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Discussion Starter · #1 ·
I just replaced four of the right hand exhaust manifold bolts on my '94 Caprice 4.3 V-8 with new grade 8 bolts; I ended up re-using the first and third studs because they are very specialized (and expensive dealer only item (for '94 only)). [As detailed in my thread about O2 sensor readings in closed/open loop, I couldn't get a rear-most broken bolt out and had to drill/dremel/tap it to 1/2" (VERY difficult/risky).]

Two years ago, I replaced some of the bolts in the left exhaust manifold with grade 5 bolts. The rear-most bolt had broken off and the easy-out method worked. I am debating if I should carefully replace the grade 5 bolts with new grade 8 bolts; even though there is some risk of the rear-most bolt breaking (it may be degraded some due to ~15K miles of thermal cycles) during removal.

I am thinking that grade 8 is the best for the exhaust manifolds. Can anyone confirm this? Please let me know.

Not only has one of my '94 Caprices had both rear-most bolts break off, but I just found that my '94 Caprice Wagon w/110K miles has the right manifold's rear-most bolt broken off. So, obviously, this is a 'high-fail' bolt position... and I want to have the best grade bolt in the rear-most positions for sure.

Thanks,
Kevin.
 

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Common practice is to replace the exhaust manifold bolts on '94 - '96 cars with Grade 8 hardware. They are hardened and will carry the highest tensile load, which seems to help them withstand the heat cycles the bolts are exposed to. I've never seen a stud break, and never replaced a stud on my cars. I do, however, loosen and retourque the studs when I replace the bolts.
 

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Go with the grade 8 bolts. I upgraded all the ones on my Caprice with grade 8 after noticing my RMW had 3 broken bolts. As you have already found out, it is much easier to upgrade them before they snap.
 

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Discussion Starter · #4 ·
Thanks.

Looks like I will replace the left side's grade 5 bolts with grade 8.
 

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Also make sure you cut the metal ribs between the center and outer exhaust ports on both manifolds, and reuse those metal sleeve/bushings that GM installed on the outer two sets of bolt holes on each manifold. GM did that to allow more room for the manifolds to slide as they heat up and cool down. Use short bolts on the center pair of exhaust ports only; then use the long bolts on the outer pairs.
 

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I am thinking that grade 8 is the best for the exhaust manifolds. Can anyone confirm this? Please let me know.
Quite a few people have broken grade 8's as well. They're better, yes, but not the best. Problem is the accelerated oxidation the steel undergoes as a result of heat cycling.

Best is to go stainless. 316 class stainless best pairs to the load characteristics of the exhaust man bolts, but are difficult to find. Commonly accessible, but much pricier than regular alloy steel bolts, are ARP's and the 17-4 PH bolts offered by RMS.
 

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McMaster should have 316 stainless steel bolts.
 

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Best is to go stainless. 316 class stainless best pairs to the load characteristics of the exhaust man bolts, but are difficult to find. Commonly accessible, but much pricier than regular alloy steel bolts, are ARP's and the 17-4 PH bolts offered by RMS.
Stainless steel bolts in cast iron is not recommended. With the intense heat the stainless bolts will seize in iron heads.

I had bought some SS capscrews to bolt my downpipes to the cast iron turbine housing on my turbos. I ran the car a couple of times, about 300 miles like that. I had to speak with the guys at the turbo shop for something and I mentioned I had upgraded my hardware to stainless... he then told me to remove those bolts ASAP and replace with regular black oxide bolts. He told me to NEVER do that because the bolts wil seize... sure enough, they needed ALOT of torque to remove. They felt like they really stuck in there... cwm3

When I ordered my new bolts from an industrial hardware supplier we use at the shop they confirmed what I had been told by the turbo shop guy.
 

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Stainless steel bolts in cast iron is not recommended. With the intense heat the stainless bolts will seize in iron heads.

I had bought some SS capscrews to bolt my downpipes to the cast iron turbine housing on my turbos. I ran the car a couple of times, about 300 miles like that. I had to speak with the guys at the turbo shop for something and I mentioned I had upgraded my hardware to stainless... he then told me to remove those bolts ASAP and replace with regular black oxide bolts. He told me to NEVER do that because the bolts wil seize... sure enough, they needed ALOT of torque to remove. They felt like they really stuck in there... cwm3

When I ordered my new bolts from an industrial hardware supplier we use at the shop they confirmed what I had been told by the turbo shop guy.
Hmmn. Could be elevated temps due to the turbo. I guess I should have mentioned that anti-sieze should always be used, but honestly, I've never had this issue w/ the stainless ARP's I have installed now and haven't heard anything like this from the hundreds of owners that use them as well.
 

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My stainless bolts have never given me any type of problems, although i do use a healthy dose of anti seize
 

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Discussion Starter · #11 ·
Well, I just replaced all of the grade 5 bolts & studs in the left exhaust manifold with grade 8 bolts. And, then I saw the additional posts to this thread...

I will certainly consider upgrading to stainless steel bolts, but at least the grade 8 should be better than grade 5.

I didn't cut the metal ribs, re-use the metal sleeve/bushings or use anti-seize.
However, I did use 2 or three washers on each 1.5" bolt. Anti-seize sounds like a good idea... as long as the bolts won't loosen up.

Thanks. I know I already over-analyze everything... But, I really do appreciate the detailed information.

For my SLP coated stainless steel headers in my '94 Roadmaster (done about 6 years ago), I just ordered the header installation kit from SLP. I am thinking there was nothing wrong with using what they sold me for that install??
 

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on the subject of bolts what size manifold bolts go in the 94 l99 i have 2 broken drivers rear and am going to attemp this today
 

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I'd say either get some OEM bolts, or go something of equiv hardness.

If you go harder, you risk damage to the heads if you encounter road debris. This might not be too much an issue on an LT... but on an aircooled motorcycle with an aluminum head it can be a problem easier.

If you run over something that gets caught up in the exhaust runners, you want your bolts to break before it causes damage to the head. It's easy to easy-out a bolt and replace it. Not nearly as easy to re-tap a head to use the next-size-up bolt once you've ripped one out.
 

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well i got the size i need 3/8 16 - 13/4 a few need shorter ones but spacers will work there gone anyways got the whole thing off and found last to bolt did break off in head, oh yeah. lol. so had to pick up a new gasket and bolt it back together but at least its quieter than it was.
 

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Well, I just replaced all of the grade 5 bolts & studs in the left exhaust manifold with grade 8 bolts. And, then I saw the additional posts to this thread...

I will certainly consider upgrading to stainless steel bolts, but at least the grade 8 should be better than grade 5.

I didn't cut the metal ribs, re-use the metal sleeve/bushings or use anti-seize.
However, I did use 2 or three washers on each 1.5" bolt. Anti-seize sounds like a good idea... as long as the bolts won't loosen up.

Thanks. I know I already over-analyze everything... But, I really do appreciate the detailed information.

For my SLP coated stainless steel headers in my '94 Roadmaster (done about 6 years ago), I just ordered the header installation kit from SLP. I am thinking there was nothing wrong with using what they sold me for that install??
dont use stainless steel a few people at 3 different stores told me not to something with the metal in bolts vs the head will seize, or was that chrome bolts, fk im am confused mow. but all i used were ones i picked up at home crapo for .89 cents each and some fender washers 98 cents for 10 but they are grade 8 bolts
 

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Has anyone posted a list of the exact length needed for each side of the vehicle?

I would like to get all eight bolts, but I'm not sure how many of which to get.

And one post said there are a couple of bolts that are dealer only, is that the only option on those?

Thanks
 

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Has anyone posted a list of the exact length needed for each side of the vehicle?

I would like to get all eight bolts, but I'm not sure how many of which to get.

And one post said there are a couple of bolts that are dealer only, is that the only option on those?

Thanks
i didnt write this but here you go



3/8 = M9.5
MOST use 3/8
Parts list shows
QTY 9 Bolt 3/8-16 x 1-5/8 P/N9441548
QTY 2 Stud (no size listed) POS 1&3 P/N 10242055
QTY 1 Stud (no size listed) P/N 14037662
QTY 8 Spacer (no size listed) P/N 10231254

Most use 3/8-16 x 3/4 with headers (assume 1/4-3/8 flange so 1/2" inside head
Take 1/2" & add to your manifold thickness & go to the hardware store for some GR8
You can also GET threaded stock properly sized or make your own studs.
If the bolts dont strech or shear (being GR8 & all) the studs should be fine.
 

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Has anyone posted a list of the exact length needed for each side of the vehicle?

I would like to get all eight bolts, but I'm not sure how many of which to get.

And one post said there are a couple of bolts that are dealer only, is that the only option on those?

Thanks
From a post I have save from years ago...

94-96 Impala SS LT1 Exhaust Manifold R&R Parts List

QTY P/N: Description Notes
6 10220453 Manifold to Pipe Studs 3ea. per side
6 11516072 Manifold to Pipe Nuts 3ea. per side

2 88891747 Manifold to Pipe Gaskets 1ea per side
60988 Felpro P/N (1/2 cost of GM)

2 12552469 Manifold to Head Gaskets 1ea per side
? 10231254 Manifold Bolt Spacers typically need 2ea +
1ea for each broken bolt
1 14037662 Manifold to Head Stud (FWD/R/H) Option
1 10055726 EGR Pipe Gasket to Intake Manifold Option

10 1.5” X 3.8”-16, Grade 8 Bolts Local Supply
10 88891769 GM Grade 8 Bolts Stock or “Resto” Guys $

as an FYI, here's a pic of the fasteners I removed from my 96 9C1

(The LR was broken flush with the head, so that's why only 11 are pictured)

 

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Felpro/Exhaust Manifold GasketPrice:$10.99


Part Number: MS95585
Alternate Part Number: AMS95585
Warranty:1 YR
 

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From a post I have save from years ago...

94-96 Impala SS LT1 Exhaust Manifold R&R Parts List

QTY P/N: Description Notes
6 10220453 Manifold to Pipe Studs 3ea. per side
6 11516072 Manifold to Pipe Nuts 3ea. per side

2 88891747 Manifold to Pipe Gaskets 1ea per side
60988 Felpro P/N (1/2 cost of GM)

2 12552469 Manifold to Head Gaskets 1ea per side
? 10231254 Manifold Bolt Spacers typically need 2ea +
1ea for each broken bolt
1 14037662 Manifold to Head Stud (FWD/R/H) Option
1 10055726 EGR Pipe Gasket to Intake Manifold Option

10 1.5” X 3.8”-16, Grade 8 Bolts Local Supply
10 88891769 GM Grade 8 Bolts Stock or “Resto” Guys $

as an FYI, here's a pic of the fasteners I removed from my 96 9C1

(The LR was broken flush with the head, so that's why only 11 are pictured)

Two studs are for alternator brackets. What is the third stud for?
 
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