Exhaust manifold heat control valve

51Hudson

I was messing around with the Hudson today and I noticed that the spring that is on the side near the bottom of the exhaust manifold is broken. I looked in the manual and I believe it called it the heat control valve. What does it do and how important is it? Is there replacement parts for it? Thanks

Marconi

Depends on what kind of a climate you live in. Cold climate it's pretty important, warm climate not so much. The shaft has a valve, flapper inside that turns as the engine warms up. When the engine's cold it directs most of the exhaust to the bottom of the intake manifold and helps to warm it up. As the engine warms up it opens and directs the exhaust to the exhaust manifold directly. Open in cold weather and you have a balky 'cold blooded' engine. Closed in warm/hot weather it can cause the engine to run hot/ overheat and do other damage.

51Hudson

Thanks for your reply. It gets cold around here in the winter but the 51 will be parked. It will be driven in the spring, summer and fall. I guess the coldest it would be driven is 45 degrees but not much. It would be mostly driven at 60 or above. Do you know if there are replacement parts? I also broke when messing with it was a metal tab that went threw the shaft and I guess proberly stopped the shaft from turning too far.

Marconi

Try Jason at Vintage Coach, Tues to Sat 8am to 5pm. 909-823-9168

Unknown

Having a broken spring on the manifold heat dampener can contribute to the shaft freezing in place with rust. The spring creates backpressure against which the exhaust moves the flapper there-by causing the shaft to move in the bushings that support it. With a broken spring... the flap dampener will tend to stay in place creating the opportunity for rust on the shaft therefore causing the dampener to be stuck in one position. Obviously if the dampener is in the closed or nearly closed position this will cause exhaust backpressure all the time. Hudsons that spend months in storage are prone to have a stuck heat dampener.

51Hudson

Well I called Jason today and he has a used spring he is going to send to me. I'm just glad I can get one so I can make it work right. How do I know if the valve is open or closed? Also when I put the spring on, is the valve suppose to be open or closed? Thanks for all of your help.

schillaz

here are some quick pix, the first one is of the valve closed. The second is where i am manually holding the valve open.

Closed:



Open:



Hope that helps.

51Hudson

Thanks for your help and the pics. They help a lot. I have another question for you guys that hopefully makes sense. When I get the new spring, do I have to put it on the valve shaft and "crank" the spring around the shaft before I let it sit against the stop pin. I hope that makes sense because I don't know how else to explain it.

Geoff

Yes you do. These springs are designed to hold the valve closed whilst the system is cold, and as they heat up the spring loses it's tension and allows the exhaust gas pressure to open the valve. As they cool down they regain their tension. Weird!

51Hudson

Geoff C., N.Z. wrote:

Yes you do. These springs are designed to hold the valve closed whilst the system is cold, and as they heat up the spring loses it's tension and allows the exhaust gas pressure to open the valve. As they cool down they regain their tension. Weird!

Thanks. Do you know how much tension I want to put on that spring before I set it in place?

51Hudson

Well I got my spring yesterday and it looks a lot better than my old one. I guess I am going to use the pics to try to see how much tension I want to put on the spring.

51Hudson

Well I think I got it figured out. Once you align the spring, you have to bring it around quite a bit to get it on the resting post. I think it is enough tension on it. I was taking the old one off and part of the spring is stuck in the slot. I will hopefully get that out tomorrow.

51Hudson

Well I put the spring on today. The first time I put it on the spring didn't have enough tension on it. So I took it off and put it on so it had some more tension on it. There isn't much of choice on how much tension to put on it, so I hope it is good. It stays closed and if you rev the engine it opens but will close when you let off the gas. I didn't run it long enough to see if it stayed open once it warmed up.

TOM-WA-

Just my 2 cents, but the entire concept of the Heat Riser and the spring is only appropriate if you live in a colder climate and use your car as a daily driver.

My spring was broken and I didn't realize that it was allowing the hot exhaust to always escape to the carb. I'd get maybe a mile down the road and the gas would vaporize and the car would not run.

Sooooooo.. I live in Seattle, but do not drive my car in the winter....sooooo I just disabled the entire contraption and even tho it is sometimes a tad more difficult to start I have never stalled again.. I suspect that this could also be the cause of what some think is VAPOR LOCK......same symptoms

51Hudson

Does anyone know if it is suppose to stay open even at idle when it gets warm? I didn't run it much but if you gave it gas it would open but as soon as it idled again, it would close.

EDIT I forgot to add earlier that the little stopper piece that looks like it hits the metal post when the valve is closed is not hitting the metal post when closed. It is off by an 1/4 of an inch. I don't know if that stopper is important. It almost looks like it acts like an spacer for the spring and that end piece that holds everything on the shaft.

RonS

It is my understanding that if the spring is correctly installed with tension, the valve will close when cold and then as the engine warms, the spring expands over coming the weight & opening the valve to full flow out the exhaust. If the spring is removed from the stud (or roll pin) the valve has a weight that will "default" to open. When connected,the problem is, as the engine cools the valve can stick open and be a pest. Worse, when parked, is can stick closed from the last "cool down" and not open as the engine warms. Similar to stuffing a potato in the exhaust pipe. Some one earlier stated, it will replicate vapor lock. These should be checked for free movement.

51Hudson

RonS wrote:

It is my understanding that if the spring is correctly installed with tension, the valve will close when cold and then as the engine warms, the spring expands over coming the weight & opening the valve to full flow out the exhaust. If the spring is removed from the stud (or roll pin) the valve has a weight that will "default" to open. When connected,the problem is, as the engine cools the valve can stick open and be a pest. Worse, when parked, is can stick closed from the last "cool down" and not open as the engine warms. Similar to stuffing a potato in the exhaust pipe. Some one earlier stated, it will replicate vapor lock. These should be checked for free movement.

Thanks for you response. The spring is actually holding the valve shut. You say the spring expands when it warms up. Does that mean it weakens when it warms up so the weight will move it to open? The valve opens and closes with no problem with nothing on it. But when I put the end piece on that actually hold the spring form coming off, it gets a little harder to move but not bad.

[Deleted User]

The spring is there to keep the valve closed when cold, and as it warms up the hot exhaust lets the spring warm up and the valve open a little at a time will driving over 5 miles per hour, and the faster you go it opens more, but when you drop to an idle it will close, hit the gas and it opens but will never open and stay open while driving. Your foot on the gas pedal controls the spring. Do your self a favor, get rid of it and increase your mileage and less vapor lock problems. Walt.

[Deleted User]

Amen

Lee ODell

I once had a car without exhaust damper. When I installed one, the performance dropped. The damper was restricting the exhaust. Of course living in sunny/sometime rainy Calif I really didn't need one so off it came. Better performance.

Lee O'Dell

51Hudson

walts garage-53 wrote:

The spring is there to keep the valve closed when cold, and as it warms up the hot exhaust lets the spring warm up and the valve open a little at a time will driving over 5 miles per hour, and the faster you go it opens more, but when you drop to an idle it will close, hit the gas and it opens but will never open and stay open while driving. Your foot on the gas pedal controls the spring. Do your self a favor, get rid of it and increase your mileage and less vapor lock problems. Walt.

Thanks. So it sounds like mine is working right then. But now after reading this, I may just remove it. If I remove it, do I have to do anything to keep it open or will it just stay open?

[Deleted User]

You have 2 ways to do this. One, wire it wide open but it will still restrict the exhaust flow. Two remove the manifold and grind the shaft in half, remove it completely, and drill and tap for pipe plugs on both sides. Do not try to chisel it off as you can break the manifold as it's cast iron. Work involved here. Start by wiring it open. The heat valve is one reason the manifolds cracks at number 3 and 4 cylinder exhaust outlets. Walt.

RonS

WALT, If I disconnect the spring on the heat riser valve, won't the valve stay in the open position. I know the best way to be sure, is to remove it completely, but that is not an option now. Why wire it open, won't the weight hold it open?

[Deleted User]

No, it will not stay open. You must wire it open, for every time you remove your foot off the accelerator, it will suck the valve closed. And if it gets really hot it will get stuck shut. Wire it and forget it. Walt.

RonS

I was afraid you would say that. Thanks

superwasp

So, I know I'm resurrecting a long-dead thread but the pictures Shillaz posted in 2011are gone. Is this the correct orientation of the spring?

tigermoth

Why not focus on the wire it open a and forget it portion of the revised thread?

regards, Tom

superwasp

It was previously wired open and ran like absolute crap until fully warmed. Even fully warmed it would stumble a little. Once I reinstalled the spring it ran much, much better. I know the popular thing is to wire open, but that scenario didn't work for my application. For reference, the install above is correct.