Hello all,
Since the information I found was fragmented at best, I figured I'd do a writeup on how I fixed my blown sparkplug with a Timesert kit. The 3rd cylinder back on the passenger side ejected it's plug within the last 10 miles of a 900 mile road trip, here's what I did to fix it:
You will probably hear about the Time Sert 5553 kit, which is made for Fords, but mostly what I've seen on their website is 2V stuff where the damaged thread is much closer to the surface of the head. I bought Time-serts 4412E kit, which is for the same thread and profile, but extended. I still had to get on the back of the tool with a wrench, the top of their tool was about even with where the coil cover would be. I got their PN 44186 inserts, which are the same ones included with the 5553 kit, and the 6020 sealer. This job is nerve wracking but relatively easy.
First off, I cleaned as much of the aluminum shavings out of the coil area as I could. Working slow and clean will be a recurring theme. Long 3/8 extension down the hole to watch the piston, 18mm socket on the crank, turn over until the piston is most of the way down on the powerstroke. To confirm that the valves were closed, I bent the tip of a spare dip stick at a 90 degree angle, stuck it through the sparkplug hole, and confirmed that I could catch the backside of the open exhaust valves in a different cylinder on that back, but that I couldn't catch an edge in the cylinder of interest. That bent dipstick would prove to be a surprisingly useful tool later on.
Next, I put grease in the flutes of the tap, dropped it into the hole, and started turning. The tap in the 4412E kit is dual sized, I think the first step is to catch any remaining threads and the second size is to create the threads for the insert. I found that 1.5 turns with the tap was enough to load up the grease with chips: remove the tap, clean the contaminated grease out of the flutes, put fresh grease in, and keep going. Surprisingly easy to find the thread again on restarts. Eventually, resistance will increase as the large threads do their work, and then it gets easy to turn once the large threads have gone through to the combustion chamber. Again, 1.5 turns between cleaning, I went more once and had to scrape extra chips out of the work area with the bent dipstick.
Once the tap is at full depth, make sure it's below the remnants of the seat with your bent dipstick or other long feeling instrument. Add grease to the teeth of the seat cutter, install over the tap, and push and turn. Once a turn, pull the seat cutter and shine a light down the hole to see if your new seat is clean and continuous all the way around, if not, more pressure and more rotations.
Once your threads are made and your seat looks good, it's time to clean everything up. Use the bent dipstick to remove any leftover chips, the grease makes them surprisingly easy to grab. Use a bottle brush or a paper towel on a screwdriver or something, soak in brakeclean or a degreaser of your choice, and clean the threads you've just made. Give the 6020 sealer it's best opportunity to not make you have to install the oversize kit in the future. Once your cleaning supplies are coming out clean, add some oil to the threads of the installer tool, run the insert on, add some 6020 sealer to the threads of the insert, and begin the threads carefully. As their instructions say, turning is easy going in, resistance increases as the tool is seating the insert, and then it gets easy again. Congrats, you're done. Remove the installer tool, clean everything up, install a fresh set of NGK 4177 gapped to .045 if you're Marty tuned, or Motorcraft gapped to [?] if you're stock. Install your new set of 8 coil packs (you really don't want 1 to be different), and enjoy your car.
I put this off out of dread for like 2 weeks until my other cars 4l60 lost 1st and 4th and I had to get to work the next day. Took me about 4 hours including prep and cleanup, I could probably do it in 2 hours now. Good luck, and I'm happy to answer any questions that I see.