timecapsule Posted January 28, 2023 Share Posted January 28, 2023 I have a couple questions about the Marvel carburetor heat control system on my 1930 straight 8 flathead. I've just finished rebuilding the carburetor and as I was installing it, I noticed a hole on the side of the heat control sleeve between the carb and the manifold. Upon further investigation it turned out to be the same thing as a frost plug. I poked a screw driver in the rotted through opening and give it a bit of a twist and it popped out. (3/4" dia.) The one on the other side also had a small hole in it and it too popped out. So my question is why are they there? As you may know the cast iron section has an inner wall surrounded by a cavity. That cavity collects exhaust fumes and warms up that chamber for the gas to atomize efficiently. But what I don't understand is what the purpose of the frost plugs are. I'm guessing maybe it's for access to the inside area. After I pulled them out I saw a lot of flaked cast iron and I spent about an hour pulling out bits and pieces out of there. So maybe the flaking is normal due to the heat in there and as a service procedure you're supposed to pull the plugs out every so many hours/miles, clean it out, and then put in new plugs. ?? The blue arrow shows where the plug was removed. The other pictures are of a spare part that I have that shows how it looks inside. My second question is. Does anyone happen to know the exact length of the linkage between the flap valve in the manifold to the flap valve at the bottom of the heat sleeve? ( red arrow) I'm missing that linkage and I'll have to fabricate one. Push come to shove. I'll just try to make the length so the action of both flap valves open and close in sync. I suppose. Link to comment Share on other sites More sharing options...
Jon37 Posted January 28, 2023 Share Posted January 28, 2023 If you haven't done so already, you might post this question on the Hudson Open Forum, at https://forum.hetclub.org/ Link to comment Share on other sites More sharing options...
timecapsule Posted January 28, 2023 Author Share Posted January 28, 2023 2 minutes ago, Jon37 said: If you haven't done so already, you might post this question on the Hudson Open Forum, at https://forum.hetclub.org/ It's my understanding that that open forum is being shut down or phased out in one way or another. Besides I've always had amazing success with the amazingly knowledgeable fellas here at AACA, in the various forums. But thanks for the suggestion. Link to comment Share on other sites More sharing options...
Jon37 Posted January 29, 2023 Share Posted January 29, 2023 I think they'll upgrade that forum or move it to another of the HET websites. I doubt it will be dropped. If it should move, it will probably carry all the present discussions with it to the new location. The AACA is indeed populated with very knowledgeable people, and this is definitely an excellent place to find information. The Hudson Open Forum is filled with a large number of Hudson-specific experts who (for whatever reason) never stray far from that forum. It never hurts to seek out specialized knowledge wherever specialists congregate! 1 Link to comment Share on other sites More sharing options...
timecapsule Posted January 30, 2023 Author Share Posted January 30, 2023 In Hindsight I think I should have entered this post in AACA General Discussions forum, since it is more of a Marvel Carburetor/ Marvel heat control system topic, then a Hudson topic. Hopefully someone who has that authority will do that for me. Cheers Link to comment Share on other sites More sharing options...
Jon37 Posted January 30, 2023 Share Posted January 30, 2023 A good idea! But I wasn't aware that one was prohibited from placeing a topic in more than one forum category. Have you attempted to do this yourself and been told otherwise? Link to comment Share on other sites More sharing options...
timecapsule Posted January 30, 2023 Author Share Posted January 30, 2023 29 minutes ago, Jon37 said: A good idea! But I wasn't aware that one was prohibited from placeing a topic in more than one forum category. Have you attempted to do this yourself and been told otherwise? No, but I have had moderators move a posting of mine to a different category because they thought it was more suited there. It can't hurt to post this in General Discussion and just see what happens. Btw, fortunately I did find frost plugs that were a good fit. Link to comment Share on other sites More sharing options...
paulrhd29nz Posted January 31, 2023 Share Posted January 31, 2023 (edited) Used to close the exhaust passage and force warm air threw the pre heat chamber to warm up your fuel which is 100% useless with todays modern gas. Not needed. If you find the leaver just leave it on warm The frost plug is simply there for casting purposes and nothing else. You should join the H.E.T club and get our WTN magazine. There are people in the advertising forsale part of the magazine that sell only 1930 and 31 hudson parts. Looks like a very easy part to make. ps. Post pics of your car !! Edited January 31, 2023 by paulrhd29nz Poor education (see edit history) Link to comment Share on other sites More sharing options...
timecapsule Posted January 31, 2023 Author Share Posted January 31, 2023 33 minutes ago, paulrhd29nz said: Used to close the exhaust passage and force warm air threw the pre heat chamber to warm up your fuel which is 100% useless with todays modern gas. Not needed. If you find the leaver just leave it on warm The frost plug is simply there for casting purposes and nothing else. You should join the H.E.T club and get our WTN magazine. There are people in the advertising forsale part of the magazine that sell only 1930 and 31 hudson parts. Looks like a very easy part to make. ps. Post pics of your car !! Good to know, thanks. I was scratching my head about "why" that heat diversion valve (so to say)was even there and why it was coordinated with the throttle plate. The manual say it's purpose is to optimize and better atomize the fuel/air mixture, but that's about all. I thought maybe it had something to do with the carb being an updraft style. I'll just forget about the linkage and set it as you mentioned and leave it at warm. Problem solved thanks, and as I mentioned in my last comment I found a pair of 3/4" frost plugs at napa that will do just fine. Cheers Link to comment Share on other sites More sharing options...
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