Spark Plug Threads
Thread Starter
Heel & Toe
Joined: Jul 2019
Posts: 23
Likes: 4
From: Gilbert, AZ
Spark Plug Threads
Has anyone here successfully repaired damaged/crossthreaded spark plug tube threads? Unfortunately during my header swap, one of the spark plugs would not hand screw back in. It did come out no problem. I attempted to thread chase the tube and I think that may have made things worse. The car is scheduled to go into the shop next week to get looked out, but I was wondering if anyone had a success story in using a helicoil, timsert, or any other repair of their head rather than replacing the head entirely.
Race Director
Joined: Jul 2005
Posts: 12,021
Likes: 3,556
From: Central MO
Has anyone here successfully repaired damaged/crossthreaded spark plug tube threads? Unfortunately during my header swap, one of the spark plugs would not hand screw back in. It did come out no problem. I attempted to thread chase the tube and I think that may have made things worse. The car is scheduled to go into the shop next week to get looked out, but I was wondering if anyone had a success story in using a helicoil, timsert, or any other repair of their head rather than replacing the head entirely.
Safety Car
Joined: Sep 2013
Posts: 4,355
Likes: 2,633
From: Draper Utah
Been there, done that... if a spark plug will not thread in you want to use a "Powerbuilt back tap" as it chases the threads from the inside to the outside and costs about $20. It has two benefits that should help you... the first is any debris cleaned up falls outside the head. The second is it begins on the good inside threads and cleans the rest up as it exits.
If you didn't mess the threads up to bad with a tap this item will fix you right up. Hope the helps.
If you didn't mess the threads up to bad with a tap this item will fix you right up. Hope the helps.
Race Director
Joined: Jul 2005
Posts: 12,021
Likes: 3,556
From: Central MO
Been there, done that... if a spark plug will not thread in you want to use a "Powerbuilt back tap" as it chases the threads from the inside to the outside and costs about $20. It has two benefits that should help you... the first is any debris cleaned up falls outside the head. The second is it begins on the good inside threads and cleans the rest up as it exits.
Safety Car
Joined: May 2011
Posts: 3,807
Likes: 508
From: Oshawa, Ontario
Has anyone here successfully repaired damaged/crossthreaded spark plug tube threads? Unfortunately during my header swap, one of the spark plugs would not hand screw back in. It did come out no problem. I attempted to thread chase the tube and I think that may have made things worse. The car is scheduled to go into the shop next week to get looked out, but I was wondering if anyone had a success story in using a helicoil, timsert, or any other repair of their head rather than replacing the head entirely.
Thread Starter
Heel & Toe
Joined: Jul 2019
Posts: 23
Likes: 4
From: Gilbert, AZ
Just to update everyone (or future people with similar problems):
The shop I took the car to was able to chase/tap the existing threads to get the spark plug seated correctly without any misfire. So far after 30 miles the car seems to drive perfect. Since I have a AA supercharger, they did tell me to not go full WOT as they fear the spark plug could back out (not sure this would happen but also not looking to find out...). I have been able to get into some boost and no issues at all. Saved pulling the head, for now...
I think if this were to happen again, knowing what I know now, I would start with a back tap and go from there. At some point, I will probably get the head machined and the spark plug tube done correctly when I do a port job on my heads.
The shop I took the car to was able to chase/tap the existing threads to get the spark plug seated correctly without any misfire. So far after 30 miles the car seems to drive perfect. Since I have a AA supercharger, they did tell me to not go full WOT as they fear the spark plug could back out (not sure this would happen but also not looking to find out...). I have been able to get into some boost and no issues at all. Saved pulling the head, for now...
I think if this were to happen again, knowing what I know now, I would start with a back tap and go from there. At some point, I will probably get the head machined and the spark plug tube done correctly when I do a port job on my heads.
Last edited by jpup; Oct 21, 2020 at 01:41 PM.
