Manifold Heat Valve
 

54' - 235
Was frozen up, free now, spring in good shape.
How it works ? ? ?
When engine is cold, the spring holds the shaft in the CW direction when looking from the front of the engine. The counterweight is on top and a little to the right.
Bring the engine up to temp., and nothing changes.
The spring is preloaded about half a turn.
I understand this is to preheat the intake, then open up (actually close) to divert the exhaust away from the intake when the bi-metal spring gets hot.
Am I on the right track ?
Thanks for any help here.

Re: Manifold Heat Valve
 

Yep, in the cold position it diverts the exhaust to heat the intake and when it heats up the valve opens up to the exhaust go down the pipe in a more direct path.

Re: Manifold Heat Valve
 

Thanks for the verification !

Now, the crux of the post is:
When the engine gets warmed up, nothing happens at the valve.
Maybe the spring is wound too tight ?
Is hot at idle enough to swing the valve ? or, is it only hot enough under load to swing it ?
I would think it should close and stay closed as long as the engine is at op temp. Like the spring for the choke.

Thanks again,
;)

Re: Manifold Heat Valve
 

As the spring heats up the metal gets longer. Combined with the weight this allows the valve to open. If the manifold is hot to the touch the valve should be open although it might not be fully opened. There wasn't a bunch of spring pressure unless the engine was pretty cold. If you tried to "wind" a loose spring you would usually damage the spring and it would never work correctly again.

Re: Manifold Heat Valve
 

Flip the spring over. Perhaps it's on backwards?

Re: Manifold Heat Valve
 

On my 49 216, once the engine heats up and the spring relaxes it doesn't fully close the heat valve, instead it uses the increase in rpm and exhaust gases to fully close it. I can watch it move when doing this. When the engine is cold and the spring tension is taught the flapper doesn't move no matter how high I run the rpm.

The service manual shows it pretty good. Be sure to go to the next page as it shows how the spring should be installed. http://chevy.oldcarmanualproject.com...47ctsm0604.htm

Dave

Re: Manifold Heat Valve
 

cut it out. they rarely work right after a few decades