C1 Exhaust Hangers and Clamps S/S

[Clare Carpenter]

Re: FWIW I ran into a problem w/ SS once...

Exactly what is galling and what causes it? I have SS studs (not yet installed) for my cast iron manifolds, I believe they came with nuts too, but I'm not sure if the nuts are SS or not. Paragon has the exhaust pipe stud, original style zinc plated crimp nuts, sold separately and not included in their SS stud kit. I think the regular steel stud kit includes the correct nuts. Regular steel nuts can and often do freeze up on exhaust studs but usually can be freed up with out breaking the stud. What advantage does the SS studs offer in this application?

[Terry M.]

Re: FWIW I ran into a problem w/ SS once...

Clare,
Some of the MEs will no doubt chime in here, but my understanding of galling is that it is the transfer of metal from one object to another (Stud to nut and/or vise versa) due to friction between the two objects. Some metals are more prone to this than others. Most stainless steels (there are many alloys of SS) succumb to this, as does aluminum. It can make shaping SS parts in a die very difficult. The lubrication requirements are extreme in order to achieve reasonable die life and production rates. This is only one of the reasons SS die formed parts are so expensive.

[Joe L.]

Re: FWIW I ran into a problem w/ SS once...

Clare-----

Galling is a term to describe pretty much what Terry described. Generally, it's caused by an interaction between metals that results in the abrasion of one or the other, or both, and initiated by mechanical friction. Sometimes, other factors can produce a condition that may be referred to as "galling", but which is not true galling. Paramount among those is dissimilar metal, galvanic corrosion.

In any event, I recommend the use of stainless steel studs and brass nuts, particularly the "long" variety, in conjunction with stainless steel lock washers. The stainless steel studs will never suffer weakening due to corrosion and the brass nuts will always be rather easily removed. It's not "correct", of course, but, in my opinion, it's a functional improvement.

Standard steel studs become hardened (and brittle) as a result of the heating and cooling cycles that they experience. While you may never have experienced an exhaust stud breaking as a result of trying to remove a rusted-on nut, it does happen. If it breaks right at the manifold (which is common), they can be VERY difficult to remove. Due to the hardening descibed, the stud remnant is VERY DIFFICULT to drill out. Stainless steel does not heat-harden as much as regular carbon steel so it's less of a problem as far as breaking is concerened. Also, since it doesn't corrode, that isn't a problem, either. It does gall, though, so the choice of mating metal (i.e. the nut) is important.

Some folks think that a self-locking nut (as originally used by GM) is necessary to keep this joint from loosening. However, while these joints do, APPARENTLY, loosen, I don't think that it's caused by the nuts loosening. Most of it is caused by the gradual, heat-induced deterioration of the "donut" gasket. That's why I don't use the standard-type "donut" gaskets; I use the sintered iron-type gaskets ONLY.

In my opinion, THE way to go is stainless steel studs, stainless lock washers, long brass nuts, and a sintered iron "donut" gasket. I check the tightness of the nuts about once a year and it's very conveniently done at the same time I do an oil change.