Stainless steel exhaust manifold bolts

[Mikey von]

While reading MaxPF's CTD build tread, I noticed he uses stainless steel bolts on his exhaust manifolds. I would like to use new hardware on my exhaust manifolds and I am thinking of using stainless steel.

Anyone see any issues with this? Is there a special type of stainless that needs to be used?


Here is MaxPF's response to someone questioning the use of stainless steel bolts;

Also, I would very strongly suggest you pull out those stainless bolts and replace them with regular g8 steel. I have been down this road too and I can tell you it can be a nightmare. Stainless will gald after many heat cycles and you an have a mess on your hands. The antiseize will help, but still not a good idea on exhaust stuff. They snap so easily.

Interesting, since my experience has been the exact opposite. I have found that once alloy steel bolts (i.e. Grade 5,8 or metric 8.8,10.9) have gotten hot enough in an exhaust system they will often seize in their holes, and they end up having about as much strength as a Grade 2 bolt (if that) so they will twist off with very little effort. Anti-seize helps with later removal, but they still rust badly and have a tendency to lose their threads because they get so soft. Stainless pretty much maintains it's strength, and I haven't seen it have any tendency to gall. Then again, I always use anti-seize on exhaust bolts.

A good example are the headpipe bolts screwed into the manifolds of the 6.2 I just removed. When I installed that engine I used stainless steel bolts with anti-seize to hold the flanges onto the manifolds (one rusted alloy steel stud on one manifold and two on the other had broken during removal of the pipes in the original install). When I went to remove them yesterday they broke loose with the same approximate force as I had tightened them with and cleanly unscrewed from the manifolds. They were discolored from the heat, but none the worse for wear. I have never had a steel manifold flange bolt be that easy to remove even after only a month of use.

An example of the perils of alloy steel bolts is the 12mm exhaust manifold bolt my friend Brian broke off in the head of his 12V while trying to remove it with a 3/8" drive ratchet, or the 2 12mm turbo mount studs I broke off (and had to extract by TIG welding a nut to them) with a regular box end wrench. The bolts had become so soft it felt like I was twisting off aluminum. Anyone who has removed many exhaust fasteners knows exactly what I am talking about.

 

[SmithvilleD]

ARP makes some very nice exh manifold studs in their stainless 300 alloy (if memory serves). They're both strong & don't have corrosion issues. Don't know if they make them in the right size for the 6.5?

The bolts/studs that mount the exh manifolds to the heads are a unique thread shape. Don't know if the corresponding thread in the heads is unique? Would seem logical the unique thread is to keep the bolts from loosening while at the relatively low torque spec & resulting clamp load used to hold the manifold sealed to the head. Prolly low clamp load to allow some expansion/contraction movement btwn head & manifold as things heat & cool.

Another thing worth remembering w/ many exh system studs, is that the nut is often some type of locknut (often copper/brass, or some alloy of that color). So they're somewhat designed to grab onto the stud - to avoid exh leak warranty claims. Also some OEM applications used some locktight type thread sealer. So a little torch heat to release that may be in order. Some stock engines are assembled w/ locktite on the studs in the heads. Don't know if this was done on the Cummins heads? If so, again a little torch heat may be in order to release the thread sealer. Probably want to search factory service manual, etc., to confirm if they used threadsealer & if they suggest heat to release it.

For the manifold to cross-over studs, I used reg steel replacement studs, & stainless steel nuts. This avoids some of the tendency of the stainless stud/bolt combo to gall on themselves. Obviously the stud can still corrode, but it doesn't "grow" together like the stock steel stud/nut.

 

[btfarm]

Let me jump in here on stainless bolts. I design meat processing equipment so I only use stainless fasteners on them. 300 series stainless fasteners are referred to as 18-8 (for chromium & iron content) and they are equivalent to 304 or 316 stn. st'l. There's nothing wrong with them on exhaust systems but you really can't put any serious torque on them because they are much lower tensile strength than alloy steel. They will stretch more so have to be tightened more than once after break in (in this application. They aren't likely to gall because of the disimilar metals you are threading into. If you want to use stainless I would recommend studs with "matching" nuts. Meaning 300 series studs and 400 series nuts (to avoid the galling issue). Believe me, you gall up a stainless to stainless fastener and you'll wish you hadn't. I've been in that predicament at 0100 hrs in a meat plant when morning startup is at 0400. NOT FUN! If ARP has some suggested stainless hardware, that would be the way to go. I've found also that stn. st'l bolt heads have a bad habit of losing their head at inopportune times when subjected to heavy vibration and high stress. I know they rust but you can never go wrong with proper alloy steel "header" bolts. Use stainless at your own risk and check them often. In any case, a good copper permatex thread compound is important to use.
Sorry for such a long post but I thought it was important.

 

[NVW]

Let me jump in here on stainless bolts. I design meat processing equipment so I only use stainless fasteners on them. 300 series stainless fasteners are referred to as 18-8 (for chromium & iron content) and they are equivalent to 304 or 316 stn. st'l. There's nothing wrong with them on exhaust systems but you really can't put any serious torque on them because they are much lower tensile strength than alloy steel. They will stretch more so have to be tightened more than once after break in (in this application. They aren't likely to gall because of the disimilar metals you are threading into. If you want to use stainless I would recommend studs with "matching" nuts. Meaning 300 series studs and 400 series nuts (to avoid the galling issue). Believe me, you gall up a stainless to stainless fastener and you'll wish you hadn't. I've been in that predicament at 0100 hrs in a meat plant when morning startup is at 0400. NOT FUN! If ARP has some suggested stainless hardware, that would be the way to go. I've found also that stn. st'l bolt heads have a bad habit of losing their head at inopportune times when subjected to heavy vibration and high stress. I know they rust but you can never go wrong with proper alloy steel "header" bolts. Use stainless at your own risk and check them often. In any case, a good copper permatex thread compound is important to use.
Sorry for such a long post but I thought it was important.

:iagree:

Stainless also distorts (stretches) much more than steel, possible leaks?

 

[SmithvilleD]

Here's a link to ARP's catalog site.

http://www.arp-bolts.com/Catalog/Catalog.html

Click on:

Metric exhaust/acc. studs

And it will bring up the page showing the exhaust studs I've used & can vouch for the quality & strength. They're not cheap, but I've found them a close to permanent solution to exh stud issues.

They refer to their material as ARP Stainless 300, but it isn't remotely comparable to the common alloy stainless fasteners that lack adequate tensile strength.

The common stainless alloy fasteners polish up nicely in a vibratory (like ammo cartridge) polishers & stay looking nice. But they're only for non-stressed applications - sort of underhood dressup stuff.

 

[bk95td]

I use all stainless bolts on my exhaust manifolds. I believe fastenal called them A-8. They are supposed to have more tensiI strength than the 10.8 bolts they replaced. I used A-8 threaded rod for the bolts where the glow plug heat sheilds go. I wouldn't pay over $5 a bolt for the crap that was on it originally. I paid less than that for the stainless.

 

[btfarm]

I use all stainless bolts on my exhaust manifolds. I believe fastenal called them A-8. They are supposed to have more tensiI strength than the 10.8 bolts they replaced. I used A-8 threaded rod for the bolts where the glow plug heat sheilds go. I wouldn't pay over $5 a bolt for the crap that was on it originally. I paid less than that for the stainless.

That's a beauty!:thumbsup:

 

[bk95td]

That's a beauty!:thumbsup:

I loaded about 60 more pics on my album last weekend. Take a look.

 

[Missy Good Wench]

For whatever it's worth.

I have coaxed more damned broken manifold and crossover pipe bolts out of 6.2/6.5 engines than I care to think about.

I have tried stainless steel and the comments that have been made about the breakage and loosing their heads, Oh yeah.

I personally would use the stock replacement rolled thread bolts just like the beast came from MA General.

Slop the hell out of them with never seaze and let er rip.

These stock factory bolts are designed with a tri lobe swage in the threads that help keep them tight. (It works well) Just use plenty of Never seaze and your good to go.

There may be a type of stainless bolt that is better than whats available at the hardware or parts houses but Im sure they come at a steep price too.

My vote is for the stock set of bolts with the stud tops where needed.


Missy

 

[chevyinlinesix]

I am using stainless A2-70 grade fasteners, they have a 102,000 psi tensile strength, and a 65,000 psi yield strength. Also, the threads of the original bolts/studs are a common metric size and pitch. I use Never Seez® nuclear grade nickel Special Anti-Seize for anything real important.

 

[matuva]

:iagree: I think that's one the key which make things easier : anti seize...

my favorite one is the hi-temp copper one from loctite