# Different Deck Ht on 389



## 1966gtoman (Dec 21, 2015)

I'm rebuilding a 389 where it appears the deck heights for one side of the block is different than the other. I base this assumption on the measurements I did on the assemble short block and the distance the pistons come out of the hole, yep all pistons are above the deck height. 

I'm not a professional engine rebuilder but know my way around the engine. 

I have the pistons installed and have measured each piston height above the deck height with a dial gauge. I measured everything twice to make sure I didn't have any errors so I believe the numbers below are accurate. 

I found the following (all measurements are above the deck, pistons out of the hole!):

Measurements from piston tops relative to block deck.

1 0.003
3 0.0015
5 0.0032
7 0.0020

2 0.0138
4 0.0175
6 0.0170
8 0.0180

My concern is the Quench area with one side (2,4,6,8) of the block being so much different than the other.

For instance cylinder 8 will have 0.021 clearance with a FelPro gasket while cylinder 7 will have 0.037 clearance. I've read recommendations that state 0.040 is the Quench clearance you should have.

This block was prepared by a machine shop several years ago and supposedly the block was zero decked at that time. I'm using the same pistons, rods, crank and heads so I assume this was the condition before the rebuild. I did have the block align bored for this rebuild due to some main bearing issues and the cylinders honed for new rings.

The rebuild includes new rings and bearings. The first rebuild used FelPro head gaskets which compress to 0.039 according to FelPro. No evidence of piston contacting the valves or heads. The pistons were dished during the original rebuild and the compression ratio is believed to be 9.2:1.

The car is a show/cruiser car, no drag racing. 

Should I be concerned with the Quench clearances above or just go ahead and reassemble using the stock FelPro gaskets?


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## oldskool (Apr 26, 2015)

Align boring moves the crank centerline slightly closer to the deck. But most engine builders say it's OK to run most pistons up to .005 above deck. Some guys do it on race engines just to get a little more compression.

How about switching to the Cometic 4.160 X .045 or .051 gaskets, just to be safe ?

Cometic Gaskets C5711-045, Cometic Pontiac Cylinder Head Gaskets | Cometic Gaskets

Cometic Gaskets C5711-051, Cometic Pontiac Cylinder Head Gaskets | Cometic Gaskets

I don't think the side to side difference is a big deal. But, I suppose, rather than cutting one deck down(since the pistons are already out of the hole), you could run different thickness gaskets on each side, to make the quench distance more equal. Don't think that small amount will have any adverse affects on anything.

Now if you try to run a 72cc 400 head on one side and a 114cc 455 head on the other side, now that would cause a problem, I suspect.


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## 1966gtoman (Dec 21, 2015)

Oldskool,

I looked at those but was hesitant on which size to use. Thanks for the advice, they are now on order.


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## geeteeohguy (Feb 2, 2008)

I'm with oldskool on the difference side-to-side being a non-issue. Assemble it and run it.


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