Strange spark plug thread size

Hey TW,

new to the forums and I was going to do an intro post but I was changing my spark plugs for the first time and found something really strange.

I pulled the three on the passenger side and 2/3 new K16TR11s went in totally fine, but one wasn’t threading.

at first I thought it was the threads in the hole were stripped, but I tried putting the old plug back in and it threaded in fine.

then I took a look at the old one side by side with the new one and it seems the thread size is larger even though it’s also a

$18 K16TR11 Spark Plugs, Pack of 4

K16TR11.

what’s strange is the other new plugs went in just fine, but this one hole seems to have larger threads, possibly from someone forcing the larger threads into it?

new and old plug picture attached any help is much appreciated!

 

Do you have calipers or a micrometer to measure the diameter of the threads? Does the thread pitch match? Hold the new one against the old one to see if the threads match, as in mate with each other.

 

The threads seem to mate, but the micrometer showed the old one was a good bit larger than the new one.

I’m at autozone right now and here are the micrometer pictures of each plug.

New one:

Old one:


they think someone might have put a sleeve on the old one?

suggested I just clean it with starter fluid and throw the old one back in for now

 

That’s a helicoil on the old plug. I don’t know if they can be reused.

 

Yup, second pic of post 3, can now clearly see the helicoil came out with the spark plug.

If you don't know what helicoil is. Means the spark plug hole in the head was stripped & repaired with helicoil. The helicoil is supoosed to stay in the head.

 

Ouch that sucks.
Edit: get another helicoil to fix it.

 

ah okay I understand now, what do you guys suggest I do?

I’m fairly new to working on cars and didn’t think just swapping out the spark plugs was going to give me this much grief!

 

Buy a pack of them. Helicoil is just a brand. Few company’s make those.

 

gotcha, and do I need to cut all new threads, or just put the new helicoil on the plug when I install it?

Sorry if this is a dumb question, like I said I’m fairly new and learning.

 

Don’t have to cut (should not either)anything you do need to buy the right size. And yea I’d Check out time sert I think I’ve seen some that once threaded in they bite on the head and generally don’t come out. You don’t want the sleeve to small or to big to stick out past the threads

 

Dude thank you so much!

gonna look into time sert and will update this thread when I get it installed.

appreciate you guys helping me out on my first post, and I’m stoked to be part of the community!

 

What needs to be done is the helicoil that came out needs to be properly replaced in the head. I say "properly" meaning that so it won't come out again the next time you take the spark plug out.

BTW Helicoil is a brand name & is what most everyone just calls it, you know like Band-Aid, Kleenex, etc. There are different brands & styles. Anyways, I've used helicoil many times but I've never needed to repair a spark plug hole with it before.

Helicoil requires drilling & tapping new threads with the included STI tap. After installing the coil insert with the tool, you are supposed to break the tang off the coil that the insert tool uses to drive the coil in. Now the metal savings from drilling/tapping & the tang that needs to be broken off can very easily fall into the cylinders which of course you don't want.

Again I've never repaired spark plug holes so the proceedure must be different to prevent that. Good thing is you won't have to do the drilling & tapping, just needs a new insert installed but again I'm not sure about the tang. They must not use the tang, too risky falling in. The thread inserts are stainless too but not sure of they are a magnetic grade of stainless.

If you don't have much experience working on cars, I would carefully put the old plug back in & take it to a mechanic. If you want to try yourself, search online & watch some YT videos.

 

Yeah I was looking at some YouTube videos and the drilling / tapping part definitely intimidated me haha

do you think installing it via the plug is a bad idea? Even using these time sert ones that apparently bite into the head like @Smokestacks was mentioning?

I think if that’s not an option I’ll probably follow your advice and carefully thread in the old one and have a shop handle it.

 

Yea just put the sleeve onto the spark plug. And treat it like the rest of spark plugs no need to be nervous. Even if they come out like that don’t really matter just sucks bc you gotta replace the sleeve.

 

The old plug honestly looks pretty good, electrode is still strong.
I'd put it back in if it threads easily and snugs down.
Best thing is actually a new head and she good as new.
Something to save for during the next 30k miles.

 

Installing another helicoil style insert would be the easiest since they all require the use of a STI tap. STI taps are specifically for thread repair coil inserts. Which means you don't have to do the drilling & tapping cause it's already been done. I forget but Timerserts are different & larger than helicoils, if yes then you'd have to tap & drill.

"Installing via plug"? Is that how they do it? That makes sense cause I don't see how they can be installed using the break-off-tang type. If that's the case, should be easy. Cause the kits are expensive, just the coils not so much.

With helicoil you're not supposed to use any sort of threadlocker. But for spark plug hole repair I'm not sure if that's different. Look that up. Because of repeated temperature cycles & removal of the spark plugs might be different. Or just put the helicoil on the plug everytime you need to change it.