The Stovebolt Site Forums The Shop Area Engine Shop How To Free Up The Damper On A Exhaust Manifold

Any ideas on how I can keep the damper freed up on a 1942 Chevy 6 cylinder truck 235 exhaust manifold. Thanks for your help!!!!!!!!!!!! 1-262-392-2989 or [email protected]

Marv.

PB Blaster and gentle tapping with a small ball peen hammer. If it's already loose and you just looking to keep it free a little penetrating oil now and then should help.

Good morning Marv.

I found on my '36 pickup that penetrating oils and tapping as suggested by Martin are a temporary fix at best. The permanent solution that I implemented about 35 years ago was to make a shaft for the valve from stainless steel and I also put stainless steel bushings in the exhaust manifold casting. That has permanently solved the problem and I still have the '36.

For what it's worth, I had one that I couldn't free up with any amount of soaking, tapping, or heating with a MAP torch. I'm sure someone more determined could have with a proper torch and tools. Finally gave up and robbed from a spare engine core that had a free heat valve.

It helps to remove the intake manifold when doing the Kroil/tapping technique so that you can get to both the inside and the outside of where the shaft enters and exits the exhaust manifold. My hunch is that the jamming happens more from the inside out than the outside in, so approaching from just the outside might not work. The inside can be caked with carbon deposits, so it also helps to take a small chisel or screwdriver to clean the both sides on the inside where the shaft goes through the manifold. Try to get the shaft and the manifold down to bare metal on the inside so that the Kroil can do its thing.

I'll shoot them with Kroil and tap them a few times a day. They can take several days to break free, so be patient. You'll feel some play at first when you tap the shaft as it moves side to side, then you'll finally feel the baffle move a bit when you twist the weight. Once it starts to twist, they tend to break free with one or two more treatments.

You don't have to be too gentle when you tap, but don't be a gorilla either. There is some lateral play the way these things are designed, and you are trying to take advantage of that by tapping to break the jam with side to side movement.

I'll give mine an occasional generous shot of Kroil or Blaster whenever I have a can out to do something else under the hood.

Good luck,

Matt

Carbon is what jams them up. Once you break the carbon loose with Kroil and several taps with a hammer, it should become loose enough to function properly for another 50 years.
Taking it apart and replacing the shaft is not the easiest of undertakings. To replace the shaft, you will need to do a lot of stud and bolt breaking to get to the flapper. Then you will need to separate the flapper from the shaft. Then you will need to weld the steel flapper back on to the stainless steel shaft. This will require a TIG welder for an easy to do good weld.
I would reserve the replacement of the shaft for when there is a lot of slop between the manifold and the shaft, or for when the slotted end is broken, preventing you from putting the spring in place.
Carl

Marvin, if it don't break free pretty soon just bite the bullet and "do it once do it right".

Mine was all screwed up so I pulled it apart. Take a picture, or make a mark somehow of just how it looks and goes back together. Then I took a dremel tool and ground off the little spot weld on the flap so I could get the stem out. The stem slot was broken and needed replacing anyway.

I drilled out the little "pin" that holds the stem into the weight and pulled the old stem out. NOTE: at this point I found bushings in the manifold that were worn in half. Now if bushing was from the factory, or someone years ago put the bushing in, I'm not sure. Looked original to me but that is a different story which has already been beat to death!!!

A trip to ACE Hardware got me the rod to use for a stem and the bushings that would fit the stem and the manifold holes which I drilled out just a tat to put in the brass bushings. Cut a slit in the stem and ordered a new spring from Jim Carter. Once all back together I looked at a job well done and had a hot dog and a cold Pepsi. It is not a hard job and it works well.

Oh, I also drilled out the "pin" that the spring goes on and installed a new roll pin......I have a few pictures of it on my photobucket page, in the 50 coupe album, but if you click on the link below I don't think you can see it......... Good luck. Let us know how you come out.

Thanks for all the reply's so far!!!! I think my problem is rust no carbon if the truck sits for a long time over winter it is froze up in spring. Also once it get hot the same thing happens. What would be the problem with just leaving the damper open?????

Marv.

Manifold heat valve? Were these optional equipment? Do we all have these?

Some folks throw them away and plug the holes. The "flap" routes the hot exhaust back upward to heat up the intake manifold for better combustion. Once the engine is hot it makes no difference...... just my penny version!

Wally, I've not seen one from the factory on our pickups that did not have one at least in the beginning......but I could be wrong!

All downdraft carburetor 216/235/261 engines had one.

If you live in a mild climate, you can get away without a fully functional heat valve as long as it is jammed up in the closed (warmed up) position.
The OP lives in Wisconsin. He needs a fully functional one 6 months of the year. (Only 2 seasons in Wisconsin. Winter and pothole repair season.)
Carl

"To replace the shaft, you will need to do a lot of stud and bolt breaking to get to the flapper."

Good morning Carl. Although I did that job about 35 years ago I don't recall having any problems or breaking anything. Simply removing the manifolds as a unit then loosening the nuts on the 4 studs that hold the manifolds together gave access to the heat riser plate.

"Then you will need to separate the flapper from the shaft."

I'm not certain after all this time but I recall the "flapper" being riveted to the shaft on my '36 pickup.

"Then you will need to weld the steel flapper back on to the stainless steel shaft. This will require a TIG welder for an easy to do good weld."

When I did mine I had only an AC "buzz box" welder. That welds stainless no sweat using 316 stainless electrodes. I now have a tig and have that option also.

As Achipmunk points out doing it once and doing it right is a concept with merit.

I have done 3 of them locked up solid with Kroil and a hammer. All of them just once. I consider myself done on all 3 of them.

If you separate the manifolds, make sure to tighten them to the head before final tightening of the manifold through bolts.

Ed

"I have done 3 of them locked up solid with Kroil and a hammer. All of them just once. I consider myself done on all 3 of them."

You had much better success with the hammer and lubricant method than I did Carl. I don't know if Kroil existed when I did the stainless steel shaft and bushing conversion in about 1980. Anyway, as usual, there are various approaches that work.

"If you separate the manifolds, make sure to tighten them to the head before final tightening of the manifold through bolts."

Ed, good point. If that is not done the manifold flanges may not align properly.