The Virtues of Stainless Steel Exhaust Fasteners

[Jeff Higgins]

After about 15 years and just over 100,000 miles of driving, I have just now had occasion to remove the heat exchangers from my motor. The oil crossover, or return line, got dented pretty good and needs replacement. I had been dreading this job ever since seeing the damage a little while ago, with images of seized nuts, broken studs, and all of the usual joy accompanying the removal of exhaust systems.

Well, much to my surprise - and immense satisfaction - every single exhaust flange nut on every single exhaust port broke free with just a little bump, then spun off freely with my fingers. The fasteners on both flanges to the muffler did the same. No corrosion, no sticking, no broken anything, no stripped anything.

I attribute this success to having replaced all of the studs in the heads with stainless steel, and using stainless steel nuts as well. The nuts and bolts connecting to the muffler are all stainless as well. As important was the use of a good copper based anti-seize compound at assembly.

I just thought I would share, and maybe help someone save some grief down the road. I couldn't be happier - what had the potential to have been a real nightmare turned out to be a piece of cake, all due to a little extra care and attention some fifteen years ago.

[GH85Carrera]

Ain't it grand when a plan comes together!

Instead of cussing the last mechanic that touched it, (yourself) you can pat yourself on the back.

[Trackrash]

Anti-seize has worked for me. All my exhaust nuts came loose, no problem, after 20 years using stock nuts with anti-seize. I do use stainless for the muffler bolts.

Did you also use anti-seize on your stainless studs?

[Jeff Higgins]

Yes, I used anti-seize on the stainless studs. Both where they screw into the heads and where the nuts screw onto them. The hex nuts are all stainless, but the barrel nuts are the standard carbon steel cad plated. To be fair, they did not rust either.

Stainless in and of itself is probably not the only reason for my success. Galvanic corrosion would probably cause them to get stuck in the aluminum heads just as well as carbon steel studs would have. Granted, no reason to remove them from the heads, but I tried a few anyway just to see. The old double nut trick saw every one I tried spin right out like the day I put them in.

So, maybe it's more the copper anti-seize than the stainless. I'll continue to hedge my bets and use both in these kinds of environments. Not a lot of tensile load on the fastener, but a very hot, often wet environment that heat cycles every time we run the thing.

[dw1]

I too am a fan of stainless steel fasteners for this application. This has proven especially worthwhile because I switch back & forth between a stock muffler and a Dansk dual-out w. 84mm pipes.

I must admit that I did have to learn the hard way to be sure to use the high-temperature anti-seize and to be sure the bolts are properly torqued - which is especially important when using anti-seize.

[porsche930dude]

Nice. It used to be common on old cars to use brass nuts on the exhaust they dont rust up and are self locking.

[Jeff Higgins]

Originally Posted by porsche930dude

Nice. It used to be common on old cars to use brass nuts on the exhaust they dont rust up and are self locking.

Yes, the original hex nuts for my car were actually copper. They were flange nuts, with the "built-in washer" profile and the oval hole. They expand to circular when tightened, which serves as the "locking" feature. Interestingly, they were a 12mm hex rather than the current 13mm hex. I have two of the dedicated exhaust nut box end wrenches, one in the old 12mm and one in the new 13mm, just in case I'm foolish enough to think I ever need to take another old one apart.

The problem with those was, however, that the studs rusted inside of and below them. Then the copper was too soft to afford a good enough grip on the hex to get it off past the rusted part of the stud, so they would just round off. Try cutting one of those off with the heat exchangers still in place. You'll make up all kinds of new words trying.

[winders]

https://www.pfonline.com/articles/fixing-corrosion-between-anodized-aluminum-and-steel

[Tremelune]

What about copper nuts? I always see them recommended for exhausts.

Anti-seize or threadlock on every bolt unless otherwise specified...

[yelcab1]

Exhaust nuts is about the only place i would accept stainless steel fasteners.

[RSTarga]

Copper works really well too.

[911obgyn]

I think the anti seize is the key, nickel anti seize is a higher temp one if i remember correctly. I have got some copper plated nuts but dont trust them

[spuggy]

Many of the fasteners on my old Ducatii (that's the plural, right? ) gave every appearance of being assembled totally dry by the factory, plus the yellow plating would corrode if they got wet. Sigh.

So I pretty much replace the factory fasteners with stainless as I disturb them, use thread chasers (not dies or taps!) as/if necessary to remove dirt, crud galling etc and always have some of this to hand to aid future disassembly/prevent metal-to-metal contact (and thus galling from dissimilar metals):



Been using for some years now and very happy with it.

I haven't used any on the 911 exhaust studs, turbo etc yet - but it worked as expected on the wastegate studs. Really not seeing any reason not to use it everywhere.