It's a one piece insert, not a coiled piece of wire like a helicoil. It also has positive placement - meaning it tightens down against the head, rather than just being threaded into it like a helicoil - so in theory it can't come loose and screw it self in or out of the head (although, has helicoil ever had a problem with this?)
I'm sure a Helicoil will work fine if it's installed correctly, but this might be better.
A Helicoil for a spark plug, wouldn't that be more prone to leaking?
I have installed the inserts a few times, the really good ones that come with a threading tool that screws into the original plug hole, cuts and threads the hole for the insert and a punch that expands the head of the insert after it's installed.
And the really cheap ones from princess auto.
Both work fine but the expensive ones threading tool uses a large socket 17 or 19mm which won't fit where the spark plug goes, luckily the owner of the kit let me weld a 14mm nut to the end of the tool and the princess auto ones don't have a punch area and the insert can come out with the spark plug.
It's not that they were cross threaded. It's that the plug is seized in the head and after removing it, it will be full of aluminum curls that used to be threads. It was put in finger tight with anti-seize. But over the years and after being changed a few times the threads are worn.
This is exactly why helicoil was invented - the worn threads of aluminum aircraft engines that had plugs changed at specific maintenance intervals and eventually resulted in worn threads.
What I've been concerned about inserts is their expansion rate; helicoil will compensate being a wire insert, a ferrule much less. I'm worrying that with expansion cycling happening between the insert and the head and not insert and the spark plug, eventually some plug will thread out with the insert.
1988 626 GT Wagon, 2.0 DOHC Turbo | 1988 626 GT DOHC Hatch | 1992 Toyota Carina e GLi | 1991 626 GLX Hatch AWD 2.2l
What's the name of the better kit you used? Where did you buy it?
Helicoil was developed years ago specifically as a sparkplug thread liner for large aluminum aircraft engines.
I didn't buy the kit it belonged to the owner of the shop next to mine, Looked it up and I think it's the Helicoil save a thread non coil insert repair kit like this but his had all the sizes :
(Picture is example, not the kit for our heads)
STW they claim:
"The HeliCoil Sav-A-Thread Insert is serrated at the top. When this portion of the insert is
expanded, it embeds itself into the spark plug port and will never come out!"
The princess auto kit I tried had aluminum sleeves and no way of locking the sleeve in place, it comes out with the plug and because it's aluminum I can't grab the lip using vicegrips without destroying it, can try using JB weld or another sleeve.
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