Thee Antic

iTrader: (1)

Alright so first off, this was supposed to be a zero deck. My retarded local machine shop said **** me and ignored the measurements I gave them to bring it to zero deck apparently.

During mock up the pistons ranged from 0.007-.008 in the hole. Now they are as follows.

#1 - 0.012 inner, 0.017 outer, 0.007 center

#2 - 0.016 inner, 0.009 outer, 0.006 center

#7 - 0.014 inner, 0.020 outer, 0.008 center

#8 - 0.015 inner, 0.009 outer, 0.006 center

Piston bore clearance - .0038 - .004

So now how do I translate that into numbers I can use for determining proper quench and compression? Thanks guys

RezinTexas

So now you are 6-8 thou out of the hole? This is a good number, you could run a 45 thou gasket for 38ish quench.

Thee Antic

iTrader: (1)

I should clarify, I measured the piston's edges at their highest points. So when measuring the inner side I pushed down on the outer and vice versa.

After a little more research it looks like the center number is the number I'm looking for since that's the number with no rock interference. Am I right?

KCS

iTrader: (20)

The best way to measure (at least in my opinion) is to put the tip of the indicator at the edge of the piston and rock it. Measure the value at its highest and lowest, then add them and divide by two. That number either added to the low or subtracted from the high will give you your distance above or below the deck.

Example A:
High = + .017" (above the deck)
Low = -.001" (below the deck)

.017" + .001" = .018" (total distance rocked)
.018" / 2 = .009"
.001" + .009" or .017" -.009" = .008" out of the hole

Example B:
High = + .017" (above the deck)
Low = + .001" (above the deck)

.017" - .001" = .016" (total distance rocked)
.016" / 2 = .008"
.008" + .001" or .017" - .008" = .009" out of the hole

Thee Antic

iTrader: (1)

Which side of the piston should I do that for? Inner or outer?

KCS

iTrader: (20)

Both. That will tell you how square the deck is too.

Thee Antic

iTrader: (1)

After crunching the numbers this is what I got.

__________Outer________________Inner
#1 .019 & .003 = .011___.014 & -.003 = .0055

#2 .011 & -.005 = .003___.017 & 0 = .0085

#7 .021 & .003 = .012___.015 & -.002 = .0065

#8 .010 & -.003 = .0035__.015 & .001 = .008

Now do I need to average these or do I use a particular side? How do I get a solid number to use for calculating compression?

KCS

iTrader: (20)

On the #1 cylinder, are the "outer" measurements both above the deck?

Thee Antic

iTrader: (1)

Yes, -.00x represents in the hole.

Did I mess it up?

KCS

iTrader: (20)

No you got it. Those numbers are all over the place though, geez!

Thee Antic

iTrader: (1)

Yeah the initial shop I had do my work fucked everything up.

The bore size's were all off, tapered etc. When they ported the heads they gouged the valve seats and a ton of other mishaps. You name it, they messed it up.

So how bad are those numbers? Should I do anything about it?

And my first question still stands, how do I get a solid number for compression calc's?

KCS

iTrader: (20)

It's fixable at least. A good shop can get the deck closer to square with the numbers you have and you could still run a GM MLS gasket if you wanted. If it were me, I'd have it fixed, at least get the left and right banks closer to matching.

For each bore or bank, I'd just use an average between the outer and inner.

Thee Antic

iTrader: (1)

Right. Well I just had the short block fully assembled by the guy who fixed all of the machine work..is it really worth paying to tear it back down? It is a DD afterall. Is this going to lead to premature failure or what am I looking at here?

The driver side bank averages out to .00875 and the passenger side bank averages to .00575.

I'm around 11.5:1 compression so I want to keep my quench in check, I was thinking .045 cometic's if I leave the deck as is. For a quench of .0362 on the driver side and .0392 on the passenger side. But that might be a little tight on the driver side. I have 3.2cc valve reliefs and a medium cam so I don't see PTV clearance being an issue.

What are your thoughts? I'm still learning and making this call seems to be above my paygrade.

Thee Antic

iTrader: (1)

My machinist is saying the initial shop probably just decked off the stock deck which usually has a .005-.007 variation. He doesn't know why they took so much material off though.

He says he would have paralleled it to the crank but he would have had to mill my pistons to make up for taking so much material off of the deck. He was trying to save me cash.

He says to run it since it's a DD, I would like some additional opinions though.

KCS

iTrader: (20)

.036" is too close for me, I'd run a GM MLS gasket. They're cheaper and safer.

On the other hand, I don't see why you couldn't run one on either side to balance the two banks out. Kinda ghetto fab, but it would work.

Thee Antic

iTrader: (1)

Are you trying to say run different sized head gaskets to make up for the difference in deck height? I was just thinking that myself.

As much as I would like to run the GM MLS .054, it puts my quench too high.

If I run a .049 cometic on the driver side and .046 on the passenger side I'll be spot on .040 quench and 11.27 static compression for both sides.

As-is the difference would boost the driver side compression by .08. Enough to care about I think.

So you think the head gasket band aid would work?

Russ K

iTrader: (1)

.035-.040 squish clearance is a common target on an aluminum block LS engine. As the deck height increases at operating temp.

Russ Kemp

Thee Antic

iTrader: (1)

Yes thank you, I have read that before.

We were talking about running different size gaskets to make up for the .003 difference from the driver side cylinder bank to the passenger side.

KCS

iTrader: (20)

Yeah, it should work just fine. It's not really a big difference so it may not even affect pushrod length, unless you're using short travel lifters.

Thee Antic

iTrader: (1)

Alright so I've found a problem with my theory. Cometic's "any thickness, any bore" policy is only if you want to choose from there pre-selected thicknesses. I understand since it probably wouldn't be a financially sound decision to make one off gasket sizes for every customer that ran into an odd situation like this.

So here's my new plan.

.054 GM MLS on the driver side and .051 Cometic on the passenger side.

That still makes up for the .003 difference while keeping my quench at an "OK" .0455. At least one of my heads will have the safety of a GM MLS now hahaha