Hi all.

Quite a while ago, a spark plug blew out of my '96 Cobra. The dealer said Ford had a problem with this on pickups, but it wasn't a known problem on Cobras. Nevertheless, it happened.

The incident wrecked the threads in the block, but the dealer repaired it with a Helicoil and the car seems to have been fine since.

Today it was time to replace the spark-plug wires, and of course the plugs. I found that one of the rubber connector assemblies didn't want to slide over the spark plug and sit flush against the engine the way the others did. I tried another connector, but had the same problem. I also tried reinstalling the plug. I suspect that this is the hole that was repaired years ago (it's on the correct side).

I replaced the wires before, but don't remember this happening. I may have simply dismissed it, but now I'm concerned that the plug is actually not screwing into the block as far as the others, because of the repair. I've attached a picture showing the connector plunger in question.





Wouldn't it cause a performance problem to have a spark plug not extending into the cylinder properly? Any suggestions on what to check or do about this? The car does seem to run fine, but of course subtly reduced performance may not be noticeable.

Thanks.

Gavin

 

You're probably fine...they may not have run the insert completely flush to the head?? Remove those 2 plugs and look down the well to see how they compare!!

As far as performance....you won't see any difference kinda like indexing plugs...no real world advantage!!

Good Luck!!

 

OK, thanks for the reassurance!

I did look down there, but the well is too deep and the angle of view too limited to see whether the area around the hole is raised more than the others.

I considered taking a measurement from the hole perimeter to the top of the well, but figured I'd post a question about it here before bothering. And there's not much I can do about it anyway, I guess.

 

Can you examine the plug hole using an angled dentist's mirror and good flashlight? imp

 

That's an interesting suggestion. It just so happens that a friend of mine makes dental instruments, and I have a mirror lying around. The well is pretty narrow, but I might try this.

 

Stokestack, not to worry. Ideally, the bottom thread of your spark plug should be level with the bottom threads in your head. But in most cases a little difference won't hurt you. Our 363 turboed 67 fastback coughed out a plug so our machinist filled the plug hole and retaped it. No problems yet at 1100 rear wheel horsepower.
Just a reminder, NEVER remove spark plugs when ALUMINUM heads are still hot. I try to wait, if possible, for the heads to be cold.
Also, ALWAYS apply a THIN coating of "anti seize" only half way up the spark plug, ie. don't goo the anti-seize all over the threads, it can actually ground out the plug.
Finally, if you want to get crazy, like me, apply a thin coating of "dielectric grease" to your plugs insulator after installation. This helps you from pulling your spark plug wire out of its socket. Like your COBRA my HEMIs used the same system.
You have great heads, take good care of them.

 

Hey, thanks Buck.

I did put anti-seize on the plugs. Probably a bit more than you're recommending, but I was careful not to goop it all over the place.

Good idea about the grease on the top of the plug; I'll try to remember that next time.