Spark Plug Threads Messed Up

[yippee]

I had posted pictures of my spark plugs in the past after changing them out. #2 plug had some rust on the threads. I replaced all of the plugs at that time. I pulled the #2 spark plug again to check it to see how it was looking. The spark plug was pretty difficult to get out. I let it soak over night in PB Blaster. Turned until it start to bind up, then thread it back in slightly, and continued this process until I eventually got it out.

I fear that the threads may have been messed up due to the rust or something (I am always VERY careful when threading anything in to make sure they don't bind up or cross thread). Any resistance and I stop and start over. Anyways, the new spark plug threaded in fine, but removing it was a chore. Either way it is out, and I want to know what to do next.

The threads in the head seem to be clean at first since you can start the spark plug without any issue, but it starts to bind up towards the end. The last few threads on the newer spark plug are messed up (pictures to follow). I have been reading around and seem to get the idea that you can 'chase' the threads in the head with a certain tool, or that you can 'tap' the threads, depending where you look.

I guess my main question is what size hole and what thread pattern do I use for the spark plug holes in a 3.7L Liberty? Has anybody used this method to save the threads in the hole?

Pictures as promised, kind of hard to tell, I know:

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Thanks!

 

[Royy]

The thread pattern is M14x1.25

I haven't had to do this on my KJ, but I had to do it twice on my last vehicle, an '03 Ford Explorer. Certain Ford engines are notorious for spitting out spark plugs, and messing up the threads in the head in the process.

I used this kit: https://www.amazon.com/Helicoil-533...icoil+5334-14+Save-A-Thread+Thread+Repair+Kit

It basically taps a wider thread in the hole, and the insert (with the proper thread for the spark plug) then screws into the wider thread, and is then locked into place with the punch. Worked like a charm both times.

 

[tommudd]

NAPA has a thread chaser that will clean the threads, you more than likely don't need to replace them just clean
Just take plug in and they will be sure to get the right one

 

[Conundrum2006]

The thread pattern is M14x1.25



I haven't had to do this on my KJ, but I had to do it twice on my last vehicle, an '03 Ford Explorer. Certain Ford engines are notorious for spitting out spark plugs, and messing up the threads in the head in the process.



I used this kit: https://www.amazon.com/Helicoil-533...icoil+5334-14+Save-A-Thread+Thread+Repair+Kit



It basically taps a wider thread in the hole, and the insert (with the proper thread for the spark plug) then screws into the wider thread, and is then locked into place with the punch. Worked like a charm both times.

For some year fords there was a class action, got a card in the mail informing me our truck could qualify if we had receipts and god knows what else.
But we had replaced the motor by then with a rebuilt that supposedly fixed this problem. The old motor had two bad spark plug ports, one the nearly ejected the spark plug when I caught the sound they make and checked it.


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[GunnerSchenck]

Last year about this time I replaced my buddys plugs for him in his 03 mustang.. While removing them I told him "hey, whoever put these in cross threaded two of them (I knew he did it) and you're gunna want to chase these threads before we put the new ones in"
He opted to say something along the lines of "I only need it to last one more year, it'll be okay"
Well, within 3 months his engine said F U and spit his plug straight up through his hood lol. Blew the ignition coil apart into a couple dozen pieces and ruined his shaker intake

 

[Leeann]

NAPA has a thread chaser that will clean the threads, you more than likely don't need to replace them just clean
Just take plug in and they will be sure to get the right one

This. Mine is double-ended, actually.

The chase will work - you need to clean existing threads, not cut new ones.

 

[yippee]

Great, that's what I was hoping for. I'll get one of my old spark plugs out and run up to Napa to grab this tool. I was hoping I could just chase the existing threads since most of them seem to be good. We'll give that a shot and see how that works out.

I know they recommend using grease on the tool to trap the shavings from falling down into the cylinder, what type of grease is best to use? I have the grease that I used to repack my bearings on the front end of my truck, not sure if that would work or if I need to pick up another grease while I'm out.

As I'm working the tool through the threads, keep backing it out periodically to clean the tool/grease and add fresh grease (in order to minimize the shavings). Anything else to add to this?

What is the best way to clean the final threads once this procedure is done, before installing the spark plug again?

Thanks.

 

[Leeann]

Any grease will be fine.

 

[yippee]

https://www.napaonline.com/en/p/SER3379

Is this what I'm looking for?

What's the best way to get the grease off of the threads in the head once the job is complete?

 

[yippee]

Looking on Napa's website, I see a few different options. I was wanting to get some opinions on which one would be best before I go pick up the parts to tackle this job. Here are some options:

$12.14
https://www.napaonline.com/en/p/SER3379

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OR

$30.59
https://www.napaonline.com/en/p/SER2123

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Obviously the second one is more money, but it is also tapered at the end - I wasn't sure if this was better/more preferable, or if the cheaper one would handle the job. I'd rather pay more if it will do the job better, but at the same time I don't want to needlessly spend the extra money if it isn't going to gain me any benefits.

 

[HoosierJeeper]

My uninformed opinion is that once it's threaded in, the tapered tip won't matter, so I'd probably just get the first one.

 

[Dave]

We have a local NAPA and the people working there are pretty knowlegable, so if it were me, I would just go over there and ask what the difference is. I would suspect one is made in another country with cheep steel and the other in the USA with stronger steel. I don't know if this is the case here but I have personal experience with lower quality tools failing. All steel is not created equal.

I don't know for sure but just my thoughts on it.

Dave

 

[turblediesel]

The tapered tip is more likely to cross-thread and it might contact the piston if it's near top-dead-center.

I'd use the other especially if the initial threads on your plug hole provide a good start.

Taps are a different beast. Taps are usually available with three different tapers. A tap tapered like the one in your photo is a "starting tap" and a tap with a blunt tip like your other photo is a "bottoming" or "gun-tap"; used to thread to the bottom of a blind hole.

Other tap considerations... Three and four flute taps help center the tap in the hole. Some taps are designed to push chips ahead of the tap, others are designed to pull chips back along the shank of the taps. "Backing" a tap when cutting new threads serves to break any continuous chips forming at the teeth so chip pieces can make their way up the flute channels. You only need to back the tap in an arc about the width of the flute channels.

Might want to wave a little retrieval magnet inside the plug hole to grab any loose rust dust before you start chasing the threads.

Sounds like you're being carefull enough, good luck!

 

[yippee]

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Thanks gents, for the help. I went with this one ^ and it seems to have done the trick. I first made sure it would thread into the the first threads without issue cause I didn't want to make things worse. Fit the existing threads with no issue. I greased it up and slowly started working it in, backing it out, cleaning threads and reapplying grease until I had worked my way all the way through the threads.

Seems to have worked exactly as designed with no issues, it went a lot smoother than I expected. This was my first time using one of these, so I had a bit of anxiety about it not working right or making it worse. Went smoothly and seemed to do what was intended with minimal effort.

I gapped a new plug (didn't want to use one with wonky threads), put some anti seize on it, and carefully threaded it in per normal procedure. Felt like it went in much smoother than previously. I guess we'll keep driving it and see what happens. Hopefully next time we have to change plugs we won't have any further issues.

Thanks again for all the help and pointers. Hopefully this fixed it for good.