Stainless exhaust studs and nuts

I removed some really rusty exhaust nuts this weekend (think 12mm becoming 10mm or less) I've heard that stainless is not to be used for exhaust manifold hardware due to high strength issues.

I am thinking of replacing the single nut with two stainless 18-8 nuts and double locking them? I figure i could get my strength back by adding more material. I this a bad idea?

I dunno who said not to use stainless for exhaust manifold hardware. It works fine on my turbocharged Esprit. Came from the factory that way. Use the high temp all stainless lock nuts (not nyloc). Esprits also have a lock plate that you bend over the nuts. It helps a little.

I haven't had any of the usual issues of the last nut and/or stud vanishing since going to my BSH Dr.Hess 304 stainless manifold, though.

Use generous amounts of anti-seize with stainless hardware.

it depends on where and how you use it.

don't put stainless studs in your aluminum head that holds on your cast iron manifold with copper nuts.

belteshazzar wrote: it depends on where and how you use it. don't put stainless studs in your aluminum head that holds on your cast iron manifold with copper nuts.

Except for the copper nuts part, that's exactly what Lotus did with the 910 motor.

Huh. I did that once and couldn't ever keep them tight.

Yeah, well, I didn't say the Lotus ones stay tight either. Lotus used lock nuts and put lock plates on under the nuts. I did the CAD work and had my chicken plant makers waterjet out a few sets of lockplates. You locktite the stud to the head and bend a tab on the lockplate up against the nut flat. They still came loose at the last stud or two, in my opinion because of the weight on them. The exhaust manifold hold up not only itself (18 lbs), but also the turbo and half the rest of the exhaust system. Of course, the cast OEM manifolds all crack. My BSH (Brick E36 M3 House) manifold has been holding up fine and I haven't lost a stud either.

Oh, according to my web site, I have a report of "Nordlock" lock washers available at Mcmaster.com as working well for this application.

Dr. Hess wrote: Oh, according to my web site, I have a report of "Nordlock" lock washers available at Mcmaster.com as working well for this application.

Those things work awesome. I haven't had to redo valve cover gaskets anymore because of loosening or overtightening since i started using those.

I am more worried about metal creep with the stainless hardware. The car is just for daily driving so it won't get cherry red, but I also hate redoing stuff later.

Must be why Chrysler put a brace from the the block to the bottom of the turbo on their turbo cars. The cast iron manifolds were cracking. I think if Hess and others were to add a little support brace, some of those problems might go away.

Stainless has a higher expansion coefficent than a lot of other metals. It would warm up, loosen off from the expansion and likely the fastener would loosen off. I don't think there is such a thing as an ideal fastener for exhaust side of the equation other than a material with the same expansion as the material you are fastening.

-Trent

ARP makes stainless steel studs and nuts that are designed for this application. They Work.

Inconel 718 which is a variant of Stainless Steel and with a service temperature of 700 C. It's commonly used in jet engines and other "hot" environments. It's also found on many F1 engine exhaust systems.

As for compensating thermal expansion of exhaust hardware, SAAB 9000 turbo used a long stud with a spacer and copper plated lock nut. The entire assembly has controlled expansion and contraction over the entire temperature range. It works, and the exhaust hardware stays put.

This was the kind of engineering SAAB had at one time in it's history.

Thanks everyone for the replies. I think i'll look into ARP studs.