I could use a 1974 slant six manifold heat control valve expert!

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cruiser

cruiser

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Hi Guys/Gals: I think the manifold heat control valve on my 1974 slant six Duster is messed up and I could use your advice. Recently, I removed my exhaust manifold and had it ceramic coated. It looked great when it came back, and I noticed that the heat control valve counterweight and spring had also been ceramic coated. Anyhow, I noticed immediately upon first driving the car with the refinished exhaust manifold that the engine sounded very "boomy". It was noticeably louder than before, so I checked the exhaust manifold gasket and also the gasket between the intake and exhaust manifolds. All looked good. I then noticed that when the engine was hot, the end of the counterweight spring was not resting against the peg on the exhaust manifold but was dangling at about the twelve o'clock position (straight up - see photo which was taken when the engine was hot). After 15 minutes of cooling, the spring end was now arched over counterclockwise and resting against the peg. I don't think this is right. My FSM says that when you rev the engine, that the counterweight should turn 1/2" counterclockwise, then go back to its original position. The FSM doesn't state whether the engine should be hot or cold when you perform this test. I've attached a photo of the spring standing straight up at the 12 o'clock position after shutting down the hot engine. The end of the spring looks like its resting against the peg, but it isn't. It's actually about 1/2" away from the peg. Shouldn't the end of this spring somehow be attached to or resting against the peg? I suspect that the guy who sandblasted my manifold might have messed this assembly up. The booming sound coming from the engine concerns me, and I don't want to damage my motor. Does anyone understand how these springs operate and how they should be connected to the stationary peg? Any thoughts would be welcome. Slant Six Dan, please feel free to weigh in if you're reading this. Thanks all!

IMG_3339.jpg
 
Not a good idea to coat the spring, it is thermostatic so is temperature sensitive. It will "windup" or "unwind" according to the temperature. If I understand your description it seems to be working but is coiled one turn too loose or is installed backward. Cold at rest the butterfly should be closed and the spring against the stop and tensioned. When heated the spring should relax and allow the butterfly to freely open.
 
I can tell you how mine worked before I changed to the 225 and blocked it off. When the engine was cold, the valve would open on hard fast acceleration. When hot, the valve was barely closed at idle, but opened easily when the throttle was cracked. Whether that's "correct" or not, I don't know. On my present manifold, I have the valve removed and the hot air to the intake completely blocked off.
 
"Boomy" sounds like you've got a big exhaust leak. Which gaskets (brand) did you use when assembling and installing the manifolds?

Ceramic coating on the spring is not good. That's a bimetallic strip wound into a spiral. It wants to be naked metal in order to function properly.

With the engine cold, grasp the counterweight and rotate it anticlockwise (as viewed from the front). It should turn easily, but there should be noticeable spring tension. When you let go, it should promptly spring back clockwise until it hits a hard stop. The total amount of rotation from one extreme to the other is roughly 90°.

With the engine hot, do not grasp the counterweight without a heatproof glove or something, or you'll burn yourself. But everything should work the same as described for a cold engine, except the spring tension should be less.

That valve is there for a good reason and unless you're building a race car, removing/defeating it is all drawback, no benefit.
 
slantsixdan said:
That valve is there for a good reason and unless you're building a race car, removing/defeating it is all drawback, no benefit.
Click to expand...
I've never seen you say that when you recommend Dutra Duals. :p:p
 
They probably stretched the coiled spring when they sand blasted it, so that spring is probably junk.

We cut those heat riser butterflies out of the manifolds on the engines we do. Once the shaft of the butterfly is removed a person can weld the steel insert sleeves shut with a wirefeed so they don't leak exhaust.

Never liked the thought of those stuck butterflies running half closed blocking the exhaust flow.
 
slantsixdan said:
"Boomy" sounds like you've got a big exhaust leak. Which gaskets (brand) did you use when assembling and installing the manifolds?

Ceramic coating on the spring is not good. That's a bimetallic strip wound into a spiral. It wants to be naked metal in order to function properly.

With the engine cold, grasp the counterweight and rotate it anticlockwise (as viewed from the front). It should turn easily, but there should be noticeable spring tension. When you let go, it should promptly spring back clockwise until it hits a hard stop. The total amount of rotation from one extreme to the other is roughly 90°.

With the engine hot, do not grasp the counterweight without a heatproof glove or something, or you'll burn yourself. But everything should work the same as described for a cold engine, except the spring tension should be less.

That valve is there for a good reason and unless you're building a race car, removing/defeating it is all drawback, no benefit.
Click to expand...
Dan, thanks for your reply. We used Fel-Pro gaskets. I cannot detect any exhaust leaks in any of the three exhaust manifold gaskets. I'm puzzled by the end of the spring dangling free when the engine is hot. You can see that in the first photo. To me, the spring end should still be in contact with the peg, but it isn't when the engine is hot. Then I just noticed something from the FSM. I'm attaching a photo of this valve from my shop manual. Notice how the bent end of the spring rests against the left side of the peg in the FSM photo. On my car, the bent end of the spring is to the right of the peg. Does something look wrong to you when comparing the photo of my spring to the photo from the FSM? To me, it almost looks like the thermostatic spring is on the shaft backwards. The funny thing is that it was running fine (no "boomy" sound) before we removed and ceramic coated it. If it is backwards, how hard is it to turn the spring around? The part number on my manifold is 3671862, and is dated J-17 73. The factory parts manual says the exhaust manifold should be part number 3744827. I'm puzzled by this whole thing. Your thoughts?

IMG_3340.jpg
 
Does the ceramic coating get backed on? Or some sort of heat proses greater than the heat it sees while operating on the engine? Perhaps the spring wound it’s self and the ceramic coating when cured held it in that position. The butterfly is now in the wrong position do to the counter weight and no spring pressure. Posibly acting as an engine brake giving you the noise. Meybe a new one would do the trick, I don’t know, just throwing it out there
 
I believe there is a roll pin holding the weight on the shaft that would be hard enough to take out under normal circumstances do to rust and age. With the ceramic paring might make it impossible, idk. I believe that has to come off in order to slide a new spring on the shaft
 
sounds like your spring is just slippeing off its perch, can you fold that tab over the stop? Cold motor causes the spring to close the flapper, apply heat to the spring with a heat gun/hairdrier. youll see it start to move. That is the direction the force on the spring needs to be contained to move the flapper. As the heat moves the spring, the flapper should move counterclockwise, diverting the exhaust down instead up up to the intake stove. Here is a great vid on what its supposed to look and sound like. Although he is missing the factory bumpstop thingy that makes the valve not tick when it hits its stop. I dont know what material could survive that hot manifold (asbestos pellet?) but it was in a FSM I saw.
 
Casting numbers (found on parts) are not necessarily the same as part numbers (found in cattledogs). Yikes, I do not think I would have put the money and effort into ceramic-coating an old manifold; if I were bound and determined to have ceramic coating for whatever reason (…?), I would have started with a new manifold. Too many failure modes for old manifolds—warp, crack, heat valve failure.

Fel-Pro (or other parts store) Slant-6 manifold gaskets aren't quite a guaranteed recipe for exhaust leaks, but almost—especially at the intake-to-exhaust "hotbox" junction. It is always very much worth your while to get the good gaskets for the manifolds-to-head and intake-to-exhaust junctions; R&Ring the manifold stack is a bіtch of a job, especially if your spine isn't 18 years old any more, and do-overs are even less fun. You are facing a do-over; there is nothing other than an exhaust leak that will cause a new "boomy" noise under the hood after manifold replacement.

To figure out that spring-unwinding thing you're seeing, check if the heat valve can be rotated against spring tension as previously described.
 
cruiser said:
Notice how the bent end of the spring rests against the left side of the peg in the FSM photo. On my car, the bent end of the spring is to the right of the peg.

View attachment 1715995366
Click to expand...



In the 1970 FSM, the bent end of the spring is on the right side of the pin. Like on your car, Cruiser.
But it's a 1970 configuration, not 1973 (and the viewing direction isn't specified).
heat control valve (1970).jpg

ASAP, I will check on my '71 198ci the mounting direction of the spring

François
 
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Cruiser, I checked my heat control valve today and the spring is in the same direction than yours.
The bended end of the spring rests on the right side of the pin.
A little bit hard to see on this bad picture, but the assembly is identical to yours.
HCV.jpg


Spring.jpg



Two clumsy homemade schemes to explain the heat control valve operating :

- Cold engine
HCV schema (cold engine).jpg


- Hot engine
HCV schema (hot engine).jpg


Hoping to have been helpful
François
 
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French demon said:
Cruiser, I checked my heat control valve today and the spring is in the same direction than yours.
The bended end of the spring rests on the right side of the pin.
A little bit hard to see on this bad picture, but the assembly is identical to yours.
View attachment 1715995940

View attachment 1715995941


Two clumsy homemade schemes to explain the heat control valve operating :

- Cold engine
View attachment 1715995960

- Hot engine
View attachment 1715995961

Hoping to have been helpful
François
Click to expand...
Just solved the booming engine problem. Apparently, when the guy was sandblasting my exhaust manifold he dislodged the position of the thermostatic spring on the counterweight shaft. When I repositioned it correctly, I tested it as per the recommendations above and it began working perfectly. A road test confirmed that the boominess from the exhaust was gone and all is well. Thanks as always to my MoBros for steering me in the right direction. My slanty is happy again!
 
French demon said:
Cruiser, I checked my heat control valve today and the spring is in the same direction than yours.
The bended end of the spring rests on the right side of the pin.
A little bit hard to see on this bad picture, but the assembly is identical to yours.
View attachment 1715995940

View attachment 1715995941


Two clumsy homemade schemes to explain the heat control valve operating :

- Cold engine
View attachment 1715995960

- Hot engine
View attachment 1715995961

Hoping to have been helpful
François
Click to expand...
Merci, Francois. Your comments were indeed helpful!
 
French demon said:
Cruiser, I checked my heat control valve today and the spring is in the same direction than yours.
The bended end of the spring rests on the right side of the pin.
A little bit hard to see on this bad picture, but the assembly is identical to yours.
View attachment 1715995940

View attachment 1715995941


Two clumsy homemade schemes to explain the heat control valve operating :

- Cold engine
View attachment 1715995960

- Hot engine
View attachment 1715995961

Hoping to have been helpful
François
Click to expand...
Nothing clumsy there at all! Great diagram and explanation!
 
cruiser said:
Just solved the booming engine problem. Apparently, when the guy was sandblasting my exhaust manifold he dislodged the position of the thermostatic spring on the counterweight shaft. When I repositioned it correctly, I tested it as per the recommendations above and it began working perfectly. A road test confirmed that the boominess from the exhaust was gone and all is well.
Click to expand...

I'm glad to have been wrong; let's hear it for not having to do another manifold R&R! Though I remain baffled at what was causing your noise; maybe what you meant by "boomy" is not what came to my mind with that word.
 
slantsixdan said:
I'm glad to have been wrong; let's hear it for not having to do another manifold R&R! Though I remain baffled at what was causing your noise; maybe what you meant by "boomy" is not what came to my mind with that word.
Click to expand...
Thanks, Dan. And thanks for the recommendation about the correct manifold heat control valve solvent. I went out and bought a can of the Mopar Rust Penetrant that you recommended and lubed the shaft up with it. Everything works perfectly and smoothly right now - just like a brand new valve. That stuff is amazing!
 
cruiser said:
Thanks, Dan. And thanks for the recommendation about the correct manifold heat control valve solvent. I went out and bought a can of the Mopar Rust Penetrant that you recommended and lubed the shaft up with it. Everything works perfectly and smoothly right now - just like a brand new valve. That stuff is amazing!
Click to expand...
I wasn't aware the stuff was still made. Can you post a pic and a part number?
 
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