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By ghancock - 4 Years Ago
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Heads are bad on my old 239. Block is good. I can rebuild the 239 heads; however, I have a set of 312 heads with matching 4bbl intake that will bolt on without the usual intake port matching problems. Question: will the 312 heads (identified by serial number) fit the 239ci engine? I acknowledge that the matchup w might be "putting lipstick on a pig"; however, I am in a time crunch and the question remains: Will the 312 heads work on the 239 ? Thanks!
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By Cliff - 4 Years Ago
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Some will and some won't there are 2 239 engines match up the head gasket that will let you know.
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By pintoplumber - 4 Years Ago
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What version 239 do you have? ‘54 car or ‘55 truck. If you have an early 239 the water passages won’t line up. You need to drill a water passage in the block at #4 and#8 also weld the little triangles to support the new head gasket..
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By ghancock - 4 Years Ago
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Thanks for the reply! A funny story on myself: Years ago, I stayed overnight at a motel in Letitz. When checking out in the morning, much to the amusement of the two female desk clerks, I asked where there was a good place to have breakfast in your town; however, I pronounced the name as "le Tits". They giggled and tried several times, to my discomfiture, to teach me how to say it, without success. Finally they helped me out by making me repeat the word "lettuce". Then I knew how to handle the name while I was in town and not embarrass myself further. I guess that what happens to southern boys when they wander up north!
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By Hoosier Hurricane - 4 Years Ago
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Won't the intake valves crash into a standard bore 239? Maybe the bores would have to be notched to clear the valves. Dennis, I realize your bores are no longer standard, have you ever put G heads on a standard bore block?
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By pintoplumber - 4 Years Ago
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John, I have G heads on my 239 since 2013. Standard bore 272 flat top pistons and a 312 crank.
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By Florida_Phil - 4 Years Ago
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Who wouldn't want to stay in "Le Tits"? I know I would. 
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By darrell - 4 Years Ago
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272 piston are.125 over 239.
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By pintoplumber - 4 Years Ago
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Yup, I didn’t know anything about sonic testing when we did that.
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By Hoosier Hurricane - 4 Years Ago
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G headed valves will clear the 272 bore, Ford put G heads on 272s in '57.
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By ghancock - 4 Years Ago
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Thanks!
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By Ted - 4 Years Ago
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As John points out, the ‘G’ heads were available on the 272’s and the only issue with running them on any Y engine would be when running the valve lift much higher than stock. By design, the intake valves on the Y-Block heads are positioned such that they will hit the cylinder walls thus preventing them from free dropping into the cylinders. While this has likely saved many an engine from catastrophic failure, this does limit the amount of amount of valve lift you can safely accommodate without taking appropriate corrective action.
For Y builds using oem iron heads, I use the 0.535” intake valve lift number as the maximum lift that can be used without having intake valve to cylinder wall clearance issues. Any intake valve lift values higher than that requires that the cylinders to be notched for intake valve clearance. Here’s a picture of what happens when you put too much lift where the cylinder has not been notched to accommodate it. That’s easily corrected by simply notching the cylinder walls appropriately. Just don’t notch too far down where the top ring rides in the cylinder bore.
And here’s a picture of the notch that alleviates the problem.
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