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deck height ? on 427
Looking at a 427 s/o short block, the block was decked and now the pistons come .030 above the deck, i will be putting Edlebrock heads on this motor with 72cc , any help would be great Bob
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Something isn't right, you shouldn't have any piston above the deck, it sounds like a combination for some piston and head interference. The block has obviously been decked,but that seems extreme. If all checks out on disassembly, I would have the pistons cut. The factory clearance is .018,since it is older and you'd expect some machine work has been done,it would be a little tighter. I don't think you could find a gasket thick enough to negate that much protrusion above the deck. If you're looking at buying it, I might be a little leary, if you already own it you need to figure out why the slugs come up so high.
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What crank and pistons are in it?
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Good question FFR
There are several combinations that will cause this as well as a deck height issue. It boils down to wrist pin location for the different stroke/piston combinations. IF you can, get the number off a piston and check it with the manufacturer to see what it is supposed to fit. A little unlikely but not impossible, is that someone had the crank ground with an offset to use smaller rod journals and or change the stroke and the pistons are not the problem at all. If you can, accurately, check the stroke with a dial indicator and/or a precision caliper (they have a depth rod). It should be 3.73" (less deck material removal and bearing clearance) from deck to piston top at bottom dead center. Hope this helps. Al |
Something is out of whack...
You will need to determine the true deck height of the block.
The stock deck height of a 427 is 10.17" If the crank, rods and pistons are correct then that means your block has been cut .040" to .050". If you care to use a block cut that much custom pistons will be required. You will alsohave tons of fun getting the intake manifold to fit and of course custom pushrods will be required. I hope your block is not cut that much and you will just need new (correct) pistons --Mike |
Deck clearance specs are 0.0005, 0.005 or 0.018 inch depending on the pistons used. Sounds like you'll have to flycut your pistons to achieve the needed deck clearance, or 0.0005 inch minimum. Also, check valve-to-piston clearance to make sure the valves and pistons don't collide.:(
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I have a friend who uses copper shim gaskets to get the desired deck height,,he says the seal is better too,either way,if the short block is a good buy,you can fix it,if not steer clear and wait for a better deal.
the true nascar blocks were milled .050. before they left ford,this was to get the compression up with changing rods/pistons Tim |
I t seems like the block may have been decked more than 1 time or decked a bit much. eather way deck height is the amount of clearance between the top of the piston @TDC & the deck of the cylinder head. This is usually .035- .040 with steel rods. This includes the head gasket. Example, piston @ .000 deck, gasket @ .039 thickness (Fel-Pro type), would give you a deck height of .039. In times past Ford would run the piston @-.018 down the hole with about a .022 thick shim type head gasket giving a total of .040, Simple!
Hope this helps, Mike |
Mike: I believe what you describe is piston-to-cylinder head clearance. Actual deck height is the distance the top of the flat surface of the piston is from the top of the cylinder-block deck with the piston at top dead center. The minimum for this on a 427 is 0.0005 inch, but 0.018 inch will surely work. Whatever deck height is, you've got to ensure there will be no piston contact with the cylinder head.
Check out how to determine deck height by clicking on: http://www.2strokeheads.com/Deck_Height.html |
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