Exhaust Manifold Heat Riser Operation

I bought a set of Big Block exhaust manifolds (70-71 383/440 HP) that has a fully intact passenger side heat riser assembly. Everything is there and turns freely. My question is about how it should operate. It would seem like the plate should be closed when the engine and manifold is cold, and when the car is started and everything gets heated up, the plate should open.

Everything looks to be in the proper places, but the plate is fully open when the manifold is cold, which seems backwards to me. Does anyone have any expertise with this setup?

It will be closed all the time without the engine running. The spring heats up and lessens the tension when running. Either the stop is missing or it is assembled incorrect.

Agreed. If correctly assembled, the valve should be closed. If you open it by hand, the spring will close it.

Is there any lubricant that needs to be applied to the heat riser assembly for storage over the winter months? A friend called me this morning asking if I new of a product that is supposed to be applied to the spring/hardware for offseason storage.

This is what I would use.

Mopar Rust Penetrant

Somebody probably purposefully installed the spring backwards to avoid the clanking of the valve at idle.

After looking at it further, I think you are correct in that the stop is missing. The stop should hold the plate in the closed position when cold, and the spring when heated, will open the plate 90 degrees. What is happening now is that the spring allows the plate to move 180 degrees, back to the open position.

Thanks for your input. Now I just have to figure out what it is that should be stopping it in the closed position.

There was a stop pin that had to be there before assembley of the riser. I think if you research pictures you will see the pin that's needed. Does the manifold have the stamped steel counter weight or the round cast counter weight? There is a difference on how they look?

Mine has the heavy round counter weight. I looked everywhere for a stop pin where one should be, but found no sign of one. I was thinking of drilling a hole on the counter weight and putting in a roll pin that would stop the assembly from going past the closed position. I simulated this buy sticking a small open end wrench inside the exhaust hole that held the plate in the closed position and heated up the weight and bi metal spring and it worked perfectly. It allowed the plate to be moved to full open at around 300 degrees. And as it cooled, it was fully closed again at around 200 degrees.

I don't know how to find any pictures of where the factory pin should be. If you know of any, please post or send a link.

Thanks!

The pin is pressed into the manifold,probably broken or rusted off,look close and you'll find it.

It should look something like this.

IIRC, I drilled a hole where the pin was located and then tapped the hole. Then screwed in a small bolt and cut off the rest with a hacksaw.

Yes, exactly like that.

I think I know what is missing. A spring steel piece that goes in next to the bi-metal spring that limits the travel of the plate. I have a picture but I can't figure out how to post it.

That is what contacts the pin. You might be able to replace it without removing the weight. If not you might be able to devise a puller to pull the weight off the shaft. Most likely it may be best to buy a kit and rebuild it.