I broke a coil bolt off in the head.... - Chevy Colorado & GMC Canyon
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post #1 of 8 (permalink) Old 02-21-2017, 08:13 AM Thread Starter
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Join Date: Nov 2016
Location: KY
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I broke a coil bolt off in the head....

Tell me it can be saved and I don't have to buy a new head. lol Here's what's happened..

2 months ago I posted about a random misfire I'd been having. I checked the coils first thing and all seemed normal. From there, I re-did all the grounds on the splice packs and under the seats and nothing. Figured I'd recheck the coils and when I got to Cylinder 3, the bolt snapped under very little torque.
I can put the coil back in and start it up and it'll miss until I press on the coil and then it runs great so I'm 99% sure this has been the problem the whole time.

I started by trying to drill a pilot hole in the original bolt to use a screw extractor and get it out but I got off center and it's been all downhill from there. I've tried tread inserts, all of which become loose once the motor heats up and thus, the misfire begins.

Can I put some JB weld around the insert? Can I use the lock-tite tread maker stuff? The hole is now about 2 sizes oversized and I refuse to drill anymore on this head. The side of the head has already chipped a little from getting to close to the wall but it's not cracking or anything.

I know it'll be expensive but I think it'd be cheaper to replace the head vs. buying a new vehicle (plus, this was my dad's and I really don't want to part w/it.) Couple guys on another site said if you replaced the head on our trucks to replace it with one from a 07 3.7 engine?

TL;DR: I fudged up the coil bolt hole on Cyl3, tread inserts won't stay in, any option besides buying a new head?
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post #2 of 8 (permalink) Old 02-21-2017, 09:10 AM
Join Date: Dec 2016
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Take it to a mechanic. Thread inserts work well if they're done properly.

If you've already drilled out the broken bolt two sizes over, then you probably drilled out the threads as well. That is a problem, but you might be able to now re-tap the hole and install an insert. It all depends on how large that hole is now and whether the head is compromised by you drilling too close to the wall.

- Anthony

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post #3 of 8 (permalink) Old 02-21-2017, 09:13 AM
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I had a glow plug stripped out in my 6.2 once.

What the mechanic did was put in a thread insert, and then he used a compound that he used to put in valve inserts in, and put anti-seize on the plug threads. He told me not to remove the glow plug until the engine had been driven for awhile, since the heat is what would cure the compound that he used.

So, in this case, I would think that using JB weld on the thread insert would work just fine. I would use the 24 hour cure though, since I think that stands up to higher temperature.
You may want to check that though, what the heat range is.

Another thing, get yourself a set of reverse drill bits. Many times, when I had to do this, the act of drilling with the reverse set would remove the bolt 90% of the time.

I would recommend using the valve insert compound, but I don't know what the name of that is. Just know that it could easily withstand the temperature range of the head.

2016 Colorado LT, Laser Blue,CC,4WD,2.8L diesel, ARE Topper

Last edited by Marty G; 02-21-2017 at 09:15 AM. Reason: add information
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post #4 of 8 (permalink) Old 02-21-2017, 09:49 AM Thread Starter
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I had some JB in the cart at walmart last night but the more I thought of it the more I didn't want to waste money on something I didn't know for sure would work. But I remember checking the heat range on the back and it was something like 500F. Idk if it gets that hot at that hole or not. I wouldn't think so but idk.
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post #5 of 8 (permalink) Old 02-21-2017, 10:20 AM
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JB Weld costs what, $5? How would you not spend $5 and see if it worked?

This is a simple issue to advise on. Hole is now two sizes too big. You are going to have to using a tap to cut new threads and then use a helicoil with the threads you need, however, you may not find one that has an OD that is 2x over with an ID that fits your bolt. I'm not sure.

- Anthony

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post #6 of 8 (permalink) Old 02-21-2017, 10:44 AM
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post #7 of 8 (permalink) Old 02-21-2017, 02:36 PM
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You're not talking about a high stress or high torque bolt here. So you don't need to step up to something like a Time-Sert.

Clean the hole really well with brake cleaner, and blow it dry with compressed air. Fill the hole with JB weld. Not the stick kid, but the kind you have to mix up like body putty. Make sure it's full, with no air bubbles.

Let it cure completely, and then a little more. Now you can drill and tap a new hole. You could even drill it for a thread repair kit, and put steel threads back in there.

2016 Colorado: long bed, Z71, Mini-Duramax
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post #8 of 8 (permalink) Old 02-21-2017, 03:41 PM
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Helicoils work well

BUT, i'd try a left handed drill bit first!!!!!!!!!!!!!!!!!! Sometimes it backs um right out. Not too much speed on the drill or you will break or burn out the bit.

I use to be machinist. This works!!!!
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