Exhaust pipe nuts

[flatford39]

So I found all the pieces to put my 1980 K10's exhaust back to factory OEM. I removed the old dual exhaust system and am in the process of re-installing the new OEM parts.

When I removed the nuts holding the exhaust pipe from the cast iron exhaust manifolds I was surprised to find that they were brass nuts that are about three times the length of a regular nut.

Are these self chasers or something to clean up the threads on the studs???

I just don't remember these being brass in the past. Are these OEM or something else.

Thanks for any response.

 

[bucket]

I don't know if that's what GM used to begin with, but those are indeed the correct nuts. I think the material and length keep them from backing off.

 

[chengny]

It has to do with the ball & socket design of that joint. The idea is to allow relative motion between the manifold and the exhaust piping as the engine rotates on it's longitudinal axis when a load is applied.

In order to keep a seal - and still allow the donut to float within the swaged end of the exhaust pipe - it requires a spring loaded clamping force.

So, instead of just making a permanent joint using steel nuts, the joint was held together with springs backed up by brass nuts. This allowed for continual adjustments if necessary.

The reason they specified brass for the nuts was that they would not seize to the steel studs. And, as Mr. Bucket suggests, they are designed to be longer due to the relative softness of the brass. The longer the nut, the more thread engagement and the more thread engagement the less the chance of stripping the threads.

This only applies to the ball/socket type joint (i.e. with a donut type gasket and exhaust pipes with swaged ends). If you have a flat face-to-face type joint, the springs and brass nuts are unnecessary - you can use steel fasteners and make the joint up tight.


This is my theory and I'm sticking with it.