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 Blocks / Cranks/ Rods and Pistons
 decking a block
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dannygote
Tribal Scout

USA
1 Posts

Posted - 09 Mar 2020 :  2:19:56 PM  Show Profile  Reply with Quote
NOT SURE IF THE FIRST TIME I TRYED TO POST WENT THROUGH SO HERE IT GO'S AGAIN ==== hi ..I haven't been on in a while but I have ?? for some one who knows how much to deck the block to get 0 deck height on a 40 over 428 ..the pistons I am buying have a 1.5938 pin height .. I have done the math { the way I understand it } .0312 on the deck height is what I came up with but I need to know how much to deck the block is it .0312 ? are these figures correct ?? I really am trying to keep from possibly making a costly mistake

Danny Williamson

Steve C.
Chief PONTIAC

2141 Posts

Posted - 09 Mar 2020 :  3:03:36 PM  Show Profile  Reply with Quote
It is often necessary to remove some material from the block just to "square up" the cylinder heads. The deck of the block must be perpendicular to the crankshaft centerline. In a V-8, the decks on both sides of the block are at 90-degree angles to each other. A block should also be decked to ensure a good, flat surface so that you can achieve a good gasket seal. It is not always a set amount.
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Corncob2061
Crazy Horse

USA
669 Posts

Posted - 09 Mar 2020 :  6:36:13 PM  Show Profile  Reply with Quote
This varies for each block... The measured height number is also too specific of a number. No one can machine something to the ten thousandths of an inch (.0001). One thousandths of an inch is as close as most machine shop equipment come (.001 +\-.0005). Assuming 10.24 deck height and 1.594 compression height, 6.625 rods and 2 inch stroke it takes .020 cut to zero deck. Most Pontiac deck heights run between 10.23-10.25.

Edited by - Corncob2061 on 09 Mar 2020 6:37:13 PM
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Steve C.
Chief PONTIAC

2141 Posts

Posted - 09 Mar 2020 :  6:45:23 PM  Show Profile  Reply with Quote
Dick Duclow from the old Indian Adventures stated his factory blueprints on hand suggested 10.2437". However I've seen it stated from 10.225" to 10.235", but more often than not 10.230" is used.

That said, it was also stated the blueprint in question would specify the minimum height allowed by the casting house with the ability by Pontiac to machine to the 10.230" dimension prior to assembly. If it was less than that the QC inspector would reject the block castings.

I had one build where it ended up at about 10.215" to get it square.

Edited by - Steve C. on 09 Mar 2020 6:48:39 PM
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DanM
Cochise

238 Posts

Posted - 14 Apr 2020 :  3:21:29 PM  Show Profile  Reply with Quote
You won't know how much to remove until you have installed the rotating assembly. Then you measure it as is. Then you remove the rotating assembly and machine the deck.
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DanM
Cochise

238 Posts

Posted - 14 Apr 2020 :  3:29:55 PM  Show Profile  Reply with Quote
...80,000 miles ago I had my block machined to 0 deck height. If I remember correctly it needed about 0.015" taken off but it was not square so it took more on one end then the other.

This time we remeasured the block after disassembly. We took into account the minimum that can be taken off - 0.007" - to provide a fresh surface then used that new deck height to specify the compression height of the pistons in order to get them back to zero deck height. These pistons required a support ring for the lower oil ring because the compression height was so low.

After final assembly we confirmed the pistons were all 0.008" in the hole. Then we used that measured value to specify the chamber volume (92.5 cc) for Dave Bisschop to do his final cut on the heads. Goal is 9.5:1 compression.
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DanM
Cochise

238 Posts

Posted - 14 Apr 2020 :  3:35:25 PM  Show Profile  Reply with Quote
You could do all this in advance and probably get pretty close. I did it that way last time and it worked fine for many years. This time I was ordering all new custom parts anyway so I did it in steps. Also since the heads took 4 months I had plenty of time to do the bottom end before completing the heads.

Now I have the problem of not knowing what length pushrods to use. So, we will assemble it, measure it, order them, then install them.

Taking forrreeeeevvvveeeerrrrrrrrr

71 LeMans Sport Convertible with 350,000 miles driven year round since 1994.
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