Tapered Seat Spark Plug Horror

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awesomeissquid

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Today started like any other nice weekend with plans to leisurely work on the truck. On the agenda was replacing the spark plugs since their age was unknown. Starting with the passenger side it was going smoothly except for some slightly stuck plugs that took some coaxing. The horror show started at the rear most plug. The plug extracted easy enough, but looking down the tube I saw mangled bits of metal, cue some choice four letter words.

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At first I figured this must be part of the spark plug threads, but looking at the plug I found that someone had mistakenly installed a tapered seat spark plug instead of a gasket seat one, cue more choice words. Side note, incase anyone is curious our trucks take gasket seat types and the two are not interchangeable. My first thought was that some of the taper seat had just broken off in the hole since I found a bit of jagged metal on the seat. Unfortunately, upon pulling the pieces out with a magnet, it appeared part of the threads in the cylinder head (I think?) had broken lose.

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After calming down some I decided to continue cleaning out the hole to see how it looked. I got it as good as I could (slightly better than the over picture) and decided to use one of the other old "correct" spark plugs to see if it would even thread in. This seemed to work so I went ahead and installed the new plug. At the better judgement of my partner, I held off on starting the engine until I can get some advice. So now for the part where I ask for help, what do I do?

I figure there are two ways this could go. Option A, is the new spark plug is able to seat against whatever is left down there and will work fine. Option B is that the part (whatever it is) needs to be replaced. Looking at part diagrams this looks like it might require a full new passenger side cylinder head. Does anyone have any advice they would care to share? Since it was somewhat difficult to see due to other hard piping in the way I have been thinking about getting one of those scope cameras to stick it down there and take a look at it.
 
Somebody else wrote a post yesterday about his spark plug blew out. The advice he was given from the forum members was to use a helicoil. He wasn't sure if the threads were damaged, but the dealer indicated they might be. (They offered him an expensive fix, probably a new head.)

A helicoil is used when the threads are stripped. I think you can get it in a kit, with the correct drill bit, a thread tap, and the helicoil. You then drill out the spark plug hole, and use a tap to rethread the hole. Then you install the helicoil. Then you install the spark plug.

You have to be pretty careful to catch as much of the shavings as possible, and vacuum out the rest. Since it's going to be aluminum shavings, it won't do as much damage as steel would, but you should still try to get as much out as possible.

I wonder if the PO installed that tapered thread spark plug because he knew he had stripped threads!
 
Are you sure that it has not already been helicoiled?

That metal on the magnet and top of the plug looks like it might be the remains of one. See how well a new correct plug threads in there and report back please.
 
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Are you sure that it has not already been helicoiled?

That metal on the magnet and top of the plug looks like it might be the remains of one. See how well a new correct plug threads in there and report back please.
I agree. The photos look like an old helicoil/timesert that came out.
 
I had seen that other post but didn’t put two and two together about that being an option. I will need to do more reading on what that is exactly to understand what I would be looking for or what I might be seeing.

The new spark plug went in without issue after I cleaned everything up. Would this not happen if it had been helicopter? I torqued it per the FSM and stopped there. The previous owner was very hands off so it was definitely done at a shop but must not have been the dealer.

Looking closer at the shavings that came out I believe they are parts of the first few threads the spark plug screws into. My guess of this is the taper part of the old plug crushed them down and they broke off when it was torqued down. I know they had to be under the spark plug because I vacuumed out the tube before I removed it. Here is a poor sketch of what I think happened.

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Regarding the use of helicoils or similar:
Let's say a previous owner cross threaded a plug in the head or otherwise really fubar'ed the threads. You can drill out the cavity and tap it to a larger size, then thread an insert into the larger threads reducing it to the original size. This is not an ideal solution for a combustion chamber IMO, but needs must and some do.

To the best of my knowledge, these are usually made of a ferrous material and hence would be magnetic (whereas the aluminum head would not be). Also, once done I suspect this should make the 'base hole' too large to accept an original size plug.

If the new plug fits properly in the clean hole, then I have no idea what was in the cavity but count your lucky stars.
 
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If you cleaned out the spark plug hole and able to thread the new one in correctly, get the most precise torque wrench and torque it to specs, factory says 13ft lbs. I see no reason why it would damage anything if you can torque it to specs, go ahead and start the engine.

This is debatable but i set my plugs to 20ft lbs and i do not use any anti seize. I did my old LC to 20ft lbs and 100K miles later they were still nice and snug when i did a tune up again. Now on my LX that i got a year ago, dealer serviced, i suspect they used the factory 13ft lbs torque and when i got to it, all of them could be spun out by hand. Either the plugs back offed over time or the tech's torque wrench is as accurate as the weather forecast.
 
Thanks for explaining about helicoils! I agree that I would prefer to not have to do that and am lucky the threads inserted smoothly.

At this point what happens if I were to start the engine and the gasket was not fully seated? Is there a way for me to tell if the gasket is not fully seated?

My guess is that if there is a gap in the gasket seat it would allow some combustion products to leak around and into the tube. I assume this would be similar to if the spark plug had backed out slightly?
 
You'll hear what sounds like a manifold tick, if you rev it a little it'll sound like a sewing machine
 
@MUDZLLA that is a fantastic point. This is making me think that I need to pull the plug and get a scope to look down the hole to actually see what is there.

edit: I guess I will need to look if there is a helicoil of some sort there and if there is if it is a tapered one or a flat top one.
 
I was recently in similar situation with the oil pan drain hole being stripped. I was debating between helicoil and timesert but decided to go with timesert kit. It was my first time ever having to re-thread anything and I couldn't recommend the time-sert kit enough. I was very well built and easy to use. There's something about the metal coil of the helicoil kit that I couldn't get my mind at ease to use it being afraid that the coil would someone brake over time and get into the engine.
 
Time serts are a much better choice for something like a drain plug which are going to be off and on a bunch. The downside is you have to remove more material to install vs a helicoil which generally only step the hole up a small amount. Thats probably not a problem in a lot of cases. I think I would probably helicoil a spark plug hole if I could, unless the head was off. In this case though since the threads appear fine and the plug threads in, I’d do nothing.
 
Time serts are a much better choice for something like a drain plug which are going to be off and on a bunch. The downside is you have to remove more material to install vs a helicoil which generally only step the hole up a small amount. Thats probably not a problem in a lot of cases. I think I would probably helicoil a spark plug hole if I could, unless the head was off. In this case though since the threads appear fine and the plug threads in, I’d do nothing.
From the pictures, it seems like the tappered part of the spark plug lost to the engine head while being torqued. I would do nothing as well because there's enough threads to keep the plug tightened and sealed to the engine block. In fact, I think it's the metal gasket that is on almost every spark plugs that was broken.
 
I used a helicoil on my rear sway bar bracket, has held up nicely and there is a lot of flex given it's the sway bar. If properly installed, a helicoil is dang strong, folks with f150's that spit plugs have used them for years.


 
Went to the store today and picked up a borescope camera. Not the clearest image and not entirely able to to determine what is going on.

Looking at the new spark plug that I pulled out it looks like crush washer did compress and I can see a marking where the edge of the assumed broken thread bit into it.

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@sacman I think your thought is correct. I dug through the trash to pull out the old plug to take some more pictures and it definitely looks like part of the taper got pulled out.

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I think this could account for some of the metal debris I pulled out but I think some of it was also part of the threads in the engine. Maybe a helicoil was installed but I am just not sure. I am going to keep trying to clean it up some more to see if I can find any more answers.

I will probably go out and get another spark plug since I have already torqued this new one down and I want whatever gets installed to have the best chance of working.
 
can you shove your magnet down there to block the hole, then use a long pick tool to remove that debris that is left?
 
The heads are aluminum so you certainly didn't pull out some of the threads with a magnet. My best guess (hard to tell via pics) is that it's part of the tapered spark plug. If a new spark plug threads in fine I say run it and check periodically to make its not backed off.

I think it's unlikely that someone with the skill and know how to install a helicoil would install an improper spark plug.
 

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