threads. Even though they looked pretty good, the top few had some cross-threading damage and I couldn’t get the plug started to push through it. Since the damage wasn’t severe enough to need a full rethreading or Helicoil treatment, making my own spark plug thread chaser saved me a trip to the store and some money.



Tools Needed

Here’s what you’ll need before you get started:

  • Old spark plug of the same size with good threads
  • Dremel or other rotary tool (a file can work in a pinch)
  • Socket to fit your spark plug
  • Needle-nose pliers
  • Thick grease
  • Shop towels
  • Safety glasses
  • Gloves

How to Make a DIY Spark Plug Thread Chaser

Step 1: Break Out the Rotary Tool and Cut Some Grooves

Take your rotary tool and install a small cutting disk onto it. We like the Ryobi cordless precision rotary tool ($40). Another option is the Hart 20V rotary tool ($69).

Using it to cut a groove in your spark plug’s threads from the bottom as far up as you can without cutting into the hex head. Just make sure the spark plug has good threads.

Repeat every 90º around the threads. This creates a spark plug tap with 4 cutting edges around it. You may want to use a pair of gloves—that spark plug is going to get pretty toasty once you start cutting on it.

Step 2: Prep the Spark Plug Hole with Some Grease

Prepping the spark plug hole properly is critical to fixing it without introducing metal shavings to your engine. Start by adding some grease to the threads on both the spark plug hole and your homemade spark plug tap.

The goal of the grease is to get the shavings to stick so they don’t fall in and damage the engine while it’s running. For some extra protection, you can push a shop towel down far enough to let you work, but without letting it fall into the space below. Fishing it out won’t be too much fun if you do.

Step 3: Center the Spark Plug and Screw It in to Repair the Thread Damage

Here’s where it all comes together. Using your socket and ratchet, carefully center your DIY spark plug thread chaser so it can enter squarely and reopen the damaged threads. If you come in at an angle, you’ll cut new threads across the old ones and it’s game over.

Once you feel the spark plug tap engage the good threads, go ahead and give it a few turns to let it cut open and clean out the old ones. Just remember to avoid pushing your towel all the way in if you’re using one.

Step 4: Remove Your Spark Plug Tap

Now it’s time to remove your homemade spark plug tap. Once you do, wipe off any excess grease to carry your metal shavings away. If you used a shop towel, a needle-nose plier can help you get it out.

Step 5: Crank it Up

You’re ready. Pop a good spark plug in and crank up your engine to make sure it works.

That’s All, Folks!

On my generator spark plug repair, the engine cranked up right away. Keep in mind that this lifehack won’t fix every job that needs a spark plug repair. You’re still better off taking it to a mechanic for severe damage. If you want to give this a shot on your own first, try it and let us know if it worked for you!

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