Help needed: damaged spark plug thread

I mustn't have torqued down the #3 spark plug (middle cylinder, passenger side) when I had last changed the plugs on my 4Runner. The plug worked itself loose and eventually popped out. My son who is the primary driver of the car noticed the issue with the CEL and that is when I learned about the plug once I removed the coil. In installing the replacement plug (new Toyota OEM plug), the plug went in a couple of turns and it then became hard to turn. I did not push it. The issue that I have is that the old spark plug, in working itself loose, appears to have damaged some of the thread in the spark plug hole. I used a mini camera to inspect the thread. I see some damage on the top but toward the bottom (engine cylinder side) the threads are OK. . I tried a thread chaser (ARES M14 x 1.25) which I believe is the correct size. The thread chaser goes all the way in fine by finger. I have even used the thread chaser several times with grease, .., etc but I still can not make the spark plug itself to go in. The plug goes in a couple of turns and then it becomes hard. Worst case scenario I may need to re-tap the plug hole and use a helicoil but I don't want to go there yet. Any thoughts on what the issue is and what I could do next? Am I even using the correct thread chaser? Thanks in advance.

 

https://www.ebay.com/itm/1558596496...cId=9312975&merchantid=111899346&gad_source=5

There's a good one there. Unless it specifies it's for spark plugs, it's not the right one.

BTW, a machine oil is what you want to use, not grease, when chasing/cutting threads.

If this device doesn't do the job, yeah, it'll be time to drill, tap, and helicoil. It's not really all that hard a procedure. I had to do it on an 87 4Runner I had. I just chased the other 3 holes, but it was pretty easy process. WITH a spark plug specific thread chaser. I got it at an Auto Zone, but in Yuma, Az, not here in Oregon.

Does this help?

 

Thank you Phantom Tweak for responding. I spent more time yesterday and still could not get the spark plug going in beyond 3 turns. After three turns it just spins in place which leads me to believe that the thread is damaged there but interestingly enough the thread chaser easily works itself through!. My next step to move onto a helicoil. There are several options on manufacturers/price range. There is one kit from Advance Auto (https://shop.advanceautoparts.com/p...m14x1.25-5334-14/9010505-P?selectedStore=3118) on one range. At the high end, I have also come across this one from Time-Sert (https://time-serts.com/store/m14x125-spark-plug-extended-kit-washer-seat-pn-4412e-111/) which at $264 is quite pricey. Personally I am willing to go with the higher price product if it does a better job and is more assured but I have never done a helicoil fix before. I guess I need to do more searching to learn more before I start the repair work.

 

If it were me, I'd use the Time-sert kit. It looks like it has all the tools you'll need to do the job, along with the instructions, which are vital for a first-timer.

https://www.rockauto.com/en/tools/ignition,tool,spark+plug+hole+thread+chaser,13059

Rock Auto has a virtually identical kit on this page to the Time-Sert. The one from Lisle Pro, for about $85.00. Much better price for the same tool kit. You might want to check that one out.

Good luck. Follow the directions carefully, and read over every step thoroughly before taking any action. Check all the cautions and so forth.

Have fun!
Pat☺

 

Hi Pat,
Not having fun but getting there. Out of curiosity do you know what length of a helicoil did you end up using? The kit that I have has three inserts, with the longest one being almost 11/16". One end of the helicoil is gnarled so roughly 9/16 of it gets threaded and the rest gets "flared" over the re-threaded hole on top of the cylinder head. Based on what I can tell, the edge of the helicoil will be right where the thread ends on the tip of the spark plug. To me this implies that the 11/16 size helicoil is the correct one but I wanted to see what you thought before I proceeded.

 

Following up, I have attached the picture of the insert that I have. This is not a helicoil but it performs the same function. Also based on what I have learned, the whole insert gets threaded in, including the gnarled area. The flaring is performed at the end.

 

I would use the one that just reaches the end of the threads on the spark plug. You don't want the zert threads to reach any further than that. Alternatively, the one that just reaches as far as the metal of the head. They should be about the same, but I might well be wrong.

Remember to use OEM spark plugs. That way you know they are the right length, and gap.

If you think I remember what I used on an 87 4Runner back in 1997 or thereabouts, that I sold a couple years ago, think again. Heck, I can't remember what I had for lunch yesterday!

If you're careful, it should work out right. Mine did, I remember that
Pat☺

 

Just adding this note to close this thread. The insert is in and is alright now. It remains to be seen how permanent a fix this will turn out to be.