Rounded and stuck sparkplug

Hey guys. First post I just (two days ago) purchased a 1991 B2600i 4x4. Went and did my usual new car maintenance oil change went fine, plugs in cylinder 4,3,2 go fine then I hit number 1. Round. The hex nut is round. So I hammer a socket on to it. And it's stuck... Like my breaker bar can't get it out. Anybody got any ideas? I need this truck for work.

Soak for several hours in penetrating oil. PB Blaster tends to be a favorite around here. If that doesn't work, put the other plugs back in and run the engine for five or six minutes to warm it up. Then try again.

If it was running OK before, maybe just leave that plug in there.

Some have used a longer, strong pipe over a breaker bar handle to increase torque (like me on VW 36mm nuts that are 220 ft. lbs., be aware of breakage danger).

Some might also suggest replacing the three plugs and then warming up the engine, then trying with that hammered-on socket and breaker bar.

I wonder if the threads had gotten screwed up, and someone used red Loctite on both sides of a solid threaded insert instead of just on the outer threads.

Anyway, a machine shop or even you could install a solid threaded insert to repair if such removal does damage original threads; I run such an insert on my 1835cc VW engine, and it's been fine for about 6 years now.

On my 1998 Frontier with 201K, I have a small piece of plastic way down in there in #1 that has prevented me from removing that spark plug, so I've just left that one be. Someone suggested heating up a spark plug socket and quickly pressing that on, to melt the plastic to enable the socket to grab. I have also considered gringing a recess on a cheap spark plug socket and trying that. Anyway, since it still runs nice, I leave it be; the other three plugs showed decent condition when I recently changed those for the first time (we bought that Frontier with 100K miles, maybe the plugs had been changed before we got it).

I'm still amazed that someone could actually round off the hex corners on these, even if a 12-sided deep socket was used instead of a 6-pointed sparkplug socket.

Thanks for the replys. Is there any kind of sleave in the head that the plug sits in? It looks like maybe it's sunk in to far. I posted a pic

If it runs good with it in now, no compression leakage through the plug from the porcelain being cracked after messing with it this time, I would replace the other plugs and hope that one is Titanium. "Ain't broke, don't fix it." Chances are, if you turn the plug now, the aluminum threads in the head will coming out with the plug.

When that plug starts missing, work on it, planning on possibly having to pull the head and carry to a machine shop for a boring (drilling out in a vise aligned to follow the original bored hole), since the threads may come out with the plug. They will either thread the new hole oversize hole (18 mm., I seem to recall) and screw in a heli-coil, or bore and plug it with a piece with original threads in it, like new.
Best case scenario, it comes out, threads still in the head and good, you coat the threads on the plug with never seize (a petroleum oil and graphite powder product), put it in and truck on. If this happens and there is any doubt about the threads, borrow or have a 14 mm. bottoming tap run down through the threads. Be sure NOT to cross thread it.
Good practice on aluminum head spark plugs is to always coat the threads on all the plugs with never seize, every time installed.

It's probably too late for this from the "rounding" you've described. But, after you've soaked the plug like SCL said, clean the exposed area off with some brake cleaner. Then put a liberal amount of valve bringing compound on inside of your socket and then try again. The grit in the compound will give you considerably more grip and torque before it slips. I have used in many times on bolts and especially phillips head screws that are already stripped, or are so tight that you can't turn them without slipping/stripping. It may be too late this time, but the technique works very well.

Just curious, were the other 3 overtightened as well?

Depending on your mechanical ability, you can buy a helicoil kit at amazon, parts house, etc.. No doubt quicker and cheaper than pulling the head. Be sure to blow (long nozzle on air gun) as much metal out of the cylinder after you helicoil it, before putting new plug in. Remember to have the piston close to the top of stroke, but not close enough to interfere with the helicoil operation.
Another choice, line up a machine shop that you can park at, that will install a helicoil for you if the threads do come out. Next will be getting the plug out at all, as flimsy as they get when the porcelain breaks down. Then it goes to a LARGE easy out, or the machine shop drilling the spark plug out, off of the engine, of course!
Just drive it, until it becomes a running problem. Once the spark plug is busted, no fire and maybe little compression, it becomes work on it and all that that may entail $.

Read in post 3 (2nd reply), I've used solid threaded inserts, to replace a helicoil that was professionally installed, like the inserts better.

Are you talking about oil burner plug extenders?