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Exhaust heat riser - is it open or closed?

David Womby

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I've looked at other threads but don't see an answer to my question. So here goes.

My car has the 360 from a 78 Monaco complete with stock exhaust manifolds including the heat riser on the right manifold. The car is on stands right now for other work and not running. The heat riser is well and truly stuck. It's one like these parts from Mancini fit. Is there any way to find out if it stuck in the open or closed position - maybe by the orientation of the markings embossed in the circular part? I really don't want to drop the exhaust if I don't have to but expect that's the only way to know.

Thanks
David

mancini-racing-heat-riser-18.png
 
The counter weight is machined for the stop spring . If the stop pin is still in the manifold you should be able to figure it out. Looking at google images might help. Or just drop the pipe and see where the flap is.
 
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If the spring is still attached you can see which way the shaft should rotate higher temp the spring will want to unwind.
 
Thanks, gentlemen. The engine compartment of my Bristol 408 is very narrow but the factory shoehorned the V8 into it. Unfortunately that means the riser is only visible from below and barely but I'll try to checkout the pin and spring.

David
 
I had another look today. I also found this thread over on C bodies which seems helpful. Another heat riser question (1970). Is 720 degrees normal?. One of the people posting there, HWYCRZR, describes his 1970 heat riser, as turning clockwise to open and that the Chrysler symbol is at the bottom of the counterweight when fully open.

On mine, the spring and pin are both still there (see pic) and it looks to me as though the spring would turn the weight clockwise as it heats up.
20240203_144203.jpg
but I think it may be seized in the open position because the spring is quite loosely wound as thought it was extended and the Chrysler symbol is almost at the bottom of the weight (it's at about the 5 o'clock position).
20240203_144307.jpg

Of course, I am assuming my weight and spring are the same as the 1970 one HWYCRZR describes but I think I will leave things alone in the hope that I am right thinking it is seized open. I will check left and right exhaust temperatures and output volumes once the car is on the road again.

David
 
I do not see the stop spring. You are right on which way it turns. We used to free a lot of them up. Mopar used to make a heat riser penetrant and lube. Lube and let sit. Tap on each end of the shaft along with trying to turn it by the weight. Keep doing that and it might free up.
 
I do not see the stop spring. You are right on which way it turns. We used to free a lot of them up. Mopar used to make a heat riser penetrant and lube. Lube and let sit. Tap on each end of the shaft along with trying to turn it by the weight. Keep doing that and it might free up.
Pardon my ignorance. What is the 'stop spring'? There is a spring between the weight and the manifold body.

David
 
Thanks. No. You're right. Didn't see anything like that. Where should it be?

David
It goes in the counter weight slot first and the the wound return spring slides in the slot. Try to google the install directions for that rebuild kit.
 
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This is close. Not sure if its exactly like yours. The FSM for your engines year would show more.

6685786-ExhaustSystem013.jpg
 
This is close. Not sure if its exactly like yours. The FSM for your engines year would show more.

View attachment 1603223
Thanks. Very helpful.

I think I have to live in hope that mine is seized open for now and check exhaust temp and flow when the engine is next running.

Seems a very complex and hard to get at system compared to a hot air duct above the manifold with a temperature operated door at the opening into the air filter! Must have benefits that I don't realize.

David
 
I haven't checked the pipe temperatures yet but there is strong exhaust flow from both pipes. So if it is seized, mine must be seized open. That's a relief!

David
 
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