SS exhaust manifold studs/nuts question

[aleccolin]

I can order a set of stainless exhaust manifold studs and nuts, but have a choice of SS or copper with regards to the nuts. Copper costs a couple bucks more. Is there any advantage, disadvantage? What's the primary reason for using copper, sieze resistance or strip resistance (stud out of head due to overtorque)?

Additionally, the set that comes with SS nuts includes SS lockwashers also in addition to the SS flatwashers, but the set that comes with copper nuts lists them as "locknuts" and does not include lockwashers at all. I'll be using a slowboy cast manifold that has an extra-thick flange, and the studs don't say anything about being any longer than stock, so I'm thinking the use of that lockwasher in there with the SS nut set might be bad, taking up a valuable extra thread or two on the stud.

Opinions?

 

[Defiant]

Steel studs (not stainless) and Monel nuts.

 

[aleccolin]

why not stainless studs? And what are Monel nuts, is that a brand or type?

I may be able to get some longer studs made, which would be great, since I would then not have to worry about coming up short.

 

[aleccolin]

Okay, evidently monel is the material that the "copper" nuts are made from. It's actually a copper-nickel alloy with the following composition:

66.5% Nickel & Cobalt
1.2% Iron,
31.5% Copper
Carbon 0.3%
Silicone 0.5%

What specifically about the design that makes them a "locknut" I'm still not sure.

Monel is highly corrosion resistant and resists galling, therefore resisting seizure to the stud. It is, in most cases, considered superior than stainless steel.

That still leaves the question, what reason is there to NOT use stainless steel studs (made to length) with the monel nuts. I would consider their strength and corrosion resistance properties desirable and the chance of siezure due to galling is even less with the SS stud/monel nut combo than with all stainless.

 

[Defiant]

What specifically about the design that makes them a "locknut" I'm still not sure.

They may have deformed threads, be crushed out-of-round, or be cut and pinched to create a locking thread.

That still leaves the question, what reason is there to NOT use stainless steel studs (made to length) with the monel nuts.

I don't like the stainless in aluminum. I don't know if I've ever heard why, or if there really is a problem between aluminum and stainless.

And you are aware that studs have two different-sized threads between one end and the other? The end with the flatter or concave finish will have a tighter interference than the rounded-off, more finished end.

 

[phatTSi]

I have the stainless studs from FFWD connection and I like them a lot. I've never heard of a problem between stainless and aluminum.