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.

 

[longbedder]

The supplied bolts that hold the downpipe to the turbo exit on a Banks setup are stainless. You can bet that those suckers get plenty warm. I've had them in and out several times with no problems at all.

In addition, there are some late-model engines that are supplied form the factory with stainless exhaust fasteners. Ford applied it as a fix on their V10 Tritons - the rearmost carbon steel exhaust bolts were famous for snapping and the fix was to go stainless.

Heat by itself does not gall stainless steel, BTW. Machining and "interference cutting" with other parts does. You can help avoid galling bolts with coatings (like anti-sieze).

I believe you want a 304 alloy, in class A3 or A4.

 

[Mikey von]

some others at diesel page and diesel place seem to think that the stainless steel and cast iron will not play nice together, galvanic corrosion. I have no clue. I need to get a hold of MaxPF and see what he says.

 

[longbedder]

Any two dissimilar metals will have some degree of galvanic corrosion - that includes carbon steel and cast iron (like traditional exhaust bolts in heads). The greater the difference in values of electrochemical potential between the materials, the more (faster) corrosion you'll get. Carbon steel and cast iron have very similar electrochemical potential (iron has the higher value). Cast iron and 304 stainless are just about as similar but in the opposite sense (same-ish difference in value, but stainless has the higher value).

I realize you're putting a lot into this, but this is one of those things that I wouldn't worry about too much.

Edit: there is a very large difference in the various stainless alloys. Make sure you get the right one if you do go this route.

 

[diesel4me]

I had a nightmare when I snapped off stainless steel studs I put on the manifold to pipe connections on my 72 K5 many years ago--about 3 years after I put them in ,using never seize,the pipes needed to be replaced,when I went to take the nuts off (also stainless) the studs snapped off like glass..no drill I had would even scratch them,so I ended up taking the manifolds off and having them milled out with an end mill at a machine shop--busted 2 bolts off in the head too,that held the manifol on,those were a joy to drill out--used the manifold as a guide,I just bolted it on and used a 3/8" bit to start the hole centered,then used a 3/16" one and went up in size till I got to 5/16",and re-tapped them..one came out with a 5/16" left handed bit,the other one I busted the tap off in the head..--had to use a cutting torch to vaporize it,luckily I got it all out and was able to tap 3/8:" threads in the hole again..

Not sure I'd use stainless studs again,ever!..but I have used stainless steel nuts on regular studs and they actually came off OK a year or two later..I liked the brass nuts that were deep thread,at least those can be melted off without hurting the studs much if they seize..

 

[DEMON44]

I had stainless hardware holding the twin turbos together on my old dodge. I had them on and off 3 or 4 times in a couple years. they galled up pretty bad a I had to break 2 to them to get the nuts off. I can offer that Detroit Diesel, MTU, or MBE don't use any stainless hardware.

 

[kennyw]

I had a nightmare when I snapped off stainless steel studs ...when I went to take the nuts off (also stainless) the studs snapped off like glass..

Stainless steel only galls with stainless steel of the same grade. If you use stainless studs, you need a different grade of stainless nuts to prevent problems. Putting stainless bolts into a cast iron head will not be a problem.

 

[MaxPF]

First off, you have to use the proper alloy stainless. That's actually pretty easy since the two most common grades used for bolts are 304 and 316. These are both austenitic grades, which means they have enough nickel to prevent the formation of martensite (which is what makes steels, stainless or otherwise, hardenable). 304 is also commonly known as 18-8 or A2, and is the most common and least expensive. 316 costs more, but has better corrosion resistance against acids and marine environments. You don't need it for exhausts, but it might be better if you live in some rust belt hellhole where they salt the roads (which is what makes it a hellhole, not the fact it's cold or snowy ). These stainless steels will not become hard or brittle through heat cycling (I have no idea what diesel4me was using, but it wasn't an austenic grade of stainless), nor will they become much softer or weaker. They aren't as strong as grade 8 though, so don't try to tighten the crap out of them - you don't need to anyway. Fortunately, they are quite a bit stronger than grade 8 bolts that have been heat cycled a bunch of times, and they don't turn into a rusty pile of crap.

You absolutely MUST use HIGH TEMP anti-seize on the threads! This goes for any exhaust bolt, not just stainless. A regular grade 8 will still turn into a rustball, but if you use good anti-seize you will probably get it back out without breaking it off. The regular silver stuff made by Permatex and others seems to be OK when threaded into heads (which are cooled by coolant), but there is better stuff out there. I use Jet-Lube KOPR-KOTE, which is good up to 1800 degrees F. That's hotter than most exhaust systems will ever see, and I've always had good luck with the stuff. They make stuff good up to 2600 degrees, but it's spendy and I think the copper stuff works better at "lower" temps.

One other thing. I got my exhaust bolts for the Cummins from McMaster-Carr. They were cheaper than any of the local bolt and nut places, they actually had what I wanted, and I had them the next day (only because I live in an adjacent state) even though I didn't place the order 'till 6PM! Gotta love their service

 

[protechk5]

Mikey Von, so what did you end up getting? I need to get some new ones and cant find any locally.

 

[Mikey von]

I could not find any local either with the special low cut threads. I actually just put the exhaust manifolds on last night and reused bolts and studs. I had almost 3 whole sets to choose from, so I choose the best looking ones and said good to go.

 

[MaxPF]

I could not find any local either with the special low cut threads. I actually just put the exhaust manifolds on last night and reused bolts and studs. I had almost 3 whole sets to choose from, so I choose the best looking ones and said good to go.

What's so special about 6.2 manifold bolts? Just go to McMaster-Carr and order what you need in stainless steel (304 or 18-8 - same thing). You will have them the next day. I can't remember what size they are...

While you're at it, get some copper anti-seize like Jet-Lube Kopr-Kote or another equivalent as well.

 

[protechk5]

I have no idea, but i did read over on diesel place that they have a special rolled thread with a triangle shape to the base of the thread to lock them in the head.

 

[MaxPF]

I have no idea, but i did read over on diesel place that they have a special rolled thread with a triangle shape to the base of the thread to lock them in the head.

Many of the bolts on the 6.x motors are like that. It's not necessary though - the Cummins has no fasteners like that, and they don't have problems with bolts backing out. KDP yes, but not bolts

The exhaust bolts are probably M10x1.5 pitch. Measure one with a dial caliper - 10mm is .394", so if it measures within a few thou of that figure, then that's what it is.

 

[Speedo]

The type of anti-seize makes a difference, I prefer the ones that use a bit of copper. The most common ones use a bit of aluminum. I still have a small can of Irontite 999 that uses lead, worked great for exhaust. Can't get that stuff anymore.

Gus