I was coming close to 100k on my 2004 JCW and thought it would be good to change the spark plugs, since I recently purchased the car and don't know when they were changed last.

I took them all out, and the fourth one came out a little rough. I pulled it out and it's threads were covered with a brown deposit. Worried me a bit..

After replacing the first three, from left to right (with new iridium plugs / NGK BKR7EIX), I got to the fourth plug and tried to thread it in. It wouldn't go.. I decided to compare the new iridium with the old regular JCW plug. The original JCW plug (NGK BKR7EQUP, just like the previous 3 plugs) had a bigger diameter threading! Even though it had the same plug name stamped on it.. Since I couldn't find anything online about this, I cleaned off the threads and replaced the fourth cylinder with the old JCW plug. Now it's 3 iridium plugs and the one old one.

Has anyone experienced this?? Did the previous owner force a larger diameter plug into the whole and caused a rethread? Totally confused about what's going on here and if it's something to be concerned about..

Thanks everyone. Happy Motoring!

Best,
Hg

 

could be you have a helicoil repair and the insert came out with the plug

 

Yep, that's gotta be a helicoil kit, no way it could have been a forced rethread (threads would be mangled). Someone must have stripped it out previously and repaired with a helicoil, no other options really. The coil backed out with the spark plug. That sucks, but you should be able to get a new helicoil kit to match whatever it has been re-threaded to.

 

Got it okay.. Well I put the original plug back in and it went in fine.. torqued normally. Not sure what to do now though.. I'm trying to contact the previous owner to get the specs on the helicoil / timesert that was put in, so it can potentially be rethreaded.

This still doesn't explain why the plug was a larger plug though.. I have been unable to even source the type of plug it is, as it is spec'd the same as the rest on the label, but simply has a larger diameter thread.

Thanks for the insight guys.

 

It probably has the helicoil stuck onto its threads, making it look like one larger piece.
If you take it out, I'll bet you can screw the helicoil off of the plug and then it will look
like the other three.

 

Ahhh yes you were right! I didn't get pictures but it was very similar to what you showed in your photo. Except the helicoil does not overhang the plug at all, so it appeared to be the same piece. I also found that the coil has fused to the plug.. I'm hoping I can get a replacement that is the same diameter, to just put around the new iridium coil?

 

+1 on the helicoil stuck. Nice thinking cristo.

 

I realize this thread is a month old, but I wanted to chime in to say that I had the exact same problem. A previous owner had repaired stripped spark plug threads with a helicoil - and the plug was ejected from the head (with the helicoil still on it) while I was on my way to the airport!

After my trip, I successfully repaired the threads with a time sert kit. If you haven't fixed this problem yet, I encourage you to try installing a time sert.

The writeup of my experience is here:

https://www.northamericanmotoring.co...il-repair.html

My original thread asking about how best to repair stripped spark plug threads (which is full of the same sorts of recommendations you've already gotten) is here:

https://www.northamericanmotoring.co...questions.html

You can often find the Time-Sert 4412E kit (for M14x1.25 spark plug threads) lightly used on ebay. (That's where I ultimately sold mine.) Barring that, Amazon usually has a decent price.

And if you need any help, feel free to ask.