This is probably a stupid question, but how does throwing a spark plug cause damage and what kind of damage? I've had plenty of plugs malfunction and plug wires go bad over the years in older cars causing cylinders not to fire, but never had any damage result.

Also, are there any warning signs that your engine might soon throw a plug?

 

I'm confused as to what you mean by throwing. Throwing, as in blowing out of the head, or throwing as in causing a dead skip. Either case ain't good; the former will usually destroy the COP (if equipped) and the threads in the head. The latter will overwork the COP/coil pack and may eventually kill it.

 

I mean as in coming out of the head. How does this happen exactly? Does it unscrew from the head, or is there a thread failure? And what is COP?

 

I have the 5.4 Triton. When a spark plug comes flyin out, it takes the threads from the alluminum block with it. I know this from experience. Unless you find somone with the special tool (which is quite costly, so hardly anyone has it), you're not only going to pay someone to re-tap the cylinder, you're going to pay them to remove the heads too. It ain't cheap, fortunately, I found someone with the tool (saved me about $600).

 

One should always try to search a subject, this has been covered, recovered and beaten to a bloody pulp, and then shot and hacked to pieces with a machete

The answer if it happens is this apparently

It appears to be a total crap shoot as to whether it happens to any single owner, but since the issue is based on a common sense design flaw, it's one Ford should take care of (but obviously isn't).

I used to work a lot with engineered products that had to meet multiple rigid government and professional standards as they came from the factory, the variance in properties from the engineering specs was quite large, so the designs took into account the deviations from spec and compensated by building in a healthy tolerance.

In Fords case, an engineer was arrogant enough to believe his numbers said 4-5 threads will do and didn't compensate enough for the variances in materials properties and manufacturing processes, the rate of failure directly correlates to the percentage of product coming off the line out of spec since it doesn't appear to be related to any other external factor.

 

COP is the coil on plug. The compression of the engine usually pops the plug out and breaks the coil at the point where it's bolted to the intake manifold. Ford's official stance is that you're supposed to replace the cylinder head if there's any damage to the spark plug threads. My '97 F250 LD popped #3 out at around 120K-something, and I replaced the head. Companies make inserts that you can install to repair the damaged threads; had I known about that, I would have bought that kit instead of a new head and all the attaching parts for it.

 

Did you try a helicoil? I've never heard it mentioned. I've stripped out spark plug threads on a 5hp engine and a helicoil fixed it.

 

My #3 plug blew out at about 92K (after I had changed plugs at about 72K). It destroyed the COP and stripped the threads out of the head. Fortunately for me, it happened as I was arriving home. The truck was paid for, and I hadn't had to put any real maintenance money into it at that point. I didn't want to either. I went out and rigged up a couple of tools, and bought a helio-coil kit. The rigging was to take a reamer/tap (it is tapered to ream out the plug hole first, then tap new threads into it) and have it welded to a cheap extension. The last thing I wanted to happen was to have the reamer/tap get stuck in the hole, and not be able to retrieve it (I have the 5.4L). With the tools and helio-coil kit, I had about $17 invested. After I reamed and threaded the plug hole (couldn't even see what I was doing in my garage, didn't have a drop light), I put Loc-Tight on the outer threads of the helio-coil (two came with the set) and screwed the plug into the inner threads. Then I ran the plug into the head. I was told that you are supposed to blow out (with compressed air) the shavings from reaming/threading the head, but I don't have a compressor in my garage. Put the new COP on ($64) and fired it up. Heard a few tink, tink noises from the exhaust ( I assume it was the head shavings). The truck ran fine. I had invested about $81 in this fix. I was sacred as hell to change the plugs after that, but at 200K, I finally changed them. The truck now has 213K on it, and runs smooth as silk. Doesn't burn any oil, has plenty of power. I always try to do my own maintenance, but this was the first time I had done something like this. I am not a Mechanic by trade, I work in Information Systems.

Given what others have had to pay for this situation, guess I'm lucky, eh?

 

"The rigging was to take a reamer/tap (it is tapered to ream out the plug hole first, then tap new threads into it) and have it welded to a cheap extension."

That's what I wanted to do, but had no access to a welder.

"I was told that you are supposed to blow out (with compressed air) the shavings from reaming/threading the head, but I don't have a compressor in my garage. Put the new COP on ($64) and fired it up. Heard a few tink, tink noises from the exhaust ( I assume it was the head shavings). The truck ran fine."

You got really lucky those shavings didn't scar the cylinders.

"Given what others have had to pay for this situation, guess I'm lucky, eh?"

Yeah you are! Good job!

 

What about throwing, as in with your arm.

 

Only if it bounces off your truck and clips you in the face

 

If you put some grease on the tap/reamer it'll catch a lot of the shavings in the grease instead of dropping them inside the cylinder therefore preventing any concerns of shavings in the cylinder.