Broken spark plug

It is almost impossible to cross-thread a spark plug. You'd have to really grunt on the ratchet to get it to screw all the way in like that. The mechanic would recognize that right away, stop, and try again. We always start spark plugs by hand, so we'd know if we had one cross-threaded.

What IS real common is for the threads to become stuck to the head, especially with aluminum heads and the newer spark plugs that can last over 100,000 miles. Most mechanics use anti-seize compound on the threads to prevent this problem.

At this point most likely the remaining part of the plug will need to be drilled out. The best way to do that is to remove the head and do the work on a workbench, but if you have sufficient access, you might as well try doing it on the engine first. As you drill a larger and larger hole and get close to the threads, you may be able to crush the remaining part by tapping on one spot with a hammer and flat chisel. Once part of the threads breaks free and starts to collapse, that will pull the rest of the spark plug's threads away from the head's threads.

If you drill far enough to damage the head's threads, the repair may actually become easier. Once the old spark plug is out, if the new one won't become tight due to the missing threads, use a Heli-Coil kit to make new threads. Anyone at any auto parts store will have the kit with the correct size drill bit and spring insert. If they can't explain how to use it, I will.

Once you're done drilling, (regardless if it's the head or the old spark plug), use a long piece of metal rod or wooden dowel with a glob of grease on the end and poke it around in the cylinder to gather up the chips. Ground out that spark plug wire or unplug that ignition coil so there's no spark, then run the engine for a few seconds with that spark plug not installed. That will help blow out any remaining chips. The aluminum and steel chips will work their way out anyway through the exhaust system, but I'd be nervous if there were ceramic chips in there from the spark plug insulator. Those are real hard and could scratch the cylinder wall.

To back up for a minute, if you aren't to the point of drilling yet and there is still a way to grab the old plug to try to unscrew it, you might try a penetrating oil to loosen it up. A real good product is Chrysler's "Rust Penetrant". It comes in a spray can and will do in 20 minutes what WD-40 will do in a weekend. It comes out black, and it sizzles a little. The only issue is you must wash it off when you're done. When I started doing alignments at a dealership, I used this on the tie rod ends to insure the next person would have an easy time getting them apart to adjust them. What I found when cars came back in six months or a year for a maintenance alignment is I needed a torch to get those parts loosened up. I learned that the oil opens the way for moisture to follow it in later and make the parts even more rusty. I know other dealers' parts departments have a similar product with their own name on it. I only know the Chrysler product.

As a last resort, I've welded nuts to broken parts, but I've never done that yet to a spark plug. I can paste a copy of a reply if it comes to that. The high temperature and the shock from dribbling a little water will help to crack the threads apart, then the nut will give you something to grab with a socket.

If it is able to be moved even a little, all the penetrating oil might do is dissolve some corrosion that is impeding your progress. If you've drilled far enough, the shell with the threads might be expanding under the pressure of your Easy-Out. That is a problem with the type that is tapered and has spiral teeth that grab as you turn it counter-clockwise. That makes the shell bind more as you try to turn it. There is a different kind that is a straight metal rod with grooves cut in it. You pound those straight in, then slide the mating nut over it. That nut matches the grooves and gives you something to turn with the socket without expanding the shell.

To figure out the largest drill bit size that is safe to use, look on the package for the Heli-Coil kit. That comes with the right drill for this application. You want to drill perhaps no larger that 1/16" to 1/8" smaller than that. Reason is you want to save the threads in the head. Once you get the shell out, run a spark plug tap in a few times to clean out any metal chips and corrosion.

The Heli-Coil drill bit will be larger because you DO want to remove the threads. Well, actually, you want to remove the steel from the old spark plug and corrosion from the threads in the head. The second step of the Heli-Coil process is to run a tap into the hole to form new threads. This results in the threaded hole being too big. Next, you wind in a stainless steel spring. This part of the job is real easy but there are things to watch out for so don't start this before I share that wondrous wisdom with you.

The spring has threads on the outside that match the threads you just cut in the head. It also has threads on the inside that match the threads on the spark plug. This is a permanent repair that is much stronger and more reliable than threads in aluminum. It's real common to need to do this on Ford truck engines. Those spit spark plugs and threads right out of the heads.

If you can move the shell with a needle nose pliers, you might also try pounding in a very fat flat-blade screwdriver to use as a handle. Here again, the goal is to avoid expanding the shell, but even if it does expand, it will only be tight in two places instead of all the way around.

I'll be back in a minute with another reply.

This is a copy of a reply I've posted before The first sentence doesn't apply to your situation, but the rest of it might make a good bedtime story and leave you with some new ideas. Substitute a bolt with a good head on it in place of the nut in this sad story.

I had a broken bolt exactly like yours on my '88 Grand Caravan a few years ago. It created the perfect "teachable moment" for my students and especially the kid who felt bad for breaking it. You'll need a wire feed welder and an acetylene torch. Propane torch won't work. The flame is too large and not hot enough. Grab a nut with a center hole slightly larger than the bolt diameter. Center the nut over the broken bolt. Use a small torch tip with a nice blue flame with a sharp point. The tip of the flame is the hottest part of the flame. Touch that tip to the center of the bolt to warm it up. The goal is to get the bolt red hot but it never will get that hot because the heat is being sucked away by the intake manifold. Nevertheless, heat the bolt for at least a couple of minutes. Stay away from the nut as much as possible. You want it to stay cool. If you're careful and quick, you can heat the bolt first, then set the nut in place with a pliers just when you're ready to weld. When the bolt is as hot as it's going to get, hand the torch off to a helper and immediately grab the welder. Feed the wire onto the end of the bolt and start to build it up. Stay away from the nut as long as possible. Don't stop welding because you don't want the bolt to have a chance to cool down. As the weld builds, it will fill the hole in the nut and eventually you will also be welding TO the nut. The nut will turn orange. That's ok, but stop welding before the sides of the nut start to melt. You need those sides to be in good shape so a socket will fit on the nut.

Welding works, not by "sticking" to the metal, but by melting the surfaces of the two pieces of metal with a filler metal in between. That's called "penetration". If you don't preheat the bolt, the heat from the welder will be sucked away before the metal of the bolt melts. You'll end up building up the weld until it melts to the nut but it won't have penetrated the bolt. That would be like putting glue on the piece of wood you're using to build a bird house, then assembling the pieces after the glue dries. The preheating gets the bolt up to its melting temperature sooner. It has to reach that temperature from welding before the weld builds up to the nut.

Once the nut is welded to the bolt, let it cool by itself for, ... Oh, ... About ten seconds, then dribble a little water on the nut. Don't pour so much that it floods the surrounding area. You want to shrink the bolt but leave the intake manifold hot. The shock from the water will help break the bond between the bolt and intake manifold. Use a six point socket, ratchet, and extension on the nut to turn the bolt out. If the weld didn't stick to the bolt and you twist the nut off, just grab another nut and try again. I've already had to resort to as many as six attempts before this worked. Sometimes this works better with two people, one to run the torch and one to be standing ready with the welder. Use a high setting on the welder to insure good penetration into the bolt before the weld builds up to the nut.

If that doesn't work, you can also drill out the bolt, even alongside a broken Easy-Out, then install a Heli-Coil insert. If you've never done one or seen one, any auto parts store can show you what to do. The Easy-Out really should be removed to insure there won't be a leak later. You should be able to remove it once a hole is drilled beside it. You'll need to drill or grind the mating hole in the thermostat housing off-center to line up with the new bolt hole. I did this a couple of months ago for one of the bolts for the distributor cap on my '88 Caravan. On mine, the hole went all the way through the mounting flange but yours is a "blind" hole. That means it doesn't go all the way through. You can reach your finger through the thermostat hole to gauge how thick the metal is you're drilling into. Don't panic if you drill all the way through. That just means you'll need some gasket sealer to be sure it doesn't leak, but it will make getting the metal chips out easier. Use compressed air, a magnet, or a little grease on the end of a stick or Q-Tip to remove the metal chips. If there's too many chips left in there after drilling, the tap will but t up against them and won't cut threads all the way to the bottom of the hole. That COULD cause the new bolt to bind at the bottom of the hole and make it appear tight when it isn't really drawn all the way down yet. (To be safe, use a new bolt that is shorter than the hole). Once the hole is drilled with the drill bit that comes with the Heli-Coil kit, you use the supplied tap to make new threads.

Once the tap has gone in a few turns, back it off a quarter turn to break off any chips, then go another quarter to half turn. Keep doing this until you feel the resistance suddenly increase a lot. That means you're but ting up against the chips that fell to the bottom of the hole. Unscrew the tap and clean the chips out again, then run the tap down once more. You'll feel the tap get tight just like a bolt gets tight. Don't force it. I can't remember if your intake manifold is made from aluminum or cast iron. If it's aluminum, it will tap very easily, but it will be easy to peel the new threads off too if you force the tap once it becomes tight. Blow the chips out again so the bolt won't but t up against them.

So, blow the metal chips out after drilling so the tap will go in all the way, and blow them out again after tapping so the bolt can go in all the way. The insert is a wound-up stainless steel spring. The outer part forms threads that match the threads you just cut. The inner part forms threads that match the new bolt. There is a plastic tool in the kit that threads onto the insert, then you use that to wind the insert into the hole. The insert will shrink as you wind it in since it is just a spring. You'll be able to do that with just two fingers. There are two important things to watch for. First, you must wind it all the way in so no part of it sticks up above the surface of the intake manifold. If it sticks up, the thermostat housing will sit on top of it and be held up. There's a chance the gasket won't be thick enough to seal the gap. If you can't get it to screw in far enough, either the hole must be drilled deeper or you can try again with a second insert. Use an air cutoff tool to cut off one or two coils at the top of the insert. What's left will be plenty sufficient to do the job. To remove the first insert, grab the end of the coil with a needle nose pliers and twist it counter-clockwise. If it refuses to unscrew, which sometimes happens, twist and tug on it at the same time to uncoil it.

You can also use a cutoff tool to carefully grind down any part of the insert that is exposed above the surface of the intake manifold.

If you drilled all the way through to the cooling system, wash the threaded hole with brake parts cleaner or carburetor cleaner, then wipe a little gasket sealer inside the hole and on the outside of the insert. Use more sealer on the bolt threads. Stick everything together before the sealant sets up, typically 10 †15 minutes. If you didn't drill all the way through, no sealer is necessary, but you might consider coating the bolt with a tiny dab of anti-seize compound to prevent more trouble in the future. Coat the other bolt too after cleaning the threads with a wire brush. I don't like grease on the bolts because the heat causes it to lose its lubricating properties and it can migrate away from the bolt over time. Anti-seize compound stays put. Be sure to blow out any rust or corrosion from the other bolt hole.

Be sure both gasket surfaces are clean of old gasket material or sealant. When you have a stamped sheet metal thermostat housing, place a sheet of sandpaper on a piece of glass or other smooth surface, then slide the housing across it. There is a slightly raised ring on the housing sealing surface. If you see that entire ring is shiny from sanding, it will seal against the gasket. I also like to put a thin layer of gasket sealer on both sides of the housing gasket. That helps it seal if there are small gouges or sanding scratches from cleaning the metal surfaces. That gasket will peel off easier next time. The Chrysler dealer's parts department has two sealants that I'm real familiar with. The gray stuff gets harder and will seal through a film of oil on the metal surfaces. It is a little harder to clean off the next time. The black stuff remains a little more rubbery but it is easier to remove. It will not bond and seal if there is any oil film present. That makes it not desirable for use on transmission pans.

As a last resort, look for a nearby community college with an automotive program. We had a few dozen people in our community who would sit on a car with a problem for months until it fit what we were teaching, then we used it for demonstrations or to provide the kids real-world experience. They typically will not take your car in if it doesn't fit what they are currently studying because that would put them in competition with the employers who hire their graduates. You would be responsible for getting the truck there, and you could expect to have to leave it for a few days. Often there is a small charge but it will be very insignificant.