Stripped Spark Plug threads

My mother has a 2000 Lincoln Town Car. Last year she had a mechanic change spark plugs. A few weeks ago one blew out of the head, of course it's the one in the very back. My brother drilled it & put some kind of sleeve on it and that too blew out.

They have thrown in the towel and looks like it's up to me to sort this out.

Do I have any options other than replacing the head?

Common issue... see it mostly with the 4.6/5.4/6.8L SOHC engines in the trucks and vans.

There are some repair sleeves, that when used along with the proper tools, work OK without major engine work. We do a lot of those.

But if you've tried installing something and tooefed the head, then you're done.

I would look into finding a good used engine. That will be the cheapest, easiest way out. Any of the car (except Mustang) 4.6L should work. So any Crown Vic or Grand Marquis.

Shame, as those are otherwise a pretty good engine. You do not want to take the head off. There is a huge amount of special cam and crank lock tools you'd need to buy, there are two timing chains, and you'll basically have to take the engine out anyway in a car.

It is 16 hours labor to R&R a head. 11 of that is R&R of the engine. One cylinder head is about $1400. Trust me, look for a good used engine. You can probably find one for less than $700 and have it swapped in a weekend.

Thanks oilhammer!!! I've been looking at ford and lincoln forums trying to find this out.

Good Ford stuff:

www.flatratetech.com

I've used the timesert kit before with much success.

Make sure the other spark plugs are torqued correctly as well. IIRC Ford calls for 12-14 ft-lbs. According to what i have found that is too little and may contribute to the problem. I torqued mine to 28 ft-lbs.

I put never-sieze on the threads, install to finger-tight, then add about 1/4 turn with the wrench. Never had a problem with one loosening or blowing out. Worked fine for the glow plugs I've done on the TDI too.

Rob Mayercik said:

I put never-sieze on the threads, install to finger-tight, then add about 1/4 turn with the wrench. Never had a problem with one loosening or blowing out. Worked fine for the glow plugs I've done on the TDI too.

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The FoMoCo Modular/Triton family of engines have a specific issue with plugs blowing out (2-valve) or sticking in and coming out in pieces (3-valve). It is unlike any other engine I have run across.

On the 2-valve engines it is pretty clear that they thought the head was cast iron, and not aluminum, yet it still has the typical 3 or 4 threads' worth to fasten the spark plugs like the old iron-head Windsor engines. So they blow out. We still see this commonly on the trucks and vans, as the E-van used the 2-valve engines right up until the Transit replaced it (they never got the 3-valve engines).

Were all 2v heads the 2-3 thread design?

oilhammer said:

The FoMoCo Modular/Triton family of engines have a specific issue with plugs blowing out (2-valve) or sticking in and coming out in pieces (3-valve). It is unlike any other engine I have run across.

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Any idea on what causes this?
I realize we have a design flaw..but this car went 100k miles in 17 years then a local mechanic changed plugs. 7 months or so later there was an overheat. The electric fan died and it spit coolant out while stopped. Then 4 months later it blows this plug out.

I'm not trying to go after the mechanic that would be a lost cause. Just thinking either he over torqued it, or maybe the overheat did it.

More than likely mechanic wasn’t familiar with that engine and it’s issues. From everything I’ve read he either torqued them to spec which doesn’t work or perhaps he cross threaded it.

If they are torqued back to spec and with only 2-3 threads the plug isn’t “biting” into anything. Just seated right where other plug was. Then pressure, vibration, and in your case an overheat and plug worked itself a little loose and that’s about all it takes.

1999-2002 engines have low spark plug thread count. 2003 and up have about double thread count but thread count but 3 piece plugs and break off in head. There are 2-3 companies that put out remedied plugs to replace Ford 3 piece plugs.

TdiRN said:

Were all 2v heads the 2-3 thread design?

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I know we've had 2010s in here that had plugs blown out. The trucks always seem much worse, but that may be because that is what we see the most of with these engines. Plus, they I'm sure get worked much harder... a loaded E250 with a 5.4L pretty much gets floorboarded by drivers who are not the owners. They also run them out of oil quite often.

If the engine overheated (which is common due to the old intake design, if it still had one, depending on year and model), then that certainly could have made the weak spot even weaker.

This is such a common problem that I would not look for blame outside of FoMoCo themselves, and since this engine design's roots certainly started way back in the late '80s, as its debut was 1991 (Town Car), 1992 in the Crown Vic and Grand Marquis, 1994/5 in the Mustang, Thunderbird, Cougar, 1997 in the E-vans and F-trucks, the individuals responsible for this design oversight have likely long since retired and have a very nice pension or whatever.

Like I said, I'd just look for a used engine. May not be easy to find given the car 4.6L is slightly different than the truck version, and the fact that the cab companies love to cobble retired POS police vehicles together for a half million miles, they may be either in short supply OR worth a lot more than they should be.