Need Help With Stripped Coil Pack Retaining Bolt Insert

goose814

Original poster
Member
Mar 29, 2014
4
I have a 2003 Trailblazer EXT with 209,000 miles on it. I have changed the plugs twice every 100,000 miles with no problems. The other day it started running rough and was getting a flashing "Check Engine Soon" light. I ended up finding the #6 coil pack not seated on the plug because the hole for the retaining bolt is stripped out.

I assume the retaining bolt threads into the head. Can anyone tell me if there is an insert or helicoil that goes into it or is the head actually threaded. If anyone can help with any other solutions, it is greatly appreciated.
 

The_Roadie

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Member
Nov 19, 2011
9,957
Portland, OR
Pretty sure it's a straight threaded hole, and a helicoil is the right thing to do. I do almost everything myself, but I have a favorite independent mechanic I let do my helicoil work. The torque spec on those bolts it tiny, and a lot of folks break them. Mostly don't hear about strippage, though.
 

The_Roadie

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Nov 19, 2011
9,957
Portland, OR
I think JB Weld would be useful. Loctite not so much if the bolt doesn't catch on any of the stripped threads. A fabbed-up retention strap across the coil might also work - it doesn't have to be tight - it just has to prevent the coil from hopping off the spark plug and that might allow 1-2 mm of looseness without problems.
 

gmcman

Member
Dec 12, 2011
4,656
Worst case you could pull the intake then the valve cover and repair the damaged threads. Just be careful about the metal shavings in the valve train.

Since the threads are toast, I would try a similar bolt with coarser threads and just snug it down to seal the gasket. I would personally leave the JB out of the equation as of now just to reduce the risk of damaging the bolt hole or snapping those fragile OE bolts.
 

AbsoluteZero

Member
Nov 21, 2011
211
What I proposed would replace the existing hold down bolt with a stud. The stud wouldn't turn. A nut would be used to hold down the coil.

This is a simulated pix using a 1/4-20 bolt. It's been some time since I changed plugs so don't recall sizes.
 

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gmcman

Member
Dec 12, 2011
4,656
I would try one size larger in metric before the JB weld, considering it's the cyl head you are fastening to. Just my $.02
 

KimV

Member
Apr 23, 2016
3
Texas
Ok. Hoping someone is still watching this thread. Broke the #6 coil. Currently trying ez out but it went in more on the side so most likely won't wotk..what I'm thinking is to rethread the hole, use 2 aided screw to screw into hole then coil would go over that and use bolt on top to hold..will that work? Seems like the coil itself has threads.

Any help appreciated..I don't work on cars but stupidly thought how hard can changing spark plugs be...ugh
 

Sparky

Member
Dec 4, 2011
12,927
Sorry I'm not quite understanding what you're trying to do. So the bolt broke off in the head? What are you rethreading if the bolt won't come out (or did you already get it out)?
 

KimV

Member
Apr 23, 2016
3
Texas
Actually now I've just made a mess. The coil pack screw broke off. Have been working for several days to get it out...I am giving up...also spark plug is still not straight so coil won't sit right..have to find anew honest mechanic..don't really want to go to the dealer.
 

mrrsm

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Oct 22, 2015
7,639
Tampa Bay Area
Welcome to GMT Nation...

In a related Thread on Broken Exhaust Manifold and Head Bolt issues... @Sparky mentioned having success using a Small, Flat Blade Screw Driver to Coax the broken bolt remnant out of the hole(s). Another Member suggested using a Harbor Freight Pick Set to grab the gnarly edges of the bolt inside the hole and do the likewise with gently unwinding it and causing no damage to the remaining threads inside of the Aluminum Engine Head.

The important thing to remember is that after the top of the bolt snaps off... there is no longer any tightening tension in between the bolt threads and the thread lines cut inside the head receptacle. If Counter-Drilling is tried, it must be done after Center-Punching DEAD CENTER on the bolt face inside a tiny hole that measures only M6X1.0 in thread dimensions... so you would have to be VERY careful not to allow the Split Drill Flutes to wander off into the adjacent aluminum head ...and make matters worse.

A while back... I did a Complete Write Up and Pictorial on the Best Way to Do This Broken Ignition Coil Fastener Repair:

 
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