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1956 Chevy 3100 restoration (attempt) - what is this "choke like" feature or item inside the exhaust manifold? How important is it?

Mine is froze in the open position and I am attempting to slowly break it loose with Blaster and small hammer so it will operate, for whatever purpose.

Better than frozen shut.

It closes to provide early heat to the intake manifold. Once warmed up, it opens. But it sounds like you are missing the coiled spring that connects to the end of the shaft ex̌ternally which controls opening and closing.

That flap valve is known as a "heat riser"- - - -During engine warmup, it directs exhaust gas against the bottom of the intake manifold to help keep the gasoline vapors from condensing back into a liquid and prevent uneven fuel/air mixtures in the cylinders. Once the engine coolant reaches normal operating temperatures, manifold heat is not needed, so a coiled bimetal spring on the shaft relaxes and the counterweight causes the flap valve to open. Using a torch and some penetrating oil, and tapping the shaft fore and aft repeatedly is the best way to free it up without damaging anything. Be patient- - - -it's taken me a couple of hours and repeated heat/tap/repeat cycles at times to free up a heat riser! This spring works well as a replacement, and it's a fraction of the cost of an OEM stovebolt item:

www.ebay.com/itm/182196172425?

Jerry

The spring is present and appears to be in good condition though there's some rust present. I've cleaned the spring, the flap and insides. So, now it is just a matter of doing some tapping and heat. I will try the heat mainly around the entry shaft on both sides, inside and out.

Thanks for the identification and need for the heat riser. I will get busy to see if I can free it up.

Hawkman - When you put some heat to the manifold at the shaft locations, give it some shots of penetrating oil like Jerry suggests (WD-40, Kroil, etc.) while it still hot. The heat and cooling of the pieces will help draw the lube in to help break the rust bond.

A home brew of acetone and automatic transmission fluid in a 50/50 mix is just about as effective as KROIL at a fraction of the price, and Walmart has both ingredients in stock. Use the bottom shelf house brand ATF- - - - -it works just as well as the expensive stuff!
Jerry

Hotrod Lincoln's suggestion is spot on. I love using the home brew.

The heat riser on my '54 235 in my '46 1/2 ton has been stuck open for 40 years (literally). Takes a bit longer to warm the engine when cold, but I haven't noted any adverse effects. Put 92,000 miles on that engine since full rebuild in 1986. Just never got around to fixing it.

Another slick trick to free up rust-seized parts such as a heat riser is paraffin, candle wax, or beeswax. I keep a few blocks of fruit jar sealing wax from the canning supply aisle at Walmart around my gunsmithing/reloading shop and some in the engine shop also. Warm up the rusty part with a torch until it's too hot to touch, and apply the paraffin block to the threads or tight fitting bits and pieces. It sticks around and penetrates better than oil does.
Jerry

UPDATE: Sound advice from you all. I pointed out to my son what I was having problems with on the heat riser. He's been helping me on my project while I help him on his. In any case, he started working the heat riser with rubber mallet and Blaster juice. After about 20 minutes, he had it working like a charm. Now it will move with the spring action like it should. Next time I get a chance I will be getting some beeswax type product to have just in case.

Here's a supply that will last you for several years. I also use the stuff to flux the lead I use to cast bullets and fishing sinkers with.

www.ebay.com/itm/206384112640?

Jerry