piston deck height

[GMR5]

Doing preassembly on 383 street motor. New Scat crank, Scat 6" rods, KB forged pistons (1.13 comp height). Block is zero decked so my pistons should be .005 above the deck (9.005). But they are above deck these amounts: 1 .007 3 .009 5 .017 7 .015 2 .021 4 .015 6 .019 8 .012 Assuming the problem is the deck, can you give me any suggestions on the best way to proceed. I'm thinking: . just build it with a head gasket of say .060 . use 5.7 rod and a piston with a compression height which would yield 8.990 bringing the pistons down .015 . have the block decked again to 8.990? . something better anyone can suggest

[BLOCKMAN]

Originally Posted by GMR5

Doing preassembly on 383 street motor. New Scat crank, Scat 6" rods, KB forged pistons (1.13 comp height). Block is zero decked so my pistons should be .005 above the deck (9.005). But they are above deck these amounts:
1 .007
3 .009
5 .017
7 .015
2 .021
4 .015
6 .019
8 .012

Assuming the problem is the deck, can you give me any suggestions on the best way to proceed. I'm thinking:
. just build it with a head gasket of say .060
. use 5.7 rod and a piston with a compression height which would yield 8.990 bringing the pistons down .015
. have the block decked again to 8.990?
. something better anyone can suggest

With that set up your zero deck is 9.005 and with some of the cranks out there if you have the tools to check the stroke of the crank that may be a problem there and on most rods and pistons there is a plus .001 minus .001 which from low to high is .002

Are you dealing with a performance machine shop that does percise work or a local jobber shop that does not have the proper equipment to square and deck a block but to go off from what is there.

Hopefully the decks are square front to rear so aleast the bores are square to the main line.

On most blocks we machine we shoot for zero deck and on the high end rotators they seem to be pretty close and on the cheaper assemblys that are some times off up to .003 from the top of the deck.

[CFI-EFI]

Originally Posted by GMR5

Block is zero decked so my pistons should be .005 above the deck (9.005).

Zero decking means to deck the block to where the piston deck clearance is zero. Not to where the pistons should be .005" above the deck. Based on what you've written it is hard to guess what your block is decked to. The blueprint dimension of the block is 9.025". Based on your dimensions, it is impossible to tell where the problem is, but more than likely it is in more than one place. Even if the crank doesn't have uniform strokes on all the journals, the #1 and #2, which share a journal, should have similar deck heights. They are different by .014" with the left side of the block being the highest. My first thought was that the block wasn't decked the same from bank to bank. But then I looked at the rear crank journal and the #7 deck is .003" lower than the right bank, the opposite direction of the front journal. You should do some careful checking of the block, the rod lengths, compression height of the pistons, and yes, the crank stroke too. Possibly by mixing and matching parts you can come up with acceptably uniform deck heights, but it is doubtful. A super thick head gasket would just be a band aid and negate the purpose of decking the block in the first place. You have some serious dimension checking (measuring) to do.

RACE ON!!!

[GMR5]

thanks for your replies