Exhaust Manifold Nuts

[Roger S.]

What is the correct type nut to use on the exhaust manifold stud: brass, steel, standard or long length, w/wo lock washers? The nuts keep coming loose and falling off so I am wondering what is the "correct" way to go. The Corvette is a 1973 L-82 w/ automatic.
Roger

[John H.]

Re: Exhaust Manifold Nuts

The originals were triangular-crimped steel prevailing-torque nuts with a short collar on them (no washers); Paragon has them. I usually run a 3/8"-16 tap through them first to reduce installation torque required.

[Joe L.]

Re: Exhaust Manifold Nuts

John and Roger-----

The nuts that John described are definitely the correct nuts as used originally on the assembly line. However, the combination of their prevailing torque design and the corrosion that inevitably occurs with respect to the steel studs and steel nuts can make these things nearly impossible to remove when that time comes. If you're lucky, the stud will rotate out of the manifold before the nut comes loose. However, the studs often "weld" themselves to the exhaust manifold, too.

For SERVICEABILITY, I use stainless steel studs and the long brass nuts with stainless steel lockwashers. If you use these in conjunction with sintered iron do-nut gaskets, you'll have very little problem with the nuts falling off or loosening. You might have to slightly tighten them every couple of years, at the most.

[Jim T.]

Re: Exhaust Manifold Nuts

Joe where do you buy the sintered iron do-nut gaskets?

[Mike M.]

Re: Exhaust Manifold Nuts

i get mine at the local speed shop. believe they are supplied by mr gasket. check your local speed shoop or Summit. mike

[Mike M.]

Re: Exhaust Manifold Nuts

john: i'm told that full size chevy pickups of the 90's with 350 ci used a nut that nearly perfectly conforms to the shape of c-2 and 3 nuts BUT since they are metric threaded, you have to run a coarse tap thru them before installing on old vetts. friend gave me a couple he got out of junk yards and i ran a tape and they are holding well after 3 years or so. mike

[Joe L.]

Re: Exhaust Manifold Nuts

Jim and Mike-----

My source is GM. Here's the scoop:

2" size= GM #3731062

2-1/2" size= GM #3768711

The above covers it all from 53 to 82. In my opinion, these are the only way to go; far superior to the "asbestos"-type donuts. You often get a set of the 2" variety for "free" with GM oil pan gasket sets for 75+ Corvettes (also used with the GM #360866 and 359942 63-74 SERVICE oil pans).

[Dennis C.]

Re: Exhaust Manifold Nuts

Joe - The first time I've had a different opinion. SS studs and brass nuts w/lock washers may work if you tighten them every 100 miles. I've met guys with brass nuts, but they have no place on an engine. I'd suggest the factory crimp nuts - and if you want, SS studs. Dennis P.S. Good meeting you @ Nashville

[Bob Simard]

SS Studs and Brass Nuts

Stainless studs and brass nuts work fine on my 60 driver, especially after I learned to use double brass nuts. It really gets loud when your doing 75 on I-80 and the exhaust pipe is 2 inches below the exhaust manifold and the top is up due to driving rain.

[John H.]

Re: Exhaust Manifold Nuts

Mike -

The Paragon nuts are the best I've seen in terms of physical configuration - exactly like the originals. However, they're zinc-plated, and the originals had a darker uneven black oxide-like coloration; handled thousands of them when I was hanging exhaust systems on Chevy II's and Corvairs at Willow Run in 1964