SS studs for exhaust manifolds

[Jim R.]

when using ss studs is it best to use ss nuts and lock washer or brass nuts, also if there any advantage to using the tall brass nuts vs the short for staying tight. thanks JR

[Gene M.]

Re: SS studs for exhaust manifolds

Jim,
Stainless on stainless is good for rust avoidance. But if one gets over zellis in tightening the nuts the stainless will gall. So use anti-seize for good measure. As far as brass, it is good with 300 stainless for electrolytic action between metals. The brass gets crappy looking over time. I prefer stainless on stainless and have had good results using anti-seize.

[Joe L.]

Re: SS studs for exhaust manifolds

when using ss studs is it best to use ss nuts and lock washer or brass nuts, also if there any advantage to using the tall brass nuts vs the short for staying tight. thanks JR

Jim------


Stainless steel studs for the exhaust manifold-to-pipe connection are the ONLY type of studs I will use. Period.

You can use either the brass nuts (I prefer the long ones) or stainless steel nuts. If stainless are used you definitely need to use anti-seize compound as Gene mentions. However, you need to use high temperature, nickel-based anti-seize. This is more expensive than regular anti-seize, but it's the best way to go. You can use it for all anti-seize applications and one container will last you a lifetime.

[Larry M.]

Re: SS studs for exhaust manifolds

Jim:

I think that just the standard carbon steel interference nuts should also work okay. Carbon steel cannot rust to stainless, and it also cannot gall. Thermal expansion is similar. It (CS) is better than brass.

As pointed out by Joe, I would suggest a (very) high temperature anti seize for this application. My recommendation above is what I would use on my own car.

FWIW.

Larry

[Michael G.]

Re: SS studs for exhaust manifolds

Regarding all these combinations:

1) Stainless studs with stainless nuts won't corrode, but a stainless lock-nut is too soft to work well as a locking device, so its just about worthless. Additionally, with stainless on stainless, friction is very high, so, galling will be an issue. Don't use without anti-seize.

2) Stainless studs are much softer than hardened carbon steel lock-nuts and the high friction of a steel lock-nut will cause galling of the thread surfaces of the softer stainless material, (even with anti-seize). Not a good combination.

3) Stainless studs, with thick brass non-locking nuts, and anti-seize is the best of all the combinations. It won't corrode badly and won't seize due to galling, but, you'll need to re-tighen occasionally.

The prevailing-torque, hardened steel lock-nuts GM used in this application were waxed after plating to achieve a specific friction in the threads during initial installation. This avoided galling, but the wax is gone in this usage after the initial installation. In any case, I doubt the ones you get from repopers are waxed, let alone to a specific friction, so use anti-seize, if you use lock-nuts.

No matter what you use, the thermal cycling will cause you to eventually lose clamp-load in the joint. The differences in thermal expansion of these materials makes little or no difference. The prevailing-torque (lock) nuts are there only because they won't vibrate off when they get loose due to the lack of clamping. There really is no good solution available for a reasonable cost, except to re-tighten the nuts periodically, so, you want to use a combination that won't seize from rust. If you do this, you don't need to use the lock nuts.

[Stuart F.]

Re: SS studs for exhaust manifolds

I have the SS studs alright, and the longer brass nuts. They have been on as long as my aluminized exhaust system, which would be since 1996. I have never had to re-tighten them, but had sprayed them a couple of times (RH side) in preparation for removal/replacement of the heat riser valve with a spacer. They came off easy and went back on easy as well. I must admit, I believe my car has only been out once in a brief rain since 1996 and I avoid puddles. The underside looks almost as clean as when I did a rehab in 1976. It's not a trailer queen, but's been babied and has been to shows and cruisins, as well as Sunday morning rides for quite some time - away from the elements.

Stu Fox

[Gene M.]

Re: SS studs for exhaust manifolds

Guys, I drive my 65 all the time even hard down poring rain. Been a road tours and vacation with it a lot. The stainless on stainless studs and nuts have not loosened nor should they any more than regular steel. I use a flat washer and lock washer in each application and this is going on 30 years.

PS everything else is getting rust but the hardware securing the stainless pipes to the manifold is not........

[Jim R.]

Re: SS studs for exhaust manifolds

Thanks folks for all of the good advise.
Jim