Hardlymoving writes about do-it-yourself automobile maintenance on various makes and models.
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.
You can use a thread tap to make the spark plug hole larger while creating new threads. Then you take a new insert—also called a HeliCoils or TimeSert—thread it, and torque it into the enlarged hole. You apply high-temperature RVT to the insert's threads to prevent it from coming out. Then you thread the new spark plug 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
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 HeliCoil 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 flashlight, 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
This article is accurate and true to the best of the author’s knowledge. Content is for informational or entertainment purposes only and does not substitute for personal counsel or professional advice in business, financial, legal, or technical matters.
Questions & Answers
Question: What about the chips from cutting the new threads? Where do they go inside the cylinder?
Answer: When you use lubricant on the cutter, the chips will stick to the cutter and the threads.
Question: What if I don't have RTV to apply? Can I retread and install a spark plug without RTV?
Answer: Then I highly recommend you get the high temp, high strength RTV before installing the helicoil.
Question: What is RTV and what can I use in it's place?
Answer: RTV is liquefied synthetic rubber that when exposed to air, it solidifies. It is mostly used as a substitute for gaskets.
Question: What is the punch used for?
Answer: There's no punch. You're cutting new threads for the spark plug insert.
Question: So you don't need to use the expanding tool?
Answer: Not that I'm aware of.
Question: Does the HeliCoil Repair Kit contain RTV?
Answer: Nope. You'll have to buy it. Recommend the Permetex gray RTV.
© 2018 hardlymoving
hardlymoving (author) from Memphis, TN on April 28, 2020:
Okay ... good luck!
Bob on April 28, 2020:
Thank You for the great video, it gave me the answers I was looking for. Wish me luck.
Mike on May 21, 2019:
Thanks for the straight forward steps.
I think I’ve done it correctly. I’ll find out tomorrow after I’ve let the RTV set.
Sabrina Gray on April 30, 2019:
Omg where have you been all my life. Lol. This is exactly what ive been needing to know and out of all sites ive visited and folks I've spoke with, YAL ARE ABSOLUTELY 100% THE BEST EVER!!!!!!!!!!!!!!!!