croderique
New Member
I see a lot of discussion about “open”or “closed” position but which is the “open” or flow through position? Is the counterweight horizontal or vertical in the open position? Thanks. Chuck
Manifold heat control valve on a 383
- Thread starter croderique
- Start date
The counter weight should be at the 6 o'clock position when open.
Regardless of which style of counterweight on your valve, the valve itself should be in the vertical pisition when open. BUT the main thing is to ensure that the valve is FREE to move, rather than "tight". On my '66 Newport, the valve usually stuck in the 1/2 open position. No amount of penetrating oil would free it either.
So, I had the dealer change it the last time. There is a brass (or similar) bushing which goes into the hole in the manifold, into which the valve's shaft is supposed to rotate. No problem putting the new bushing where the old one was, BUT when the shaft was inserted into it, the shaft moved reluctantly, in that the thermostatic spring could barely move the valve toward open at ambient shop temperature. The fix? To slightoy ream the inside diameter of the bushing so that the shaft fit freely into it and DID rotate freely when assembled. On the verge of a rattle, but it moved, which was what is needed. When the engine was revved a bit from hot base idle, the valve would open with the additional flow of exhaust gases.
Eventually, the valve stuck in the 1/2 open position again. As performance was NOT changed in that position, I just left it. NOR was cold or hot starting performance. A good compromise to me. Key thing was that there could be flow to the intake manifold so that the automatic choke thermostat would work as designed.
On that earlier-style counterweight, the "hook" at the end is "full open" when it is vertical and against the stop pin on the exhaust manifold. Easily seen. On the round counterweight in the later years, you might need to get under the car (on a secure lift!) and look at how the thermostatic spring is positioned on the shaft. Looking at things from under the car, block side of the exhaust manifold, the valve will move clockwise. From the fender-side of the manifold, it will move counter-clockwise from closed to open.
In the hot TX sunmers, the car started the same whether the valve was at 1/2 open or operated freely. In the cold times of the year, sometimes with snow, the automatic choke worked as it needed to, also. NO change between the stuck 1/2 open or "free movement" conditions. This was back in the "from '67 onward" times when gasoline was really gasoline, though. BTAIM
The LA motors did seem more inclined to coke-up the intake manifold's heat crossover, by observation. The local dealer sold a lot of LA Belvederes to elderly ladies in town. They usually drove to the store and to church, never long enough for the choke to fully release, so the heat crossover passage got clogged with carbon. So after a while, their cars would be at the dealership to get that carbon removed from the passage, manually. Never did see a B/RB motor needing the same thing, though.
Just my observations and experiences,
CBODY67
So, I had the dealer change it the last time. There is a brass (or similar) bushing which goes into the hole in the manifold, into which the valve's shaft is supposed to rotate. No problem putting the new bushing where the old one was, BUT when the shaft was inserted into it, the shaft moved reluctantly, in that the thermostatic spring could barely move the valve toward open at ambient shop temperature. The fix? To slightoy ream the inside diameter of the bushing so that the shaft fit freely into it and DID rotate freely when assembled. On the verge of a rattle, but it moved, which was what is needed. When the engine was revved a bit from hot base idle, the valve would open with the additional flow of exhaust gases.
Eventually, the valve stuck in the 1/2 open position again. As performance was NOT changed in that position, I just left it. NOR was cold or hot starting performance. A good compromise to me. Key thing was that there could be flow to the intake manifold so that the automatic choke thermostat would work as designed.
On that earlier-style counterweight, the "hook" at the end is "full open" when it is vertical and against the stop pin on the exhaust manifold. Easily seen. On the round counterweight in the later years, you might need to get under the car (on a secure lift!) and look at how the thermostatic spring is positioned on the shaft. Looking at things from under the car, block side of the exhaust manifold, the valve will move clockwise. From the fender-side of the manifold, it will move counter-clockwise from closed to open.
In the hot TX sunmers, the car started the same whether the valve was at 1/2 open or operated freely. In the cold times of the year, sometimes with snow, the automatic choke worked as it needed to, also. NO change between the stuck 1/2 open or "free movement" conditions. This was back in the "from '67 onward" times when gasoline was really gasoline, though. BTAIM
The LA motors did seem more inclined to coke-up the intake manifold's heat crossover, by observation. The local dealer sold a lot of LA Belvederes to elderly ladies in town. They usually drove to the store and to church, never long enough for the choke to fully release, so the heat crossover passage got clogged with carbon. So after a while, their cars would be at the dealership to get that carbon removed from the passage, manually. Never did see a B/RB motor needing the same thing, though.
Just my observations and experiences,
CBODY67
croderique
New Member
I presume from the pic attached the Manifold Heat Control Valve is closed so the flow goes back over the intake manifold to the drivers side exhaust. Correct?
It is frozen solid. I could not budge it. I will put some penetrating oil on it tomorrow and let it soak a while.
Thanks
Chuck
It is frozen solid. I could not budge it. I will put some penetrating oil on it tomorrow and let it soak a while.
Thanks
Chuck
Possibly . . . with a IR Heat Gun, you can start the engine and check to see what gets hot first. The exhaust manifold above the valve, below the valve, the exh pipe below the valve and . . . the heat crossover in the intake manifold at the choke thermostat and then on the driver's side . . . compared to the rest of the intake manifold.
Just because it is stuck does not mean it is in the closed position as the thermostatic valve realeases tension as the ambient air around the motor heats up.
You have a few choices and the bulk of them include taking the exh manifold off and putting it in a stout workbench vise and the use of a torch for heat. A "no heat" option with the manifold off and in the vise would include bending/deforming the valve so that it is more open than closed . . . on the stuck shaft. The valve is reasonably stout metal, so it can take some force to bend it.
Just some thoughts,
CBODY67
Just because it is stuck does not mean it is in the closed position as the thermostatic valve realeases tension as the ambient air around the motor heats up.
You have a few choices and the bulk of them include taking the exh manifold off and putting it in a stout workbench vise and the use of a torch for heat. A "no heat" option with the manifold off and in the vise would include bending/deforming the valve so that it is more open than closed . . . on the stuck shaft. The valve is reasonably stout metal, so it can take some force to bend it.
Just some thoughts,
CBODY67
croderique
New Member
Thanks. I tried the IR gun. The manifold heat valve heated up to 225F degrees and stayed there. The other side was about the same the same distance down. The exhaust pipes, about 4” from the bend on both sides, were about 125F. The stock cast iron intake manifold was all over the place depending on where you pointed. From 125F to 225F. Where the crossover was located was about 150F. The counterweight doesn’t move but seems to me to be open. Correct?
Interestingly the AFB carb on the passenger side was over 200F at the float bowl. The drivers side was 125F. I ordered an Edelbrock Heat insulator gasket 9266 but it didn’t fit an AFB so I reordered the correct one and should be in next week.
Chuck
Interestingly the AFB carb on the passenger side was over 200F at the float bowl. The drivers side was 125F. I ordered an Edelbrock Heat insulator gasket 9266 but it didn’t fit an AFB so I reordered the correct one and should be in next week.
Chuck
Last edited:
Similar threads
