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By jumpstart - 7 Years Ago
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Good afternoon; My Question of the day is. How much of an over bore to be safe from over heating of a 57 312 block.
My block is .030 over now, But needs to be cleaned up with an over bore, Hopefully it will clean up at .050. I live in a HOT area. in the summer. Any help will be Great Bob
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By charliemccraney - 7 Years Ago
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An overbore has nothing to do with it overheating. Sonic check the walls to make sure that the walls are thick enough to go to .050.
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By NoShortcuts - 7 Years Ago
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Jumpstart. I have high regard for Charlie and the information that he shares with us on this Forum.
I also have high regard for information shared by Don Hyde. Don lives in Texas and is also very y-block knowledgeable. Don's recommendation shared with Felix Natoli when he was having a previously over-bored 312 again rebuilt was to not go over .040 overbore on a 312 to be used in the Southwestern part of the country. Don's reason for limiting overbore on the 312s is to avoid engine overheating tendencies in his area of the country particularly on Thunderbirds. Some of us believe that T-'Birds are more prone to overheating because of the 1 inch spacer Ford used between the timing chain cover and the water pump. The spacer was used o the 'Birds because Ford had a fit-up issue with pulley alignment, the generator, the 'Bird crankshaft damper, and Lord knows what else that I'm not aware of.
Charlie's point regarding the value of sonic testing the block has much merit, also. It is very common for the sand cores placed inside the sand mold used in the engine block casting process to shift slightly as the iron is poured into the mold and flows around the sand cores during the pouring and mold filling process. When the cores shift (move), the result can be that a cylinder wall's thickness may end up being more thin in one particular area after the bore was machined at the factory. Over-boring the cylinder for rebuilding purposes can exacerbate the wall thickness problem. When core shift is discovered prior to re-boring, it is sometimes workable for the machine shop performing the work to adjust the bore location slightly and compensate for the slight misalignment of the cylinder wall thereby equalizing the thickness of the cylinder bore wall.
Back to your inquiry. FoMoCo only supplied oversize pistons up to .040 over (3.840) for the '56-'60 y-block 312s. Aftermarket piston suppliers (examples: Sealed Power, Silv-O-Lite) still offer .020, .030, .040, and .060 oversize for the y-block 312s.
Depending upon the ridge at the top of your cylinder bores and the taper in your existing cylinders, you may only have to have the cylinders honed .010 oversize for 3.840 pistons.
Something else to consider in rebuilding your 60 year old engine block . . . Many machine shops have moved to hot water spray cleaning systems or oven baking of engine blocks and heads followed by the use of steel shot blasting systems to remove scale and corrosion before commencing rebuilding procedures. While the hot water washing systems, thermal baking, and shot blasting systems work well for exposed surfaces, water jackets in the engine blocks and heads can resist these cleaning techniques.
Talk to your machine shop, but consider turning to an over-the-road truck radiator repair shop to find hot soaking tanks that use an alkaline solution to remove metal corrosion and cooling system deposits in the engine block and cylinder heads. This method, using lye at an earlier time, was The-Way to have engine blocks and cylinder heads thoroughly cleaned to prevent cooling system overheating problems.
My suggestion would be to thoroughly de-grease the exterior and interior of the block and heads before talking to the owner or operator of the radiator shop. Remember to remove all engine block oil galley plugs and the oil filter adapter before cleaning. If the engine parts aren't completely de-greased before you present them to the radiator shop, they will likely refuse the work because the grease and dirt will contaminate their cleaning operation. After soaking, when the iron parts are removed from the hot tank alkaline solution and washed off with water, they will oxidize immediately. I supply the radiator shop with an aerosol can of GibbsBrand lubricant when I leave the engine parts to be soaked. I ask them to spray all of the exposed metal surfaces of the engine block and cylinder heads to prevent rusting of the surfaces before I pick them up.
Hope this helps! 
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By famdoc3 - 7 Years Ago
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I have a 57Tbird 312 which was rebuilt for the 4 th time 3 years ago. Egge had 80 over Pistons available for the rebuild. Sonic testing was good, so we proceeded with the build. Runs great, doesn't overheat on the hottest days her (hi 90's). I did do a radiator rebuild a number of years ago with a special core which had dimpled tubes and additional roes so that a 3 core radiator had the same number of roes as a 4 core. BEST move I ever made in 45 years of Tbird ownership. Good luck! MIKE
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By newbill - 7 Years Ago
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I doubt that overboring would lead to overheating, but overboring does slightly increase the displacement, the compression ratio, and therefore the horsepower output at full throttle which would add more heat load to the radiator. But it probably wouldn't be enough to cause overheating on a hot day.
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By jumpstart - 7 Years Ago
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Hello again; I do want to thank all for the help, on this. I will have the block sonic tested.And then go from there.
I am in Northern California and with the high temps here in the summer. I am concerned about over heating in the summer. Again Thank You to all. Bob
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By Y block Billy - 7 Years Ago
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over boring can lead to overheating issues, thinner walls there is less material to dissipate heat between water and cylinder temps, thus heating up water quicker. Not only that but thinner walls will expand and contract more where when hot may lead to piston slap and this heating cooling cycle on thinner walls will lead to premature cylinder distortion requiring the next rebuild to come a lot sooner than expected. always best to have as thick a wall as possible. IMHO
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