[ponchjoe]

Is there a norm or average when zero decking? I bought a machined block and the seller couldn't find the receipt but thought .017 was removed (sounds like a lot to me) So what's average and what's too far?
Here's the spec on my Pistons..

Thanks
Joe

[PAUL K]

No problem with .017. I don't think there is an average, but when using the old TRW 400 powerforged pistons it takes around .025 to get them to zero deck.

[71firebird400]

I'd have to check my notes but I believe my 400 block was decked about .014" to achieve zero with Ross pistons and an Eagle 4.25" crankshaft.

[DeanBenson]

I had my 400 decked this week, stock crank and rods, TRW 2262 pistons, took .015 on left bank, took .022 front and .027 rear off right bank to get all pistons to zero. From what I've read, the OEM deck heights vary front to back and side to side.

[GRX]

Ahhh ... engine blueprinting. Seems to me such variances can be attributed to quality control at the factory. It would be nice if a machinist calibrated the equipment for each individual block. But that would be too time consuming & expensive when doing large production numbers. This is why no one single number can be tied down since no two are exactly alike.

[hurryinhoosier62]

Originally Posted by GRX

Ahhh ... engine blueprinting. Seems to me such variances can be attributed to quality control at the factory. It would be nice if a machinist calibrated the equipment for each individual block. But that would be too time consuming & expensive when doing large production numbers. This is why no one single number can be tied down since no two are exactly alike.

Dittos. There is NO "norm". Since every block/crankshaft/piston/connection rod has variances in the casting/forging/machining processes, there isn't one set amount of material to remove. I have two '72 400 blocks under my workbench. One has a block height of 10.240 inches (std height). The other is 10.245 inches. BOTH are virgin block. Likewise, I've seen pistons with .002-.005 variance in compression heights in the same set; connection rods with .003-.005 variance in rod c-to-c length in the same set. Let's not get started on crankshafts. I've seen them as much as .020 out of stroke from the factory. To realistically zero deck a block, you first have to measure all the components and establish what the zero deck height should be. Then, machine the block accordingly.

[cdrookie]

i had .030 removed from mine and the pistons still sit .005 in the hole. JE pistons/eagle rods/stock crank.

[gtofreek]

I've seen factory block decks range anywhere from 10.220"-10.250". Earlier blocks are taller. I've had to take .015" off some blocks just to get one deck cleaned up, and the twist taken out of it. We have to keep in mind that production engines are done on an assembly line in jigs, that work off of the oil pan rail, not the main housing bore. We deck blocks off of the main housing bore to get both decks square to each other, and the mains. On production blocks it is not uncommon to get a metal chip or a burr that prevents the block from sitting square in the jigs. This can result in twisted decks, height differences from front to rear, and side to side. Production blocks are far from perfect[contrary to some popular belief], and Pontiac's are no exception. Some of the worst decks I have seen where on Pontiac blocks.

So, yeah, there is no norm.

[74Grandville]

maybe i shouldn't have cut so much, but i did .035 on mine to zero. one deck was funny in the rear. cast speed pro's used.

[Cliff R]

I've seen blocks off as far as .027" from one bank to the other, and nearly that much in taper from front to rear.

I've also had 455 blocks in here fitted with TRW forged pistons (taller than stock pistons) that were almost EXACLTLY zero decked across both banks and needed nothing machined from them at all.

The rule of thumb for cutting heads and blocks is around .060". At or close to that point we start running into a situation where the intake will not sit down far enough to line up the bolt holes. You can elongate the holes or do one even better and have either the intake face of the heads cut, or the bottom of the intake.

It's also best to try to come up with a piston/rod length that puts the pistons no more than about .020" in the holes at TDC. This gives the machinist enough room to work with to get you to zero deck on both sides.

We consider decking/squaring and establishing tight quench MANDITORY for these engines at any power level. Your engine will reward you in several ways.

It will take LESS timing to make optimum power, and less octane to make that power. Most of these engines will also run cooler as they have improved combustion efficiency and naturally turn more of the heat into power rather than transmitting it to the jacket water.

The engine will also be more "balanced", as it's going to be closer in compression every cylinder assuming the combustion chambers are pretty close to the same size.

When it comes to this topic, and making optimum power with a street/strip engine on pump fuel, it's one of the places the engine builder needs to spend funds to end up with a better overall end result.

If you go after your new engine build doing this in every area, like good valve/seat work, effective head porting, cam selection/ putting it in the right place, full control of spark/fuel curves, etc, then you are going to enjoy that engine more than one that you grabbed up a set of 8 valve relief std bore pistons for, honed it with a rock, tossed in some rings, and put poorly chosen cam in it without degreeing and placed it in service......IMHO......Cliff

[74Grandville]

Originally Posted by 74Grandville

maybe i shouldn't have cut so much, but i did .035 on mine to zero. one deck was funny in the rear. cast speed pro's used.

let me correct my statement. i don't know of they were speed pro's, no named cast 455 pistons

[Half-Inch Stud]

0.015 on my best engine assy; someone else owns it now.

think my present running engine (&spare engine) are Factory uncut decks & the slugs were custom for flush or slightly (.005) out.

[gtofreek]

Originally Posted by 74Grandville

let me correct my statement. i don't know of they were speed pro's, no named cast 455 pistons

If they have an "S" cast into the pin boss, next to the piston pin hole, they are made by Sterling[they make the cast pistons for Sealed Power], who makes a damn good cast piston. No worries there.

[GRX]

Experienced all the above when blueprinting my 400. Decks on the virgin ra3 block were not square with the main center line, NOS factory rods were not consistent center to center, and most of all, I had to grind the crank rod journals 0.030 under to get them all indexed right. In my eyes it is inconsistencies like this which make one factory assembled engine run well, and another really perform. Also machined a lot of mopar engines back in the day and when talking 60's era muscle, it seemed to me they were the worst in regard to quality control.

[72LuxuryLeMansLa.]

With the 6.625" rods, Racetec pistons with a 1.575" compression height and a 4" stroke crank I believe my machinist had to remove .040" to achieve a zero deck height from a virgin 400 block.

Your deck height would have to be 10.220" with a 4.21" stroke and 6.625" rods with the pistons you have. Do you have 6.625" rods? What stroke is your crank?

[Stan Weiss]

Originally Posted by ponchjoe

Is there a norm or average when zero decking? I bought a machined block and the seller couldn't find the receipt but thought .017 was removed (sounds like a lot to me) So what's average and what's too far?
Here's the spec on my Pistons..

Thanks
Joe

Joe,
Based on the picture you posted it should take 0.025" to zero deck. 4.21" stroke, 6.63" rod, 1.490" CH = 10.225". It says OEM Height 10.250"

10.250" - 10.225" = 0.025"

Stan

[gtofreek]

Originally Posted by Stan Weiss

Joe,
Based on the picture you posted it should take 0.025" to zero deck. 4.21" stroke, 6.63" rod, 1.490" CH = 10.225". It says OEM Height 10.250"

10.250" - 10.225" = 0.025"

Stan

OEM heights varied from 10.220"-10.25", with everything in between. No way to say how much to remove without measuring a specific block.

[rtanner]

i think my last 455 was .010 out of the hole, worked out really good,

[Stan Weiss]

Originally Posted by gtofreek

OEM heights varied from 10.220"-10.25", with everything in between. No way to say how much to remove without measuring a specific block.

Paul,
Agree.

Stan