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Good Morning,
I removed my intake and exhaust manifolds to find what looks to be some type of butterfly valve between them with a linkage on the outside of the exhaust manifold but the butterfly valve has been removed... Can someone tell me what its function is and how important for me to replace it? I am attaching a photo for reference...
Thanks,

that would be the heat riser. the plate directs hot exhaust gasses to the intake at warm up to help atomize the fuel and help the carb from icing over.

the importance of the valve will be dependent on were you live and at what temp you operate the truck.

living north of the 49th I would have the valve operational. I would get a kit no matter what because the bushings the rod rides in get worn and creates an exhaust leak that will scorch the back of your hand when doing a running valve adjustment.

note : the canadian t249 251 has an automatic heat riser with a weight and a spring that controls the valve based on exhaust temp.

If you're unfamiliar with exhaust heat risers and their function, this article might be worth reading: https://www.ncrsmac.org/ed/Engine/Exhau ... ser%20.pdf

Thanks gentlemen, you guys are awesome! I live in the southern half of Texas so it won't be so important. May as well fix it while I'm this far into it...
Thanks again!

John at Midwest Military has/had the heat riser kits when I got one a couple of years ago.
Gary

Cal_Gary wrote:John at Midwest Military has/had the heat riser kits when I got one a couple of years ago.
Gary

Here's the link: https://store.midwestmilitary.com/product-p/614976k.htm

If I remember correctly, these kits require that the vane has to be spot welded to the shaft once the shaft is inserted through the bushings in the manifold casting.

I live in the Sonoran Desert. I made a brass block off plate to go between the manifolds.