Deck Height
Le Mans Master
Joined: Oct 2005
Posts: 9,429
Likes: 44
From: Macon, GA
You'll need to assemble the bottom end. Move piston to TDC, and measure the distance between the flat top surface of the piston (not the top of a dome or the bottom of a valve relief) and the top of the cylinder. Enter a negative number if the piston's flat surface sticks up past the top of the cylinder. At TDC the piston will "rock" so be careful in your measurements.
Le Mans Master
Joined: Sep 2001
Posts: 7,739
Likes: 630
From: Unreconstructed, South Carolina
Stock sbc deck is speced at 9.025" ... that's measured from centerline of crank to top of deck. Piston height at TDC (stock varies ~ 0.045" ~ 0.025" down in hole below deck @ TDC) ... that's measured from piston crown to top of deck ... as in sperkins' pic.
If you KNOW the piston's compression height or distance, KNOW stroke, KNOW rod length and KNOW piston height in bore at TDC (aka deck clearance) ... you can calculate what the deck height is.
If you KNOW the piston's compression height or distance, KNOW stroke, KNOW rod length and KNOW piston height in bore at TDC (aka deck clearance) ... you can calculate what the deck height is.
Le Mans Master
Joined: Jan 2006
Posts: 6,504
Likes: 139
From: Butler Pa
You can calculate what it "should be". In reality, it'll probably be slightly different.
Le Mans Master
Joined: Sep 2001
Posts: 7,739
Likes: 630
From: Unreconstructed, South Carolina
Machinists routinely measure deck height of empty block. Clamp a straight, true round bar in mains between M1 & M2 ... measure plumb & square from deck to bar ... ADD 1/2 diameter of bar ... for sbc350 the MB housing bore diameters are about 2.641" ... for sbc400 they're about 2.841". Don't make any sine error and it'll be dead on the $.
-edit- ADD
Last edited by jackson; Feb 13, 2007 at 11:03 AM.
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Le Mans Master
Joined: Sep 2001
Posts: 7,739
Likes: 630
From: Unreconstructed, South Carolina
TT ...YOU can probably make one. http://www.starperf.com/tabloid/page_127.htm has deck bridge (comes without dial indicator; use yours)
magnetic P/N REN.67970 about $37
non-magnetic P/N REN.67980 about $28
magnetic P/N REN.67970 about $37
non-magnetic P/N REN.67980 about $28
Last edited by jackson; Feb 13, 2007 at 11:54 AM.
Race Director
Joined: Dec 1999
Posts: 16,945
Likes: 9
I have a home made TDC tool that i use and flip around for use w/ feeler gauge but this is a lot nicer, then again, I could also drill a hole in my present TDC tool...but then not even 40$ for a new tool 
hard to argue with that. 
hard to argue with that.
Last edited by Twin_Turbo; Feb 13, 2007 at 03:51 PM.
Thread Starter
Burning Brakes
Joined: Oct 2006
Posts: 1,089
Likes: 43
From: Native Californian CALIFORNIA
Army
Stock sbc deck is speced at 9.025" ... that's measured from centerline of crank to top of deck. Piston height at TDC (stock varies ~ 0.045" ~ 0.025" down in hole below deck @ TDC) ... that's measured from piston crown to top of deck ... as in sperkins' pic.
If you KNOW the piston's compression height or distance, KNOW stroke, KNOW rod length and KNOW piston height in bore at TDC (aka deck clearance) ... you can calculate what the deck height is.
If you KNOW the piston's compression height or distance, KNOW stroke, KNOW rod length and KNOW piston height in bore at TDC (aka deck clearance) ... you can calculate what the deck height is.
Rod length is 5.7
Stroke is 3.48
How do I get the crank throw radius for a 350? With the above information, IN THEORY, I can sum them and subtract from 9.025 and get the deck heught, correct?
Le Mans Master
Joined: Oct 2004
Posts: 5,269
Likes: 54
From: Orlando Florida
St. Jude Donor '05
1/2 stroke is 1.740"
1.740+5.700+1.561 = 9.001
If your block is not decked then the piston top (at TDC) should be .024" below the deck surface
Le Mans Master
Joined: Oct 2004
Posts: 5,269
Likes: 54
From: Orlando Florida
St. Jude Donor '05
Measure how far the pistons are below the deck, then you know what was removed from the stock deck height 9.025"
Example: Your piston is .010" in the hole means your deck height is 9.011" (that's given a 3.480" stroke, 5.700" rods and pistons with compr height of 1.561")
Racer
Joined: Dec 2006
Posts: 417
Likes: 40
From: Swansea IL
Tolerances!
Doing the math and adding up the "Listed" dimensions will give you a theoretical deck height.
What are the tolerances that the rods, crank, and pistons are manufactured to? That is the unkown. The fixtures and gauges to measure all these components to that degree don't come cheap!
Is the rod actually 5.700 or is it 5.705? The next rod is 5.710? Stock rods have a production tolerance, as do the pistons. Once all these components have been machined to a specific dimension, then you can add the numbers up and get a deck height.
That is why you actually '"Measure" each individual pistons on their respective rods to determine the actual deck height.
RGDS
Bob
What are the tolerances that the rods, crank, and pistons are manufactured to? That is the unkown. The fixtures and gauges to measure all these components to that degree don't come cheap!
Is the rod actually 5.700 or is it 5.705? The next rod is 5.710? Stock rods have a production tolerance, as do the pistons. Once all these components have been machined to a specific dimension, then you can add the numbers up and get a deck height.
That is why you actually '"Measure" each individual pistons on their respective rods to determine the actual deck height.
RGDS
Bob
Last edited by Bob3700; Feb 17, 2007 at 01:01 AM.
Drifting
Joined: Aug 2004
Posts: 1,883
Likes: 124
From: Lubbock TX
My local machine shop runs a 3-axis CNC machine. They can fasten a block in it, zero the machine (by the way, the dowel holes in the deck of big blocks are the measurement/location points), then measure it to .0001. If the block has been decked, the stamped numbers will be gone (or mere shadows of their former selves). In order to determine if yours needs to be decked, assemble the block with pistons at all 4 corners, then measure how far the pistons are down in the hole. Generally, if you're off more than about .002 - .003 on one side, you'll need to have the block decked for a performance engine.
