Repairing a Blown-Out Spark Plug Using the Save-a-Thread HeliCoil Repair Kit (With Video)

Updated on October 2, 2018
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Hardlymoving writes about do-it-yourself automobile maintenance on various makes and models.

Example of a Save-A-Thread Heli Coil Repair Kit
Example of a Save-A-Thread Heli Coil Repair Kit

This article, with segmented videos, will show you step-by-step how to re-thread a spark plug hole and insert a thread tap so that you can insert a new spark plug that will stay in place in the cylinder head.

A thread tap makes the spark plug hole larger while creating new threads. Then a new insert, also called HeliCoils or TimeSerts, is threaded and torqued into the enlarged hole. High temperture RVT is applied to the insert threads to prevent it from coming out. The new spark plug is then threaded into the hole of the insert.

After I diagnosed a blown out spark plug in my customer's Crown Victoria, he went out and bought a "Save-A-Thread" kit containing a thread tap with 3 different lengths of HeliCoils. I picked the HeliCoil that matched the length of the spark plug threads and screwed it into the tapped hole. Once I locked the HeliCoil in place, the threads inside the coil, matching the threads of the spark plug, allowed the plug to be torqued back into the cylinder head without coming loose.

The blow-out of the plug damaged the ignition coil pack, so I replaced that as well.

You only need basic tools when using the repair kit:

  • 3/8" long extension
  • 1/2" socket wrench
  • 1/2" to 3/8" adapter

You will also need high-heat-resistant RTV sealant to coat the threads of the HeliCoil.

Video: Repair Overview

Step-by-Step: Using the Spark Plug Save-A-Thread Heli Coil Repair Kit on a Ford Crown Victoria

The videos below, with text instructions, will show you step-by-step how to re-thread a damaged spark plug hole on a Ford Crown Victoria and insert a HeliCoil.

1. Tap the Spark Plug Hole with the Save-A-Thread Tap Tool

  • Remove the coil pack.
  • Remove the spark plug.
  • Attach the save-a-thread tap tool to a long 3/8" extension attached to a 1/2" to 3/8" adapter.
  • Insert the attached tap tool into the spark plug hole. Turn the tool by hand until you feel reistance.
  • Attach the 1/2" socket wrench to begin cutting the new threads.
  • Keep turning until the tap tool bottoms out, at (I'm guessing) around 60 pounds of torque.
  • Screw out the tap tool and exam the threads of the tap tool for metal shavings. There should be shavings on the cutting areas around the length of the spark plug threads.

Video: Tapping the Spark Plug Hole

2. Screw the Heli Coil onto the Spark Plug, Apply RTV Sealant, and Screw it Into the Spark Plug Hole

  • Select the HeliCoil that matches the thread length of the spark plug.
  • Screw on the HeliCoil onto the spark plug.
  • Apply RTV to the threads of the HeliCoil.
  • Drop the spark plug with the HeliCoil attached into the spark plug hole.
  • Using a 16 mm or spark plug socket, torque down the spark plug. High torque will spread out and seat the top of the HeliCoil into the cylinder head.
  • Remove the spark plug. The HeliCoil should be flush with the base of the spark plug hole and should not come out with the spark plug.

Video: Screwing on the Heli Coil Onto the New Spark Plug, Applying RTV, and Screwing in the Plug

3. Inspect the Seating of the HeliCoil and Re-install the Spark Plug

  • Using a flash light, inspect the base of the spark plug hole. The HeliCoil should be flush with the base.
  • Remove any RTV reside on the spark plug porcelain.
  • Re-install the spark plug. Apply approximately 20 lbs of torque.
  • Install the new coil pack, assuming that the old coil pack was damaged from the blowout.

Video: Inspecting the Seating of the Heli Coil and Re-installing the Spark Plug

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    © 2018 hardlymoving

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