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2004 gmc
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26,181 Posts
Discussion Starter #1
Only 55,000 miles, but I think it cracked from a dose of cold water when I went through 18-20" Coyote Creek a couple of weekends ago in the desert with Only1Balto. Sigh...

So I took it off today. Even if I pay my trusted independent GM mechanic to put it back on, I was curious. Maybe too curious.

Yep. big fat crack:







Looking pretty empty in here:



Far rear:



Oops.



Final tally of siezed and torqued off manifold bolts in the head = 3.

:duh: :hissy: :ugh: :sadcry: :sadcry: :sadcry: :sadcry:

Of 11 bolts (8mmX1.25), the ones that broke are the farthest forward and the two farthest rearward. Almost impossible to see without a mirror. I even took off the power steering pump to see if the access got any better - still miserable. Even with a very short right angle drill, I have very little hope that anybody could get a screw extractor in there straight.

So - what's the betting that there's no way to fix this except remove the head and take it to a shop? I could drill and put in helicoils in the machine shop at work, but I'm really not looking forward to removing the head working in the dark after work every night. So I'll probably tow it to the mechanic tomorrow, take my lumps from him for being a dumb butt, and open my wallet. Sigh... :)

 

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Northwest Chapter
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11,824 Posts
Sorry to hear its cracked, but that really sucks about the bolts. Seems this happens a lot when pulling the manifolds for the I6s.:(

Im going to pull the shield on my 02 when I get home and check it, too many of these failing to not spend the couple hours to make sure its ok IMO.
 

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2002 chevy trailblazer_ltz
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236 Posts
Just curious here, but is there some tell-tale signs of a cracked manifold? Typical exhaust leak-sounds perhaps?
 

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2004 gmc
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26,181 Posts
Discussion Starter #4
Mine sounded like an unmuffled Harley for the first 2-3 miles, then the noise got softer until it was only about twice as loud as the Flowmaster 70 exhaust. I concluded it was an manifold crack rather than a exhaust gasket problem because it got quieter as it warmed up.
 

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2006 chevy trailblazer_lt
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1,055 Posts
Hey sorry to see this Roadie, really sucks. Its too bad it wasn't only 1 bolt. When I exchanged my manifold for an Extrude-Honed and ceramic coated one on the blue Trailblazer, I was left with 1 bolt in the head. My mechanic said he thought it would be fine, and 3 years later, it still was.

But 3, definitely a problem. Hope all goes well ...

AG
 

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2004 gmc
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26,181 Posts
Discussion Starter #6
Yah. After the FIRST one I was horrified that it would take so little torque to break one. So I was using less torque than that when the others broke. They are delicate things, and you install them with only 20 foot-pounds of torque. But these are 8mm, and they were breaking with torque that a 1/4-20 screw should have withstood. There is some sort of high-temp loctite applied, not anti-sieze, per the factory manual, so that must be the difference. I feel like such an amateur wrench tonight. :worried:
 

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2004 chevy trailblazer_lt
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201 Posts
Dang dude that sucks. Now I am scared about trying to change my cracked manifold. Any tips to prevent me from breaking bolts off?
 

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2004 gmc
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26,181 Posts
Discussion Starter #8
The torque is relatively high on the bolts all the way out probably because of this high temp thread locker they use. Probably due to casting variations, the bolt holes in the manifold are much larger than the bolt, which has a large flange to act as a washer. Because the manifold hole isn't the same size as the bolt, any side force on the bolt head can bend the bolt from side to side. Because of the position of the bolts, I was using a deep socket and a short extension, and thinking back on it I wasn't being absolutely careful to keep the socket in line with the bolt. This could be my problem. I would recommend using a u-joint right on top of a short socket, then an extension. The u-joint would relieve that sideways stress.

I don't think penetrating oil would have helped because of the thread locker, which was mentioned in the Helm manual.
 

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2002 chevy trailblazer_ls
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2,217 Posts
I guess there's no room or way to get on each of the bolts with a socket and give each one a few taps with a mallet straight on to help loosen them up first? That's about the only thing I can think of that might work and not break bolts.

Pulling the head is not an easy task at all. A friend's here locally has a head gasket leak and we've studied pulling the head. You need some special tools to hold the cams and timing chain in place otherwise if you drop the chain you then will have to pull off the front cover and to do that you have to pull the bottom pan off the engine, all to retime the chain.... major disassembly!
 

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2004 gmc
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Discussion Starter #11
Update

Art (my aftermarket GM mechanic - not Al the bumper guy) got one of the three broken ones out today, after a lot of penetrating oil soakage and patience. The second one is drilled out, but bends the screw extractor when he applies torque. With another night of penetrating oil, this one should come out. The last one might respond to the same patient treatment.

His best idea to pass on to you guys is to treat the bolts as taps in reverse when taking them out. After a couple of turns OUT when the torque goes up, run the bolt IN a few turns to ungunk the thread locker from the threads. It might be a build-up of thread locker residue trying to remove the bolts all at once that's the problem. I can see that. Reversing a tap is the way you HAVE to use to break off the chips, so this makes sense. Might work for you lucky enough to come after me.

So I might save the expense of a head pull. More later. I've rented a Toyota Highlander for a long weekend drive to Prescott, AX at 5000 feet elevation. Might snow. I'll try not to fall in love with the Highlander.
 

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2004 chevy
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191 Posts
Broken exhaust manifold bolts in an aluminum cylinder head are a pain! I had to drill out 4 bolts from a dodge neon cylinder head on my cousin's car using a low speed right angle air drill and a mirror. I can feel your pain.

Has anyone with this problem used heat to try to soften the thread locker? Most common high temp thread lockers require heat to reduce the break-loose torque for disassembly. I can't find it right now, but I know I have the break-loose torque vs temperature curves for Loctite 266 and 272 sitting in my office somewhere.
 

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2004 gmc
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Discussion Starter #13
Those are exactly the tools Art's using. After reading DIRE warnings about only removing spark plugs when cold, and I swapped spark plugs just before working on the manifold, I was gun shy about adding any heat. Also there are warnings about welding stuff on the ends of a broken stud (if it stuck out, which mine didn't) in an aluminum head.

I didn't find a chart like you remembered for Loctite 266 or 272, but this footnote on their spec sheets: In rare instances where hand tools do not work because of excessive engagement length, apply localized heat to nut or bolt to approiximately 250 degrees C. Disassemble while hot. The chart you might be thinking of is strength while hot versus room temp strength.
 

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2002 chevy trailblazer_ls
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1,667 Posts
Sorry to hear of your troubles Roadie, no path has stopped you, so you'll get through this one. But hey, great pictures of that sort of thing. Too many people talk about stuff like this (cracked manifolds, blown trannys, broken fan clutches, cracked control arm welds, etc.) and don't provide pictures.

:thumbsup:Good job
and
:grouphug: good luck.
 

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2004 chevy
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191 Posts
I didn't find a chart like you remembered for Loctite 266 or 272, but this footnote on their spec sheets: In rare instances where hand tools do not work because of excessive engagement length, apply localized heat to nut or bolt to approiximately 250 degrees C. Disassemble while hot. The chart you might be thinking of is strength while hot versus room temp strength.
We went through the use of Loctite on some of our products and had to have recommended disassembly procedures for those components when disassembled in the field for repairs (I am a product engineer for ITT Goulds Pumps). We had the actual curves from Loctite that detailed the break loose torque as a function of heat applied from room temperature up to around 500 degrees F if I remember correctly.

And yeah, with internal aluminum threads, you have to be careful with the application of heat or you will strip the threads out of the head. You want to really localize the heat to the head of the bolt and let it conduct in through the threads. Well, at this point that would be quite difficult for you, but others needing to remove the exhaust manifold bolts for whatever reason may want to try some fast heat to the bolt head first before wrenching on them.

BTW, what are all of you guys with cracked exhaust manifolds doing with the old part? I may be interested in a junked one to use for dimensions for a possible home-made shorty header.
 

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2005 chevy trailblazer_lt_ext
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OK, Just tackled my 2005 Trailblazer.


All came out except 1. It is the rear one of the 3 in the middle (easy to get at)

Now I can't get at the exhaust flange. I have 3 extensions and still can't reach the freakin thing. I will wait til the neighbor comes home and borrow one from them

My questions now are... Do I put anything on the threads when I reinstall? Also what do I torque them at?


Thanks folks.:tiphat
'

P.S. That picture was awesome help.
 

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2004 gmc
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Discussion Starter #17
My questions now are... Do I put anything on the threads when I reinstall? Also what do I torque them at?
If you buy new bolts from GM, they come with pre-applied high temp threadlock compound. The shop manual says to use GM 12345493, but when I did mine, I didn't trust the original nuts enough to re-use them, and the new ones came with threadlocker applied so the mechanics can't mess up.

The torque process is three passes, done in that sequence from inside to outside, each pass done to 18 lb-ft. Exhaust pipe nuts are 37 lb-ft.
 

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I hate to have my first forum post be an "oh yeah, me too" but it is.

Had a Check Engine Light, code was Bank1 O2 Sensor.
Could not get O2 Sensor out with heat shield on, remove shield.
Cracked Manifold. Figures, Search on net, find forum, realize issues.
Get O2 Sensor out with pipe wrench, put in new O2 Sensor, order new parts.
Gmpartsdirect.com
Manifold - 88890560 - $133.65
Manifold Gasket - 88890561 - $9.02
Downpipe Dounut - 15167765 - $12.52
Shipping - $32.59
Total - $187.78

Now I will deal with bolt breakage as it happens. Lets hope at 107,000 miles they wont (who am I kidding?).

Let's hope this fixes the O2 Sensor issue, and the Check Engine Light goes off....

The real worry, is shift problems, after the light came on, if you accelerate in ANY gear, under WOT, it climbs to like 5k rpm, never shifts....if you back off the throttle it will shift. Replace what it indicates and move on.

Lets hope that fixes the problem, as the Computer is the problem not know what is going on (who am I kidding?).

Any ideas otherwise?
 

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2007 chevy trailblazer_ls
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166 Posts
head bolt I6

My friend who is a retired GM guy said to soak the bolts overnight in penetrating oil then , slowly try and loosen bolts, then tighten again, going back and forth (tighten) to loosen the bolt so it doesn't break.
Did you do a tranny service ? Good Luck with your Blazer. The reason I'm watching this is because my sister wants to buy a 2002 LTZ with 165K and it has a cracked manifold also. Tranny fluid has never been changed, and very worried about problems down the road. Other then that the TrailBlazer was a one owner, really clean vehilce. please tell the forum how you are making out. :thx
 
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