1960s 429 exhaust heat riser

[Julien Abrahams]

Dear all,

I am working on a '66 with the 429. It still has the thermostatic valve in the pass side exhaust pipe. The valve is free to move (not stuck) and I can move it by hand by rotating the counter weight(?).
When is this valve open? In picture 1 or picture 2?
Is it a good sign that I can rotate it by hand? I would guess it would need to be held closed by spring pressure until the thermostatic spring heats up. I cannot check it with a flame of some kind because the electrical wiring is too close.
Thanks in advance.

[Chopper1942]

It is universally called a heat riser. When the engine/exhaust manifold is cold, the spring should rotate the weight up against the stop on the heat riser (top photo). As the engine and exhaust manifold heats up, the spring unwinds and the weight drops and opens the valve letting the exhaust to exit the exhaust pipe.

To check if the valve inside is in place, start the car with a cold engine and touch the intake manifold exhaust crossover passage. It should immediately start to get hot. If it does, the heat riser is working as it should. If not, the valve inside of the heat riser could be missing and you will need to replace the heat riser.

[Julien Abrahams]

@ Mr Lamb,

You are right. I completely forgot the name. So i changed the topic title accordingly. Thanks.

[James Landi]

THese often get stuck--partially open,  and they create a partial exhaust blockage, increasing extra pressure and heat in the combustion chambers.  I recall, decades ago, the mechanic who performed a "carbon and valve"  job on my 1956, emphatically stated that my exhaust valves were burnt because the "riser is stuck partly open." Of course, there  were other mechanics who claimed the burnt valves were a result of my using "white gas" (Amaco was unleaded). These heat riser designs became more sophisticated--- (I don't think they're to be found on new cars)  And then we learned that leaded gas creates highly toxic fumes that negatively affect brain function--perhaps a reasonable cause for my enduringly irrelevant and stupid commentary on this forum!  Happy day,  James