VCCA Home Forums TECHNICAL - 1945 AND NEWER 1949-1954 52 chevy 235 stuck exhaust manifold heat valve

Does anyone know how to tell the position of the heat valve by the balance weight position? My balance weight is horizontal. I am guessing that this means that it is open which is bad (I think). I have used Deep Creep, WD-40, kerosene and baking soda (shop manual suggestion) over the last several days with a small hammer w/o any luck. I am about to order some Kroil. Any suggestions on how to unstick it w/o taking the manifold off would be greatly appreciated.

John

You will have much better luck if you remove the manifold. This will allow you access to the back side of the shaft from inside so you can soak it with any of the suggested products.

The shaft is SS. Careful with the butterfly inside. I would suggest a hot wrench at the point where the shaft enters and leaves the manifold. Careful with the hot knife, but patience and a small hammer will produce results.

With the weight in the horizontal position the heat is "on" as it would be for a cold engine.

John,

As it happens, I just, today, finished up and road-tested a repair to the manifold heat damper on my 40 1/2 ton pickup (with 216 engine).

Mine was stuck, and I didn't know what position it was in. Since I had an exhaust manifold gasket leak anyway, I figured it would be best to remove the manifold assembly to inspect and repair the heat damper. I decided to split the manifold assembly at the plenum chamber joint so I could get a good look and better access to the damper and shaft. The four studs/bolts were so badly rusted that after breaking one, I simply sawed the others off. This, of course, requires drilling out the remaining stubs and retapping the holes. If you don't have access to a drill press, I don't recommend trying this, as it will be difficult to drill the holes true and straight with a hand-held drill. If your new holes are off center or not straight, you'll have a tough time lining up the studs or bolts with their matching holes in the opposite manifold. In any case, it's probably not necessary to split the intake/exhaust manifolds in order to free up the heat damper.

After disassembly of the manifolds, I could see that my damper was stuck in the half-way position. I began by spraying the damper shaft on both sides of each end where it penetrates the plenum chamber with PB Blaster, which is probably the best rust penetrant on the market, and is readily available at Lowe's, Home Depot, etc. After a few minutes, I put a little torque on the damper shaft using the counterweight, but I could see it wasn't going anywhere. I noticed there was about 1/16" of lateral clearance between the damper and the inner walls of the plenum, so I thought I might be able to tap the damper shaft laterally with a hammer. After a few tentative taps, I noticed the shaft moving. Once it starts moving, the penetrant begins to work even faster. I tapped the shaft back and forth several times, and then I was able to begin rotating the shaft gradually back and forth until it was traveling in the full arc of about 45 degrees. After more dousing with PB and more rotating, the shaft was soon completely free and would spring back to the "heat on" position when released from the "heat off" position. I then lubricated the shaft with WD40. By the way, if you're standing on the left side (driver's side) of the engine looking at the heat damper counterweight, when in the "heat on" position (engine cold), the counterweight will be rolled out toward you so that the flat portion of the counterweight is horizontal. When the shaft is free, you should be able to roll the counterweight in toward the engine block in an arc of about 45 degrees. In this position, the counterweight is out of sight under the intake manifold. When you release it, it should spring back out to the "heat on" position.

After reassembly earlier today, I drove the truck for 20 miles at 50 mph, then stopped to check the heat damper, and sure enough, it was rolled in under the manifold in the full "heat off" position. Within a half hour of getting back home and shutting the engine down, the damper had returned to the "heat on" position. Several hours later, while writing this post, I went out to check the damper orientation and discovered that the damper shaft was already beginning to bind up again. I squirted it with some PB and it freed right up, but I can see I'm going to have to keep a close watch on this and lubricate it regularly. PB or WD40 burns off right away, so they are not the best in-service lubricants. I think the best lube for this application would be an aerosol-born high-temp molybdenum-sulfide anti-seize lubricant.

Good luck with your repair.

Mark Yeamans
VCCA# 35724

Thank for the info.

I suspected that it was in the "on" position. As for lubricants, I have ordered AeroKroil to unstick this thing and some Penophite (penetrating oil w/graphite) for lubricant which is supposed to be good to 600 deg. F. Both are from Kano Labs. Kano Labs also sells pyrolube which is for stuff operating in kilns and is supposed to be good to 1800 deg. F but it is pretty pricey. I may just try the normal anti-seize stuff (some type of silver stuff w/ graphite I believe) that is supposed to be a good high heat lubricant up to 1400 deg. F. I'll repost if I ever get this thing unstuck.

John

I've used Kroil for this type of situations. spray a little, tap a little. after a few days the riser was free

Over the many years I've used Mark's method with good results. Tapping back and forth with a light ball pein hammer and using various penetrants. To keep it working I work never seize into both sides because the penetrants burn off quickly. The thermostatic spring should be replaced and they are available from suppliers.

Thanks for this thread. What are the symptoms caused by the heat value being stuck open?

I ask because mine is stuck open too. And I didn't even realize there was one until I started reading this thread.

A close friend and exceptional mechanic looked at the engine in my '49 Chevy 4400, did many tests that I had already done (measured vacuum, tested for vacuum leaks, checked the timing, measured tach and dwell, felt the exhaust and et cetera). He agrees that everything checks out except for the fact that the manifold heat valve is stuck open and the thermal spring is missing.

If a stuck-in-the-on-position manifold heat valve can cause an eratic miss it would explain a couple of things, like the fact that it doesn't miss when it's cold and only starts to miss as the engine warms up.

What symptoms does a stuck-on manifold heat valve cause?

Many thanks,

Lee Prairie

According to the shop manual "it will result in poor engine performance, overheating and detonation." I am not sure about a miss though. I do have a slight miss which I have been trying to diagnose. I have read the "erratic miss" thread which has a lot of good suggestions. I will be checking timing this weekend. I also suspect that the carb insulator may be bad. The intake manifold always has a little bit of gas on the manifold just below the insulator after I turn off the engine. I was going to put some gasket sealer between the insulator and the manifold to see if it would help before I get a new insulator.

My concern with the heat valve is the heating up of the intake manifold. This is just not good all the way around since this messes up the fuel charge to the engine and really bakes the insulator.

I just bought this car at the end of last year and I haven't been able to run it in the northeast since we have had pretty poor weather so far. I have checked everything else mechanically on the engine (plugs, wires, points, dist. cap, compression, etc.) and it seems to be fine. The timing, insulator, and heat valve are the last issues to tackle b/f I put it on the street.

John

What position is the weight in. Flat bottom perfectly horizontal or at about a 30 degree angle?
With a cold engine and to warm up the incoming gases it would be horizontal. When the engine is really hot it would be at a 30 Deg. angle.
In this cool weater it would take quite a bit ot get it hot enough to be full open. Under load the passing exhaust will help force it open....but not at idle.
If it is stuck its better to be at the 30 Deg. point. Will just hesitate more when cold. In the Summer will be very little problem.

In my case the weight is at an angle. The plane of the flat bottom is more verticle than horizontal. Perhaps it makes about a 30 deg. angle with the verticle. But it looks like it would be blocked from swinging up to the horizontal because the end of the weight would impact the manifold, unless it rotates the other way so that the flat part of the weight comes out on top.

It is stuck and doesn't budge - the thermal spring is missing, but it wouldn't work if it were not missing. Perhaps when it got stuck, the spring was off so it got stuck in the 'off' position????

Lee

The flat is at the bottom when cold. With the weight in your position the flapper valve is preventing the exhaust heat from reaching the incoming mixture. This is where it should be for a hot engine.

Lee,

A few months back, I posted a querry about a problem I was having with restarting the engine (216) in my 40 1/2 ton pickup after having been shut down for 15 minutes or so after having been thoroughly warmed up from driving. To restart the engine took a tremendous amount of cranking to dilute the fuel which had dripped down into the manifold after shutdown. I was unsure why the carburetor was leaking fuel into the manifold after shutting the engine down. There were many responses to my querry, and a lot of good info about the Carter W1 carburetors was posted. One of the suggestions was that a stuck manifold heat damper (I knew mine was stuck) could cause fuel "percolation" as a result of the carburetor getting too hot due to the stuck heat damper. This seemed plausible, as I had looked down into the carburetor after a hot shutdown and seen gas bubbles and droplets forming on the end of the feed nozzle and dropping down into the manifold.

Yesterday, I freed up my stuck heat damper and test-drove the truck to verify that the damper was operating properly, which it was. Today, I took the truck on a 200 mile trip, and performed numerous hot re-starts during the trip. In each case, the engine fired up immediately on cranking under the same conditions in which previous to the repair would have required excessive cranking to start. So, I'm nearly 100% convinced that one possible symptom of a stuck manifold heat damper (assuming it's stuck in the "heat on" position") is that the carburetor can get too hot, resulting in the gas in the float bowl boiling and percolating into the venturi after the engine is shut down.

Mark Yeamans
VCCA# 35724

Finally got the valve unstuck.

TIP: you must tap the valve from both sides. I originally thought that it was just stuck, so I was only tapping it from the firewall side. This was just jamming the valve up against the inside of the manifold. I used an 5" aluminum rod about 3/8" in diameter (from an old wind chime) as a punch. This is the perfect length to get to the valve from both sides since it clears all of the stuff on both sides that you do not want to hit with the hammer like the oil pressure sending unit line or the intake manifold. I am sure that a brass punch of equal length would work as well.

It only took about 10 taps on each side to get it so that it could be rotated. I then used carb cleaner to free it up completely since this is best for cleaning carbon and was recommended on a Corvette site that I found. It worked quite well. I put heavy duty anti-seize on it to keep it free. I have seen shop manual recommendations that say it should be checked once a month.

Now to give the car a coat of wax and take it out for a spin!