Packard Forum Index » Pre-War (1899-1942)

Can someone please explain to me what this hole is for
on the top of my exhaust manifold

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That is for the heat tube to go into the by-metal choke. As the by-metal is heated the the coil tightens which opens the choke. when the manifold cools the coil relaxes and closes the choke. Mine is also missing on my 49. Has anyone out there made one?

It looks like the end of the heat stove. That is a tube pressed into the exhaust manifold in such a way the hot exhaust gas surrounds and heats the tube. The bottom end of the stove should also be sticking out a slight amount but be crimped in such a way there is only a small orifice remaining. Placement of tube varied by engine and carburetor. Here is what one looked like in a later engine.



In operation, a length of 1/4" steel or copper tubing would have a snug push fit into the upper end of the tube. The other end of the tubing is connected to the automatic choke enclosure on the carb. When the engine starts, because of the orifice in the heat tube air flow is restricted so vacuum can only draw a small amount of air heated by the exhaust gasses up thru the tube. The heated air acts on a bimetal spring inside the choke housing. As the heat causes the bimetal spring tension to change it allows the choke to open when the engine reaches the temperature point where the choke is adjusted.

Nice_thank you

So basically, a tube comes out of the manifold and threads into the carburetor, choke

That’s great

just yesterday I was looking at my carburetor and seen a compression fitting on the choke and was wondering what it’s for


…..Hopefully someone will respond that as remade one……


I hope you make an Amazing day out of it

As long as you can figure out how to attach it you can just make one with a tubing bender. Nothing too special.

It’s actually bimetal which is something composed of two metals (bi means two) layered together rather than blended as they are in an alloy. Bimetal springs such as those used in a choke when heated will bend which, in this case, opens the choke. When the engine cools down, the choke closes again. This is probably an oversimplification but it should get the idea across!