Heat Riser Valve and Exhaust Manifold Tube

[Barry Wolk]

This is what I've garnered from the Mark II encyclopedia. There were lots of choke updates. None of them included running a pipe from the exhaust manifold to the carb. In fact, they were quite emphatic that exhaust gasses were no NEVER enter the carb. The result would be lots of carbon deposits and an inoperative choke.

It helps to understand the way that the warm-up system on the car works. The first step is the thermostatically controlled damper on the passenger side exhaust. The operation of this valve is essential to the system working properly. It basically senses underhood temperature, not the temperature of the pipe. Leaving the hood open to test will give you a false reading.

Check to see that the damper is closed when the engine is cold. The spring is easy to install backwards, defeating the operation. The circle on the axle of this valve is actually weighted. It rotates when the bi-metal spring relaxes as it warms up.

The valve is designed to create hot exhaust back pressure when the engine is cold. There is a passageway underneath the carb, cast into the intake manifold. It connects two ports in the heads that connect to the exhaust passages. Gasses, like water and electricity, follow the path of least resistance. Blocking one exhaust manifold forces that bank's exhaust back through the passages, under the carb to help vaporize condensed gas, through the other head to warm it up and out the driver's side exhaust pipes. If it were not for the crossover pipe in the exhaust, there would be nothing coming out of the passenger side tail pipe. This is why there's a plume of steam coming out just the driver's side, for a time, when it's cold.

As the space under the hood warms up the engine has reached a proper temperature where gas no longer condenses on the cold manifold surface the valve is allowed to open under the offset weight of the damper. This allows exhaust to flow out of bot sides equally.

The book spoke of two tubes on the carb. Neither of the two tubes are to hook up to exhaust gasses. What they do hook up to is a tapered tube that passes through the hot exhaust gas chamber beneath the carb. Internal porting draws air from within the carb, through one side tube, through the tube in the exhaust chamber, up through the other tube and into the choke chamber, moving a bimetal spring. The hot air is then drawn back into the air/fuel mixture. Exhaust gasses were never intended to pass into the carb under any circumstances.

It looks like the tube with the box on the manifold is a logical fix instead of drilling out the tube in the exhaust passage. The tube would pick up hot air through the box on the manifold and pass it through to the choke mechanism directly.

Does the hose from the manifold pass through some type of heat exchanger, or right to the choke? If it went to a heat exchanger, that would be more complicated, but it would work.

[Don Henschel]

Also about that heat riser valve, they can seize in the closed position which is probably worse! They should be checked once in a while when the engine is cold so you don't burn your fingers. Just grab that balance wheel Barry mentioned and try to turn it. It should turn freely with the resistance of the bi-metalic spring forcing it closed. Spring resistance should be felt indicating that the spring is not broken. If it is seized, soak the shaft with penetrating oil and carefully try to work it loose without twisting or bending the shaft.

[depmike38]

Don, which way should it rotate with a cold engine? Also, personal favorite for freeing anything stuck is a penetrating oil called Kroil by Kano Labs. It will get into and break loose just about anything with a little patience & no, this was not a paid endorsement though I"ve recommended them so much they should pay me.

[Don Henschel]

Mine rotates clockwise looking at it from the rear as it faces the firewall. I use liquid wrench as it is very thin (And is refered to as a penetrating oil not a lubricant)and it looks like it might even have grafite mixed in it as well. Mine has the valve cut out but I found a 57 Capri with both exhaust manifolds laying in the empty engine compartment with a good heat riser still on. It looks the same. When I take them apart to clean and repair them I use grafite never seize on the shaft and bore and that seems to last a long time.

[Shelly Harris]

Check to see that the damper is closed when the engine is cold. The spring is easy to install backwards, defeating the operation. The circle on the axle of this valve is actually weighted. It rotates when the bi-metal spring relaxes as it warms up.

My damper is closed when cold and by hand I can freely move it through it's axis. When cold the spring brings up the weighted side nicely and hold it up thus closing the exhaust. As I said it seems to rotate nicely by hand. However, after warm up the spring never relaxes and the weighted side doesn't fall back... there is a little bit of resistance when I turn it down by hand.
1. Is it possible that the spring has lost it's ability to relax when hot and

2. I squirted some WD on it to get it moving freely but the heat cooks that away and it gets that resistance I mentioned...what to do to lube it or??

Thanks for responses

[Barry Wolk]

Shelly, try to unwind the spring by one turn.

This is the correct position for the damper weight when cold.

http://i244.photobucket.com/albums/gg18/barry2952/1%20Mark%20II%20docs/IMG_3601.jpg

This is the correct orientation of the spring when cold.

http://i244.photobucket.com/albums/gg18/barry2952/1%20Mark%20II%20docs/IMG_3602.jpg

[Shelly Harris]

Thanks for the pics..... I spray some "Liquid Wrench " on the pivot points and that mey work better. I don't think I can unwind the spring... it fits very nice the way it is. Probably won't be able to get back to the car till Saturday... I stay downtown while on trial.

[Barry Wolk]

I don't believe you should use any lubricant on this device, graphite or otherwise. The residual oils or carbon will simply gum things up quicker.

The best thing is to simply exercise the joint while cleaning it with carb cleaner. Then use compressed air to blow the loosened dirt and carbon inward. repeated applications and working of the axle should make things work properly without lube.

[Nick DeSpirito]

I think I might be missing that little spring on the other side. What does it do and where can I get a new one?

[Barry Wolk]

It's just an anti-rattle device. A trip to Home Despot's hardware section should provide the necessary replacement. It's a very weak spring. Here's a scale picture of it.

I mic'ed the spring wire at .017.

http://i244.photobucket.com/albums/gg18/barry2952/1%20Mark%20II%20docs/IMG_3609.jpg

http://i244.photobucket.com/albums/gg18/barry2952/1%20Mark%20II%20docs/IMG_3608.jpg

[Nick DeSpirito]

Thanks Barry. I'll give the Depot a try.:)

[Barry Wolk]

Now I have to go put it back on the car before I lose it.:rolleyes:

[Don Henschel]

I don't believe you should use any lubricant on this device, graphite or otherwise. The residual oils or carbon will simply gum things up quicker.

The best thing is to simply exercise the joint while cleaning it with carb cleaner. Then use compressed air to blow the loosened dirt and carbon inward. repeated applications and working of the axle should make things work properly without lube.

Thats why I don't use WD-40. Too much oil in it which cooks. Liquid wrench seems to be "drier" after it disolves the rust and dries up.

[Shelly Harris]

I thought I had a leak in the right side exhaust manifold, but it turns out to be a crack. There's no such thing as getting a new one, so fortunately Jack still has some on his wrecks and will be sending one out to my mechanic this week. So when Jack's are gone, good luck! Interestingly he says that it's the right side that's cracking more often than the left (driver's side) and he suspects it might have something to do with the heat riser on the passenger side. I have mine permanently stuck open as I have an electric choke on the Carter carb, but all of you that have the heat tube arrangement on the choke (which is one of the reasons to have a heat riser on the exhaust) might want to consider permanently keeping that heat riser open or remove it. This is a speculation of course, but take it for what it's worth.

[Nick DeSpirito]

It is also, because of that valve, that the right side exhaust rusts faster than the left.

I had to replace the right rear exhaust pipe, muffler, and crossover pipe two years ago. There was also a pin hole in the right snorkel pipe which they welded closed. Condensation seems to build up on the right leg of the system and I suspect it is because of the manifold valve. The rest of the system, which I bought from Jack when I was restoring the car, has been on the car since '89-'90 and is still in good condition.

Of course, if your system is stainless, you need not worry about this.

[Roger Zimmermann]

....it might have something to do with the heat riser on the passenger side. I have mine permanently stuck open as I have an electric choke on the Carter carb, but all of you that have the heat tube arrangement on the choke (which is one of the reasons to have a heat riser on the exhaust) might want to consider permanently keeping that heat riser open or remove it. This is a speculation of course, but take it for what it's worth.
In my opinion, the heat riser and the tube for the choke are two unrelated different systems. The heat riser allows the exhaust gases to heat the carb, allowing a better evaporation of the fuel when the engine is starting from cold.
The heat tube is needed on cars still having the choke actuated with a bi-metal.
Without a heat riser, the tube choke is still needed to let open the ckoke. If the car has an electric choke, the heat riser is still doing the job it was intended to do.
To resume: both systems were created to help drivability with a cold engine; their action is however different.

About the RH exhaust system rusting more than the other side on cars equiped with a heat riser: during warm-up, almost all water resulting from the combustion is going out at the RH pipe. If the distance travelled is not sufficient, this corroding water is still resting in the tubes, doing it's nasty work.

[Shelly Harris]

In my opinion, the heat riser and the tube for the choke are two unrelated different systems.

Yes, I agree they are different systems. However, what I am suggesting is that the standard auto choke is dependent on the heat tube to function and the heat riser's function is to get a faster warming of the engine at start up. So the heat riser has a direct effect on the choke. Since I have an electric choke and have trashed the heat tube stuff, my engine no longer needs a faster warm up to release the choke. Thus one less reason for a heat riser and it's suspected damaging effect on the exhaust manifold.

[Keith W Colonna]

Hello Group,
There is a high temp graphite spray which is almost designed for this application. The solvents will not evaporate with heat, there is no oil to gum up, the graphite provides continual lubrication.
It is available at most auto parts stores.
But, first...clean out the area as advised in previous posts.

[Barry Wolk]

Gerome PM'd me about his choke tube. I've decided to respond here.

I'll explain what the manifold tube is for. There's a passage under the carb that gets a flow of hot exhaust gasses when the automatic damper on the passenger side exhaust is closed. This warms the fuel, helping it to vaporize it on cold start-up. The tube we're speaking of passes through this chamber that's surrounded by hot exhaust gasses, but they can't get through a good tube. The tube allows vacuum to suck just hot air through the tube. This hot air is sucked into the carb by the vacuum that's created by a running engine. This hot air is passes through the choke mechanism, bending the bimetal spring that opens and closes the air flow on startup. That works to richen the mixture to keep the engine running until the heated manifold can properly vaporize the fuel. That spring also works to set the fast idle cam that does what the name implies. At the point of warm up, the bimetal spring opens the choke plate, allowing the engine to breath normally, automatically correcting the air/fuel mixture to an efficient ratio. Tapping the accelerator releases the fast idle cam and the engine rpm drops to normal. When the engine compartment warms up the bi-metal spring on the exhaust damper opens, letting hot exhaust gasses pass normally through the passenger-side exhaust pipes and stopping the flow through the manifold. By this time the whole engine has warmed up, vaporizing fuel properly on its own.

Your tube failed, allowing hot exhaust gasses to flow into an area that wasn't suppose to have anything but hot air. The excessive heat of exhaust being drawn into the carb is what wrecked yours. You would likely not have had a fire had you caught the perforated tube in time.

Now, your question to me was about a procedure to replace the tube, and frankly, I don't know, as I've never done one. Can someone describe the procedure for Gerome? Can it be done without removing the manifold? I know it's a tapered tube and can only go in one way. What are the chances of getting it out while the manifold is installed?

From my perspective, I would replace the intake manifold gaskets anyway, as they are a prime source of vacuum leaks. It will be maddening to install a rebuilt carb only to have to take it off to fix vacuum leaks. Use the vacuum gauge method as described by Pony and it'll run like a top.

Can someone advise Gerome about tube replacement?

[Gerome]

Thank you Barry.

Work is being done by a mechanic as this is all beyond my means...however, ALL related suggestions will be relayed to him, and luckily he's not foreign to these & other Lincolns.

[Nick DeSpirito]

Gerome,

I replaced mine back in the nineties. The intake manifold came out and I used a punch the remove the choke tube while it was on the work bench. I can't see anyone getting it out while the intake manifold is on the car, especially if yours is breached and rusted out. It will probably come out in pieces.

Barry is right. One side is larger than the other, so it can only go in one way. If I remember correctly, the ends are round, while the middle is triangular shaped.

Hope this helps you. :)

[Pat Marshall]

Here's a good look at one them!

[Gerome]

OK, thanks...will share!

[Roger Zimmermann]

Barry, your explanation how the whole system is working is excellent! Many people don't understand this basic function. I doubt that the engine could burn because of that broken tube; by the time the gasses arrive at the choke bi-metal, they are colder. But the agressive by-products and carbon are blocking/letting rust the mechanism; I saw that on some Cadillac carbs which are using a similar arrangement.
I replaced a couple of time the tube from Cadillac's intake manifold; it cannot be done when the manifold is on the engine. Most of the time, you have to "fish" the remains of the tube; the inlet/outlet for the tube are very near of the cylinder heads, preventing a good view of the whole matter. If you have to drill the tube, a hand held machine will not do the job.

[Barry Wolk]

Roger, what I tried to project is that the wrecked choke could easily have made the car run poorly, causing the car to backfire and ignite spilled fuel. I have seen a number of melted choke housings from this problem.

I'm glad you liked my description. It is true that many do not understand that all elements of the system must be operating correctly to function trouble-free.

[Roger Zimmermann]

Roger, what I tried to project is that the wrecked choke could easily have made the car run poorly, causing the car to backfire and ignite spilled fuel. I have seen a number of melted choke housings from this problem.


That the worst case scenario I never saw! I agree that in such situation a fire could occur.