Unfortunately helicoil isn't going to be an option. I done goofed it up real good. Who let me have access to power tools anyway???
I did finally get the EZ out, well... out, by eating away at it with a (multiple) diamond coated Dremel bits. After it was removed, I got to work drilling.
I started with a bit that was about the same size as the inside thread diameter of the glow plug. Although I was able to drill down a little past the threaded section, I was not able to pick out what was left of the glow plug threads. I believe they got married to the sides of the hole at some point during my welding adventures.
So then I went with a 13/32 bit cause I believe that is damn close to the correct size to use with a 10x1.0mm helicoil. So after completely drilling out the threads, I was able to remove what was left of the glow plug. With the tip still attached! So that's the good news.
The bad news is that at some point during my drilling adventures, I put a bad angle on the hole. See the crappy illustration below.
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So it was close enough for me to remove what was left of the glow plug, but not close enough for me to insert a new one with a helicol. It gets bound up, and I'm sure if I were to get it tapped with a helicoil and somehow managed to get the plug back in, that the glow plug shoulder would not seal properly with the head.
Luckily, I guess if anything here could be considered luck, I didn't mangle the entire hole. The 1/4 - 3/8 of an inch that's below the glow plug threads is still intact.
Oh and with no worries about having a glow plug tip rattling around in the combustion chamber, I went ahead and compression tested the other cylinders. Got between 400 and 450 on all of them, so I got that going for me.
Anyway, unless anyone has a better idea, here is my plan to fix this awful mess and hopefully still have a functional glow plug in cylinder 6.
1. Use a Dremel or similar to eat away at the top of the hole just enough so one of the old glow plugs will fit in.
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2. Insert an old glow plug so it sits in the part I haven't screwed with.
3. Take a diamond or carbide hole saw that just fits around the glow plug and use it to widen the hole with the glow plug as a guide. I have a diamond one that is nominally 1/2. Should make a hole around 0.52 Hopefully this will make the new even larger hole square so the glow plug will seat and seal properly.
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4. Tap the new larger hole hopefully to 9/16-8. Or maybe 3/8 NPT if I wallow the hole out too much while going at it with the hole saw.
5. Thread in a bushing matching the outside diameter and thread pitch, already having the center drilled and taped to 10x1.0mm for the glow plug. I think I can use a 3/8x1/4 iron pipe reducer bushing for this with the hex head cut off, but I'm going tomorrow to see what I can dig up at the hardware store.
6. Compression test cylinder #6.
7. Hopefully the compression test will be okay and then I can reassemble with red thread lock or maybe JB Weld on the bushing and anti seize on the plug, and be done.
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I guess if that doesn't work, I'll be tapping and screwing in a length of threaded rod with plenty of thread sealant or JB Weld, and saying goodbye to #6 glow plug. Then I'll probably go have a long cry, or a lot of whiskey. Hell probably both! Before I do anything else with this truck. Longest "15 minute" job I've ever done.
