Author Topic: Exhaust Manifold Bolts  (Read 302 times)

Offline Jon87V20

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Exhaust Manifold Bolts
« on: February 08, 2018, 01:45:54 PM »
This weekend I’ll be replacing my factory exhaust manifolds on my ‘87 Suburban V20. The bolts are looking very rusty and I’m wondering if anyone has any advice for getting them out without breaking them.

Would it be helpful to drive it around until it’s hot? Should I use a torch? I hosed it down with PB Blaster last night as well.

Just really trying to avoid breaking these off!

Thanks,

1987 Chevrolet Suburban V20 Silverado
350ci TBI TH400 NP208

Offline VileZambonie

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Re: Exhaust Manifold Bolts
« Reply #1 on: February 08, 2018, 06:37:11 PM »
Hotter is better and if they feel like they're going to break, they are going to break. It may be inevitable but if they do then be prepared to heat and spin out the leftovers. If they break close to the head you can always weld a nut to the remainder of the bolt to run them out. Worst case, drill and tap.
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Offline FlatBlack77

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Re: Exhaust Manifold Bolts
« Reply #2 on: February 08, 2018, 07:47:38 PM »
go a little loose then a little tight do that a few times and see if they feel like they are going to come out easily. if not then fire it up and and get it hot as you try and work them back and forth.

but like Vile said, if they are going to break they are going to break
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Offline Irish_Alley

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Re: Exhaust Manifold Bolts
« Reply #3 on: February 09, 2018, 09:01:27 AM »
also if you heat up the bolt it will expand and might expand to the point where its bigger than the hole its trying to get out of. you have to try and heat the bolt and manifold the same but too much you will weaken the bolt causing it to twist and then snap.

it might be better to expect them all the break and if they dont come out at first then try and cutting the heads of the bolts of to remove the manifolds then once the manifolds are off weld nuts to the "studs" you have and then try heating just the heads. that way your not working with a bolt thats broke off flush in the head
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Offline VileZambonie

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Re: Exhaust Manifold Bolts
« Reply #4 on: February 09, 2018, 05:16:34 PM »
The bolt will melt before that happens. With heat dissipation and different thermal expansion rates, the two dissimilar metals once again become two separate entities. The intense heat helps make coarse material become fluid so that the threads can once again operate and that is why you heat the bolt.
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Offline Irish_Alley

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Re: Exhaust Manifold Bolts
« Reply #5 on: February 10, 2018, 09:08:21 AM »
when i have or seen others heat bolts or nuts its generally with an oxy acetylene torch. they can reach temps around 6k°F. generally speaking we would heat the bolt/metal till cherry red then try to remove.

the manifold bolts are long so you have to heat the head a little more and have the heat travel to the threads which wont be equal amount of heat on the head vs the threads. so when you heat the bolt head just to see "red" your heating the bolt to about 1k°F just to get it red and cherry red is 1.5k°F+ orange is around 1.7k°F. bolts tend to start dropping their strength around 750°F so anything above that will weaken them. so yes if you get the head just red the shaft near the head will be the weakest point while the threads wont be red at all and should not really be affected by the heat anyway making it almost pointless to heat just the head. then you will have the manifold absorbing some heat from the shaft of the bolt and taking more away from the threads of the bolt.


 i can agree that the manifold and bolt will become separate entities and im going to also add this, the thermal properties of manifold bolts is a little different than lets say a grade 5 or 8 bolt so my opinion might totally be wrong

img from https://www.hearth.com/talk/wiki/know-temperature-when-metal-glows-red/

"What are the temperature limits of Grade 5 and Grade 8 bolts?
Grade 5 and Grade 8 bolts should not be exposed to temperatures above 450°F or below -50°F. Expect a reduction in yield strength at elevated temperatures." (https://www.fastenal.com/en/82/engineering-faq)
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Offline Jon87V20

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Re: Exhaust Manifold Bolts
« Reply #6 on: February 10, 2018, 03:26:49 PM »
So none of them broke! I just pulled off the driver’s side manifold and there’s no gasket in there. Is that normal? Gaskets came with the new ones. Should I not put them in there?
1987 Chevrolet Suburban V20 Silverado
350ci TBI TH400 NP208

Offline VileZambonie

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Re: Exhaust Manifold Bolts
« Reply #7 on: February 11, 2018, 08:33:39 AM »
Glad to hear you got them out without incident. Yes run the gaskets and yes it was normal that they were installed without them when new.
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Offline Jon87V20

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Re: Exhaust Manifold Bolts
« Reply #8 on: February 11, 2018, 03:57:28 PM »
So now I’m in kind of a tough spot. I got the driver’s side manifold on and bolted up and now the flange on the exhaust pipe is too small to fit on the new studs... Not sure why, it’s out of another Suburban I found in the junkyard. Is it possible they shrunk somehow because I was using through bolts with the old manifolds?

I tried drilling the holes out bigger on the flange with a 1/2” drill bit and it’s still not fitting. I tried to put the old manifolds back on and they both shrunk slightly and now I can’t bolt them back on. I didn’t think that would happen since the engine was completely cold (sat overnight) when they were removed.

Should I go buy a bigger drill bit? There’s isn’t a whole lot of material left outside the holes as it is. Totally bummed right now. It seemed like a miracle none of the bolts broke but now things aren’t fitting.

The only reason I went with factory manifolds is because I didn’t want to change all the piping right now. Otherwise, I would have just bought headers for it.

Now that the old manifolds have shrunk, does that mean they’re no good now? Is there any chance they will fit back on somehow?

Thanks, guys.
« Last Edit: February 11, 2018, 04:20:36 PM by Jon87V20 »
1987 Chevrolet Suburban V20 Silverado
350ci TBI TH400 NP208

Offline Irish_Alley

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Re: Exhaust Manifold Bolts
« Reply #9 on: February 11, 2018, 04:32:47 PM »
They make a tool for exhaust manifolds to expand them
If you can’t tell yourself the truth, who can you tell it to?~Irish_Alley

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Offline Irish_Alley

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Offline VileZambonie

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Re: Exhaust Manifold Bolts
« Reply #11 on: February 11, 2018, 05:33:02 PM »
All you have to do to make the studs move a little is put a deep socket over them with a long extension and slightly bend them into position but it sounds like you're way past that point. Why not get new manifolds?
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Offline Jon87V20

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Re: Exhaust Manifold Bolts
« Reply #12 on: February 11, 2018, 06:16:57 PM »
Vile, what happened was, I bought new manifolds and had the driver’s side new one bolted up to the head with no issues. The snag was down where the manifold meets up with the pipe. The triangle flange bolt holes are slightly closer together than the studs coming off the manifold.

I need to use the truck tomorrow so I thought I could just throw the old manifolds back on for now until I figure out what to do. However, now the old ones aren’t fitting because they shrank while they were off. Now I don’t really know what to do other than go buy a bigger drill bit and try to drill out the holes on the flange until they fit. I’m just concerned there’s not much material left before it breaks through to the outside edge. Does that matter if the edges of the flange are just open, or will that cause issues with the donut gasket sealing properly?

Also, would you advise against heating the studs and trying to bend them inward closer together?
« Last Edit: February 11, 2018, 06:20:13 PM by Jon87V20 »
1987 Chevrolet Suburban V20 Silverado
350ci TBI TH400 NP208

Offline VileZambonie

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Re: Exhaust Manifold Bolts
« Reply #13 on: February 12, 2018, 05:59:33 PM »
Without seeing what you mean I am not willing to give bad advice. As far spreading the manifold just get one of these
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Offline Jon87V20

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Re: Exhaust Manifold Bolts
« Reply #14 on: February 16, 2018, 06:50:08 PM »
So I have it all done and everything was going fine until this plug on the front of the manifold blew out and it started leaking out of that. Does anyone know what size this thing is?! 3/4" is too small. Maybe 7/8"? I measured the bore of the hole and it measure 3/4" but the bolt I bought was 3/4" and is too small to where I can just drop it in with about a millimeter or two of space between the bolt and the hole. Is this thing metric maybe?
1987 Chevrolet Suburban V20 Silverado
350ci TBI TH400 NP208