Block decking ?
Team Owner
Joined: Apr 1999
Posts: 21,953
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From: Reno Nevada
2024 C3 of the Year Finalist- Modified
Re: Block decking ? (DVG73)
I would only true it up for a better gasket seal. True zero decked blocks are a pain in the butt because you have to worry about piston selection for head quench gap. You want to keep the quench right around .040 You get this figure from the amount the piston is down from the deck at top dead center plus the gasket thickness after it is torqued down.
Le Mans Master
Joined: Mar 1999
Posts: 6,744
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From: delmont pa
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Re: Block decking ? (DVG73)
unless you are using a aftermarket pistons,rods and crank the stackup tolerance on stock GM stuff could cause you trouble with the deck height. i have seen as much as .008 difference in deck heigth on the same engine. :chevy
Thread Starter
Racer
Joined: Sep 2000
Posts: 485
Likes: 1
From: Dallas Texas
Re: Block decking ? (clem zahrobsky)
Clem,
If I understand you right , you are saying that decking the block can lead to clearance problems with GM stuff, I plan on using the crank and reconditioning the rods but using aftermarket pistons. It sounds like I am better off not doing it.
Thanks for the info.
If I understand you right , you are saying that decking the block can lead to clearance problems with GM stuff, I plan on using the crank and reconditioning the rods but using aftermarket pistons. It sounds like I am better off not doing it.
Thanks for the info.
Le Mans Master
Joined: Mar 1999
Posts: 6,744
Likes: 1
From: delmont pa
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Re: Block decking ? (DVG73)
if you want to deck the block you will have to trial fit the crank,rods and the new pistons in all the clys,check each one at DTC and go from there to see what deck distance you have before you deck the block. :chevy
[Modified by clem zahrobsky, 12:46 AM 6/4/2002]
[Modified by clem zahrobsky, 12:46 AM 6/4/2002]
Race Director
Joined: Nov 2000
Posts: 11,872
Likes: 12
From: Waterloo ontario Canada
Re: Block decking ? (DVG73)
For my personal engines I do deck the blocks. It does involve assembly and carefully measuring how much must come off. My last engine needed .030 from one side and .032 from the other. I feel it wakes the engine up a little if you are willing to do the work.
Instructor
Joined: Jun 2001
Posts: 231
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From: Cedar City UT
Re: Block decking ? (norvalwilhelm)
Besides trueing up the block for sealing ,the second reason for zero decking a block is to control detonation. An engine with 9.5/1 C/R and .070 cylinder quinch will detonate more readily than an engine with 10/1 C/R and .040 cylinder quinch.
You don't have to take the block to zero deck either. You can have the same effect by using .020 steel shim Head Gaskets on cylinders with a .020 depth and leave material for another rebuild. The effective cylinder quinch is .036 to .050 with .040 being perfect.
If your using reconditioned rods you'll want to chk the piston depth in the cylnder using a dial indicator for top dead center and a depth gage to take the measurements at the center of the piston. Don't be surprised to find up to .010 difference in measurements in using reconditioned rods. If you take measurements at the front and back of the piston at TDC you can chk your rod to piston alignment which won't show up when they chk the rods alone in their jig.
All of this means you'll be taking this engine and mocking it at least once without rings to chk what you have or you'll be taking chances with machine shop geting it right which I would'nt do unless their doing the complete rebuild.
LOL BOB
You don't have to take the block to zero deck either. You can have the same effect by using .020 steel shim Head Gaskets on cylinders with a .020 depth and leave material for another rebuild. The effective cylinder quinch is .036 to .050 with .040 being perfect.
If your using reconditioned rods you'll want to chk the piston depth in the cylnder using a dial indicator for top dead center and a depth gage to take the measurements at the center of the piston. Don't be surprised to find up to .010 difference in measurements in using reconditioned rods. If you take measurements at the front and back of the piston at TDC you can chk your rod to piston alignment which won't show up when they chk the rods alone in their jig.
All of this means you'll be taking this engine and mocking it at least once without rings to chk what you have or you'll be taking chances with machine shop geting it right which I would'nt do unless their doing the complete rebuild.
LOL BOB
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Instructor
Joined: Sep 2001
Posts: 171
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Re: Block decking ? (DVG73)
Does the block need decking? I feel your ? should be, do I need to check it? You wont know if it needs decking till you check what you have. This should be done B4 you choose your replacement parts. This also should be done B4 the block finds it's way to the machine shop. A block that needs to go back and forth to the machine shop shows poor planning. What will the engine be used for? How critical do you want do be? With a little thot, you can stabilize one original piston assembly wo/rings in the four corners of the block to show you exactly where you stand. A straight edge with feeler gauges will show how flat it is, if that is all you are interested in. If you are putting in a different combination of parts, you need dimension comparisons to determine if any material needs to come off the block, regardless of how square it is, to get the deck hgt./quench hgt. you are trying to achieve. BTW, engine (dis)assembly is more than ripping parts off. Checking can be helpful as the engine is taken apart. There is a reason why (true) 'blueprinting' is more costly. Happy engine building!
Melting Slicks
Joined: Apr 2002
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From: down that one road next to that big tree
Re: Block decking ? (68shark)
i decked mine to zero, it's not hard to make up for, + since you have to buy new pistons anyway what's the problem? great way to tighten up quench
