Is decking worth the money

[MT Jeff]

I'm building a new engine for my boat, it is .030 over 350 sbc with 76cc heads. It is at machine shop now. I'm using a 1.56 comp height speed pro flat top piston in an uncut block which should put it at .025 below deck. If i used a .028 GM gasket it should put the quench (squish) clearence at .053. The machine shop gets $150 to deck the block. Would this be worth it on a 9:1 or less engine? I could get is closer with a shim gasket but I really don't want to retorque it in the boat. BTW it is a closed cooling sytem not raw water cooled. I guess what i'm asking is it worth it for .010"

[1989TransAm]

If it was me I would take .013" off of the deck.

[rob vine]

decking the block , if done properly sets the deck height equally on both sides and end to end and gives a nice flat ,clean surface for the head gaskets to seal on and prevent leaks , compression and water

[rubberweasel]

generally, how much is an average sbc block off on deck heights... .005"..... .010" ???

[rob vine]

i use a bhj setup and have found small block chevs to be anywhere from .013 side to side and up to .032 end to end and eveywhere in between , generally i find small block fords and big block mopar to be pretty good , within a few thou .

[MT Jeff]

generally, how much is an average sbc block off on deck heights... .005"..... .010" ???

I don't know personaly the machine shop say most they check are between 9.020 and 9.025.

[Alan Roehrich]

Most OE Chevy small blocks are around the 9.025" spec deck height. Most aftermarket performance pistons are made to work with a 9.00" deck height.

The correct deck clearance is worth power, as is correcting errors, such as the decks not being 90 degrees apart, the decks not being equal, and the decks being off from end to end.

I'd set the deck height to 0.00" and use a FelPro marine gasket with 0.038" to 0.042" thickness.

[racear2865]

I am lucky in that I have a CNC mill and I get to check all 4 corners and keep a record. When I first started actually looking at the numbers. I was amazed out how far off the numbers were, especially end to end. But I found one other problem that hasnt been mentioned yet and that is the decks very seldom are 90 degrees from each other. Most customers dont want to pay for decking until I show them how far off the decks are. If they are not in my shop, I call them while the block is still chucked up and tell them. Over 50 percent will say correct it. Most decks for SBC are at least .015 off from the 9 inch number. I make them a copy of where the block was and where it is when I am complete. I give it to them when they pick up their block. Turns out to be a good selling or bragging point. Good selling for me but bragging for them
reed

[340king]

I agree with the previous posts and want to add one more thing to consider. I would have them deck the block with a block true fixture prior to boring the block. Most boring bars use the deck as a reference point and the crankshaft centerline as the other. If the deck is not at 45° to the crank/camshaft line, then the new bores will not be perpendicular to the proper deck surface. So what I am saying is the order of operation is important and should be considered when the work is accomplished. I am just trying to get you the most out of the work you are paying for.

[PackardV8]

Yes, decking is worth the money. It's doubly worth the money if done with a block-truing fixture which insures the decks are phased properly.

No, today I wouldn't pay anyone to build a precision engine using a boring bar which sits on the deck. That's old school for budget stock rebuilds. If that's all one has, then agree, the block should be deck-trued first. Back in the bad old days, I built race engines with a block-mounted bar and a back-stroked hone, but not any more.

Maybe, decide what are your goals and your budget. IMHO, that $150 is a good investment. BTW, you will have them line hone the block before it's going on the mill, won't you? Another good investment.

jack vines

[drifter]

Wow i find sb chevy mabey .005 or so out and BB mopars some times large amounts like .014 from end to end at times

[ProPower engines]

The more important reason besides keeping the deck heights dquare and true from side to side is you need between
.035 and .040 total deck to help prevent detonation.
This may seem strange but without going into a long post go to the KB web site and read why it is so important
It goes into great detail and is easy to understand why its done that way and the benifits of doing so.

The short story is it helps cool the exhaust side of the chamber. and while reducing compression with a thicker head gasket is not really the best way to acheive the correction in this case.

But yes have them do a deck job so both side are the same and leave them .010 down in the hole and use the .028 gasket and you will be golden

[Truckedup]

I'm no expert ...But any decking for quench should be done after an engine mock up so you know how much to cut .......

[wyrmrider]

X2 truckstop
Usually BB Mopars are ok but the one I have in my motorhome was too far off to clean up and sell, the pistons ended up .015 out of the hole
a quick check is to install the four end pistons and mic the deck, check both intake and exhaust side if you wish
this will not check if the bores/ decks are 90 degrees to each others
those that posted the solution above gave the OP excellent advice
I deck to 9.015 sop
IMHO the measurements given in the literature are the minimums, also what NHRA would consider minimums, what you would cut to to the maximum legal compression/ dimensions
do read the info on the KB website
or out ten with an .040 gasket
remember 340 chryslers (and others) came with above block deck piston heights

[ProPower engines]

I'm no expert ...But any decking for quench should be done after an engine mock up so you know how much to cut .......

Unless you have a way to measure the block and do the math based on the rods piston comp height and stroke being used.
Then a mock up to check the deck heights is not required.
But agreed this calculation is done before hand to know the required amounts to remove from each side.