Hi, so I bought a used 2005 4.6 v8 a few months ago. I was doing some routine maintenance and replacing the spark plugs. I noticed the rear spark plug on passenger side had an insert. The insert width is like the typical helicoil diameter but the outside threads don't line up, the are slightly more spaced out. The inside threads are regular M14 1.25 but the outside threads are a big bigger. Anyways, I tried to buy several brand inserts like the calvan (too big), the timesert and the helicoil both have the correct diameter but the thread on them is smaller. They all fit on the spark plug but don't thread onto the head. Is there any recommendations on this how to get the correct insert? Or is my only option to redrill a bigger insert like the Calvan?

The old insert appears stuck the old spark plug and some of the threads are damaged. It is also a different brand as the other spark plugs so it looks like someone replaced all the plugs, had same issue as me and just left the plug in there, only changing the other plugs. So that's why I wanted to replace it, probably the plug has been there for a long time.

I would maybe spray it to see if I can get it loosened but the old insert is not useable but I do have it to compare/ find another replacement thread. Additionally, since the threads on the insert are damaged maybe the threads on the head are also slightly damaged. I was thinking if I can find the correct insert, I could also use a chaser to see if I can fix any damage to threads. Alternatively, I would have to use a bigger kit like the calvan to redrill.

 

I would attempt to contact the previous owner to see if I (you) can gather some historical info on the insert that is presently installed. If you are able to identify the type of insert used you may be able to obtain removal instructions. Maybe?

 

I bought it at a county car seized auction lol so good luck to me finding the old owner. But the old insert is on the spark plug when removed, all i need to do is find a replacement insert, is there a web site where I can buy an assortment of insert sizes?

or how do I measure the exterior threads? They are like 1.4-1.5mm spacing. When I look up inserts they go by the inside measurements but they don't seem to specify the exterior diameter and thread pitch

 

Post some pictures.
There are many people in this Forum who have years of experience dealing with insert repairs.

 

awesome idea let me put some pics and a small video, maybe the thread is same but maybe it just gives illusion of larger threads 🤔

 

Here is a short video. Diameter is same as standard time sert or the save a thread (helicoil). I don't think the video uploaded but the diameter is same as the smaller inserts

 

Measure the major diameter of the insert threads (the od) then if you don't have a pitch gauge you could very carefully measure from the crest of one thread to the crest of the next one..should be 1.0mm or 1.25mm or 1.5mm something like that need to decide which is the closest number then the thread size is ODxpitchi.e. 16x1.5