Topic: Broken Exhaust Manifold Bolt (Suburban)
in Forum: Non-Vette Automotive Discussion
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So this weekend I decided to upgrade the RH exhaust manifold on my Suburban ('91, 350, TBI) from the stock "3-piece" design to the more modern and effective "single piece" style. (I knew about one of the cracks but not about the one underneath the heat stove!) Other than having to break all three bolts on the exhaust pipe end (no biggie) no problems getting the old one off.
But when I installed the new one I must have gotten the 5th bolt from the front cross threaded and it broke off. I was re-using the old bolts. It went in smooth at first but I got to the point where it became too hard to torque and by then it was too late - required as much torque to back out as it did to go in. Good news is I have about 3/4" of threads sticking out - but what to do with them?? So far all I've tried is the two nut method - locking the first nut on with a second nut -- to no avail. Other ideas that don't require drilling down there or welding? I know it's probably a no-go, but what about leaving it as-is? Will that port not seal? The plan is to eventually upgrade the cylinder heads on that motor, but was hoping to not do that immediately! Any thoughts or tricks would be greatly appreciated, thanks.
1976 Silver/Firethorn. L48, 4spd. Original 2 bolt, vortec heads, 9.4:1 CR, Speed Pro Cam: 224/224@0.050, 112 LSA, Eagle Steel Crank.
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Vette(s): #1-1974 L-48 4spd Cp Med Red Metallic/Black deluxe int w/AC/tilt/tele./p/w-p/b/
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GM # 1052627 Heat Riser Lube & Rust Penetrant.
GM rust penetrant and inhibitor heat valve lubricant AC/Delco #10-4020 88862628
Both pretty much the same thing, should be available at any GM dealer. Soak that puppy down for a day or so, then first try to tighten the broken bolt a little before loosening. Work it back/forth a little at a time, but not continuously....you'll wind up twisting what is left off in the head. Just a little twist one way, the back the other, then let it sit for a few minutes. Repeat as needed. IF it does break off, the only option is to drill it out. You can install the manifold without the one bolt, but....it will burn thru the gasket soon, if not immediately, and you'll be right back where ya started....with a wicked exhaust leak...
|UPDATED|8/18/2014 9:43:21 AM (AZT)|/UPDATED|
GM rust penetrant and inhibitor heat valve lubricant AC/Delco #10-4020 88862628
Both pretty much the same thing, should be available at any GM dealer. Soak that puppy down for a day or so, then first try to tighten the broken bolt a little before loosening. Work it back/forth a little at a time, but not continuously....you'll wind up twisting what is left off in the head. Just a little twist one way, the back the other, then let it sit for a few minutes. Repeat as needed. IF it does break off, the only option is to drill it out. You can install the manifold without the one bolt, but....it will burn thru the gasket soon, if not immediately, and you'll be right back where ya started....with a wicked exhaust leak...
|UPDATED|8/18/2014 9:43:21 AM (AZT)|/UPDATED|
Joel Adams
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If the penetrating oil doesn't work see if one of your friends has a portable mig welder. This is a little trick I do to remove broken exhaust manifold bolts on Ford trucks and Chevy trucks with the LS style engines.
I take a nut that will just slip over the broken piece of the bolt. I slip it on about halfway leaving a couple threads of the nut exposed. Then carefully weld the center of the broken bolt to the center of the nut. Then while its hot I try wrenching the bolt out. It may take a few times due to the nut twisting off sometimes. But I've had success with his method.
Good Luck!
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Thanks, guys. Joel, what method of turning are you recommending? Continue trying with the double nut method? Is there a type of locknut that I can use as the outside nut that would lock better? A guy at work is suggesting to grind off two sides of the exposed bolt that would allow use of an open end wrench. Thoughts?
Sarge - definitely going to keep my options open regarding welding. Already talking to someone at work that has a portable MIG. Thanks!
1976 Silver/Firethorn. L48, 4spd. Original 2 bolt, vortec heads, 9.4:1 CR, Speed Pro Cam: 224/224@0.050, 112 LSA, Eagle Steel Crank.
would it work to stake the threads with a cold chisel to prevent the nut from backing off? Instead of using a second nut which hasn't been working too well....
1976 Silver/Firethorn. L48, 4spd. Original 2 bolt, vortec heads, 9.4:1 CR, Speed Pro Cam: 224/224@0.050, 112 LSA, Eagle Steel Crank.
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Vette(s): #1-1974 L-48 4spd Cp Med Red Metallic/Black deluxe int w/AC/tilt/tele./p/w-p/b/
Am-Fm/map light National/Regional/Chapter NCRS "Top Flight"
#2-1985 Bright Red/Carmine Cp.L-98/auto
Member: NCRS, NCRS Texas, Corvette Legends of Texas
If the double nut thing ain't werkin, you might also add the peening of the end of the bolt to help hold the nuts on better. Just wondering if you have enough room to get a hammer down in there....
Doubt that grinding flats on the bolt will work....you'd only be making an already unstable fastener more unstable....it's prolly snap right off.
Don't s'pose you have room to use an impact wrench on it.....and have an impact wrench available?
Got enough room to add a third nut? I know...prolly not, but just thinkin out loud here....
Doubt that grinding flats on the bolt will work....you'd only be making an already unstable fastener more unstable....it's prolly snap right off.
Don't s'pose you have room to use an impact wrench on it.....and have an impact wrench available?
Got enough room to add a third nut? I know...prolly not, but just thinkin out loud here....
Joel Adams
C3VR Lifetime Member #56
My Link
(click for Texas-sized view!) NCRS
"Money can't buy happiness -- but somehow it's more comforting to cry in a CORVETTE than in a Kia"
Got it off! 
PB Blaster and double nut method next day worked great. I used a full size nut as the first nut and then a half size jam nut as the second. Torqued the second against the first pretty good. Then used an offset box end wrench and walked it out. End of the bolt was pretty boogered up, but I ran a different bolt in w/o the manifold on and it went in all the way smooth and came out easy. Not sure what exactly happened, but I'm just glad I should be able to get it back together now. Thanks for the help!
PB Blaster and double nut method next day worked great. I used a full size nut as the first nut and then a half size jam nut as the second. Torqued the second against the first pretty good. Then used an offset box end wrench and walked it out. End of the bolt was pretty boogered up, but I ran a different bolt in w/o the manifold on and it went in all the way smooth and came out easy. Not sure what exactly happened, but I'm just glad I should be able to get it back together now. Thanks for the help! 1976 Silver/Firethorn. L48, 4spd. Original 2 bolt, vortec heads, 9.4:1 CR, Speed Pro Cam: 224/224@0.050, 112 LSA, Eagle Steel Crank.
Lifetime MemberModerator
Duncanville, TX - USA
Joined: 11/8/2003
Posts: 20214
Vette(s): #1-1974 L-48 4spd Cp Med Red Metallic/Black deluxe int w/AC/tilt/tele./p/w-p/b/
Am-Fm/map light National/Regional/Chapter NCRS "Top Flight"
#2-1985 Bright Red/Carmine Cp.L-98/auto
Member: NCRS, NCRS Texas, Corvette Legends of Texas
Joel Adams
C3VR Lifetime Member #56
My Link
(click for Texas-sized view!) NCRS
"Money can't buy happiness -- but somehow it's more comforting to cry in a CORVETTE than in a Kia"
in Forum: Non-Vette Automotive Discussion
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