# Stripped sparkplug?



## Twenty five ought six (Jan 7, 2010)

I usually change the plugs on my old truck.  A few months ago, I had some work done, and had the plugs changed by the garage.

Today, I had to take them out.  This is a 300 Cu. in, in-line six, cast iron head, so other than some access problems taking the plugs in and out is no big deal.

Well it was like they were welded in.  5  & 6 were really hard to get out.  I'm talking both hands, hanging on the wrench hard. Some other issues, which I may come back to.  Anyway when I went to put the plugs back in, they wouldn't go.  I've done this several times, and usually the plugs go right back in.

So I fiddle with them about half and hour, and then look at both closely.  The threads (lead thread in particular) were stripped.  I was able to chase one, and get it back in but I've given up on the other one.

So question -- would over tightening by the so-called mechanic cause the threads to strip.

I'm pretty sure I didn't strip them taking them out.


Here's some pictures, and you can clearly see where the lead thread is crushed.







Here you can see where the thread is flat and shiny instead of sharp and black like the other threads.






Look at the bottom of this picture and you can see the spacing between the threads and the flattening of the lead thread.


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## GoldDot40 (Jan 7, 2010)

If the 'mechanic' was the last one to install them....he most certainly is the one who stripped it.....most likely caused my over tightening it. What's beyond me, is exactly how tight did he think it needed to be.

Stripping plugs is fairly common.....on an aluminum head. But even then, it's usually the threads in the actual cylinder head, not the plug. I don't think I've ever seen a spark plug with stripped threads unless it was cross-threaded. Yours really doesn't show evidence of cross-threading.....that had to be from over-tightening.

Have you tried a NEW plug in the head yet? Those old iron Ford heads are tough. You may get lucky. If new plugs won't thread in, I wouldn't chase them with anything that 'cuts' the metal. There are thread chasers out there that have continuous threads. They're made to just 'straighten' the damaged threads without cutting and creating metal shavings.....unlike broken thread taps like you'd use to drill and cut new threads. The cylinder head may ultimately need to be removed to repair the threads if they're bad enough.


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## Twenty five ought six (Jan 7, 2010)

Bassquatch said:


> If the 'mechanic' was the last one to install them....he most certainly is the one who stripped it.....most likely caused my over tightening it. What's beyond me, is exactly how tight did he think it needed to be.
> 
> Stripping plugs is fairly common.....on an aluminum head. But even then, it's usually the threads in the actual cylinder head, not the plug. I don't think I've ever seen a spark plug with stripped threads unless it was cross-threaded. Yours really doesn't show evidence of cross-threading.....that had to be from over-tightening.
> 
> Have you tried a NEW plug in the head yet? Those old iron Ford heads are tough. You may get lucky. If new plugs won't thread in, I wouldn't chase them with anything that 'cuts' the metal. There are thread chasers out there that have continuous threads. They're made to just 'straighten' the damaged threads without cutting and creating metal shavings.....unlike broken thread taps like you'd use to drill and cut new threads. The cylinder head may ultimately need to be removed to repair the threads if they're bad enough.





Thanks.  Haven't tried a new plug yet -- have a 5 cyl. truck right now, waiting for mama to come home.

I don't think the threads in the head are affected.  Like I said, I was able to dress the other plug and put it in the hole this plug came out of.  I just have never seen the threads on a plug buggered up like that.

I don't know what the mechanic was thinking.  I always put plugs in until they are "just tight".  Besides this is a relatively low compression engine.  I have no idea why he would put the plugs in that tight.  I've never had to use two hands to get the plugs out.  Even after I broke the plugs free, I had to use two hands, and I was really afraid of breaking a plug.


I think I cracked the head, so it all may come to naught anyway.


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## Steve762us (Jan 7, 2010)

You probably already got fresh plugs, but I wouldn't try to put the same ones back in.  A new plug won't thread into that last cylinder?

How's your relationship with that shop? Been going there for years?  Sometimes "going back in" can be worthwhile, sometimes it ends up worse--I've had it go both ways!


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## 5HwnBoys (Jan 7, 2010)

Yep go back to the shop and hopefully they'll make it right by you. Happened to me with my expedition. The spark plug came out one week after they changed the plugs. I brought it back only to have them tell me it was a common thing with the Expeditions .

They fixed it then Charged me for them installing a heliacoil
Sorta like what the Union Does (JOB SECURITY)


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## redneckcamo (Jan 7, 2010)

Sounds like maybe someone didnt have a clue how tite plugs should/shouldnt be....

I would definitely try new plugs an go from there !!


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## SGADawg (Jan 7, 2010)

It looks like the plugs have the right length threads, but if plugs with too-long threads are used, carbon can build up on the threads extending into the cylinder and cause problems similar to yours on removal.

Check to be sure those were the right plugs.


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## irocz2u (Jan 7, 2010)

thay  do make  a  thrade chaser  for  plugs just  magnatize  it


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## 7MAGMIKE (Jan 7, 2010)

Some people think I am a little over the top about this but spark plugs have a torque and should be torqued to that spec.  If the mechanic has a heavy hand he can over torque them the fix can be expensive especially on early model Ford 5.4 aluminum heads which had 3 threads in the plug hole. From what I understand Ford redesigned those heads .  On my Chevy 350 cast iron heads 22lbs ft. not much more than seating the plug and bumping the ratchet handle a bit.


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## Redbow (Jan 10, 2010)

I always crank the engine and let it warm up a little before removing a spark plug. Never stripped one out yet ! But I have seen it happen many times ! And 7mag is right you can over torque them pretty easily !


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## cravens62 (Jan 10, 2010)

*Stripped spark plug/Bad thread pitch*

The pictures (especially the last one) tells the tale! Because access is limited some mechanics will cram the plug in the spark plug socket add the extention and ratchet and proceed to force the plug to start threading itself in. Very poor maintenance practice! Back up a minute...Always inspect the threads on the new plugs. Sometimes they are bad from the manufacturer but more often than that, bad lead threads like your plug definitely shows, are from dropping them on the floor, distorting the thread pitch, thus causing them to cross-thread on installation. On aluminum heads this can be disastrous! In the future I would recommend chasing the threads out in the head to remove carbon (coking) and ALWAYS start the new plugs by hand or by hand with a spark plug socket and extension and follow up with a torque wrench! I also like to use a thin coat of high temp anti-seize. Your plugs probably were over torqued but that wouldn't cause that lead thread only to be distorted. I would show that spark plug to those rascals at the garage and tell them that spark plugs are not meant to be SELF-TAPPING!!!


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## 00_Green (Jan 24, 2010)

Cross threading or over torquing should have smoked the threads from one end to the other.  I think there was thread damage in the head that then damaged the plug causing it to be hard to extract.

If too long of a plug was previously used the end thread would have been exposed to the chamber and carbon would have built up on the last thread. During removal it would have damaged the bottom most threads until it was cleaned off. The new plug would then thread in until almost bottomed then hit the damaged threads and it would damage it's last threads as it was torqued.
It happens and these will always thread in easier than they will come out.

Same situation if too short of a grip plug was previously used. The bottom threads in the head would have carbon in them.  The correct plug would then be threaded into the carbon galling the threads as it was torqued. Again, installation would be far easier than extraction.


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## Twenty five ought six (Jan 24, 2010)

All of the plugs were very hard to get out.

I purchased the thread chasing tool referred to above (thanks for the reference) and chased the threads.  New plugs went in smooth as grease, and I was able to basically finger tighten.  I don't know if mechanic used an air wrench or not, but . . . .

Anyway, now that I have new plugs in seems that I've cracked the head or blown the head gasket.

On to bigger and better than things ----


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## beretta (Jan 24, 2010)

SGADawg said:


> It looks like the plugs have the right length threads, but if plugs with too-long threads are used, carbon can build up on the threads extending into the cylinder and cause problems similar to yours on removal.
> 
> Check to be sure those were the right plugs.



I have to agree with SGADawg. I have seen this before. Carbon bulid up due to poor cylinder performance, too much fuel,oil burning and coolant. This is a sure sign of some problems in those two cylinders.


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## beretta (Jan 24, 2010)

Run a compression test first with all of the spark plugs out. What cylinders are not firing? Are next to each other?


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## Twenty five ought six (Jan 24, 2010)

beretta said:


> Run a compression test first with all of the spark plugs out. What cylinders are not firing? Are next to each other?




I'm going to run a compression check as soon as I can and it quits raining.  Oh, to have a garage.

I'm pretty sure I know what it is, just don't want to think about it.  This engine is built like a tank but if it overheats, it tends to crack the head between nos. 5 and 6.  I'm hoping it's just the gasket and not the head.  

Don't think it's the block because no real funny sounds, no water in the oil.

The plugs were the right ones.  Due to high/thick head, and shrouded valves, they are long.


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