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Stripped bolts

So my 2006 Mustang GT came back from the shop, where they said they’d checked spark plugs and found the bottom of the wells very greasy. Last weekend, I pulled off the coils and the boots and cleaned it out. That’s when I noticed that all but two of the threads in the housing for the coil retaining bolts had been stripped or nearly so (Thank you very much Ford dealership! Though, to be fair, I’d notice that, despite tightening them finger tight when I’d removed them to change the plugs months ago, they were already showing some give.).
So, a couple of/three questions:

  1. Am I right in thinking that these bolts, the ones retaining the coil, are 10-32s in diameter/thread count?
  2. Has anybody repaired their stripped threads using inserts, and how’d that turn out?
  3. Any other recommended methods of repair?

A thread insert works great as long as there’s access to the stripped hole with a drill, and where the tap can be used and the insert installed.

As far as the tread size? Take one of mounting screws to a local hardware store and find a nut that threads on. That’s the thread size.

You want to get the proper size thread insert. Because these thread insert kits aren’t cheap.


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Good suggestion. All the hardware stores I go to have thread gages right at the screw/bolt counters. They’re usually a full set of metric bolts & threaded holes all arranged along with a full (separate) set of SAE.

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Already done, Tester. I’m just trying to make as sure as I possibly can about the thread size. Because, as you say, the insert kits ain’t cheap! So I was hoping someone knew the specs for those bolts on my model/year car.

Beyond the good advice above, suggest to keep on this until it is fixed correctly. The coils likely have to be attached soundly to where they mate with the mounting bracket for both grounding and heat sink reasons. You don’t want misfires to start, as it could damage the cat. I had a sort of similar problem recently on my truck with the starter motor solenoid; it had come loose from its moorings due to stripped threads on the sheet metal screws holding it in place, and this was preventing the engine from cranking, due I presume to the lack of a ground.

I looked up those bolts on Mitchell’s.

And all they provide is the torque spec.

Nothing about the thread size.


What size socket did you use to remove the bolts?

That’ll sometimes provide a clue to the thread size.


If it was my car, I would use a “cheapskate” fix I have used many times over the years. Find some longer bolts or threader rod the same size and a flat washer and nut for each bolt.

Cut the heads off the bolts and thread these studs finger tight into the hole. Make sure the bolts stick up enough to go through whatever you want to attach and that there is enough clearance for the nut and washer.

Remove the studs and turn them around so the cut portion of the threads is going to go down in the hole. Mix up some JB Weld or your favorite epoxy, use a toothpick to put a little down in the hole and coat the bottom half of the threads on the stud. Insert the stud, screw it down, and let cure overnight.

I used this a lot when my kids and I were buying ols worn out Chrysler products with aluminum case Torqueflite transmissions. The trans pans usually had about half the bolts stripped. If the holes were too big to grip the bolts at all, I would add a thin rope of steel wool to the hole.

I can tell you they ARE metric, not 10-32 English but it really doesn’t matter IF you change the bolts, too. It just confuses the next mechanic that services the coils. The Ford Mod motors are all metric. Thread inserts are a little tough to use on blind holes since they usually don’t include bottoming taps for the inserts. Be careful you don’t break through.

I like @oldtimer_11 's fix but I suggest you use metric all-thread which is available from McMaster Carr or Grainger. It is generally hard to find locally.

Hey, oldtimer_11. I thought of that! It’s good to get some validation to my thinking. But, without getting into complicated descriptions, suffice it to say that it won’t work on my car, because of the shape and placement of the bolthole.

Hey, Tester and y’all!
So I cleaned out the facing of the bolt head, as I could see some writing engraved there. It turned out to read “8.8”. It took a while, but I found out on the 'net that was the marking for a 5 mm thread. So I ordered the thread inserts already.
Now, follow-up question: The inserts are much shorter than the length of the bolt hole. Has anyone attempted using several inserts on top of each other to lengthen the depth of a thread? It seems to me that it would be hit or miss for the threads to align correctly from one insert to another, but would be great if somehow they did.

8.8 is an indication of the strength of a metric bolt, not a size.

Don’t install 2 inserts. They won’t line up. One insert is all you need since it is much stronger than the aluminum.

make sure you clean your bolt hole.

always clean your bolt hole thoroughly. always.

old_timer 's post above is correct. An “8.8” marking on the head of a bolt doesn’t define the bolt’s dimensions or thread pitch. It defines its material properties, yield strength, tensile strength, etc. “8.8” does confirm it is a metric bolt I think. Perhaps that’s how you made the sizedetermination, you knew the appx size, just didn’t know if it was metric or US. See the link below for a better explanation.

The rest of you probably don’t agree but I’m a little skeptical of this fix myself. It’s pretty easy to go down to the hardware store and check to see what size the bolt is. I had one that didn’t fit either standard metric or SAE but a little research got me the correct tap on line. I’m still not sure why it can’t just be tapped out to the next size up rather than all the trouble with the insert and now probably the wrong one. Maybe thread restore wouldn’t take the heat but I’m just not feeling positive about this approach.

The treads in this aluminum valve are probably gone, no chance to straighten them with a tap.

Helicoil inserts are cheap and available in different lengths, the standard length commonly available should be more than adequate for an ignition coil.

Whether you go a size larger with the hole or install an insert it is only 5 minutes per hole, no big deal.