Thread: Decked?

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I know I have posted a few times already, but like I said I am a newbie, and this next question may seem elementary but I cant learn if I dont ask.
Would someone be so kind to explain to me what exactly it means to 'deck' a block?
I appreciate all the help yall have given so far.

You take a light cut of metal off the deck surface of the block (where the heads bolt to the block) in order to set the squish (piston to head clearance).

When the manufacturer built the motor originally, they left the piston down in the bore slightly (maybe 0.025" to 0.075") with the piston at top dead center. Adding the head gasket thickness to this figure leaves the piston too far down in the bore at top dead center (maybe 0.070" to 0.120") to "squish" the mixture across the chamber for proper mixing when the piston comes up to the squish pad on the cylinder head. The tighter you can get the squish, the better the motor will run and the less it will be likely to ping on cheap gas. Most builders will shoot for a squish of 0.035" to 0.045". That means, for instance, if you are using a 0.040" thick head gasket, that you would want the piston crown to be at zero deck, or even with the deck at TDC. That would leave a clearance of 0.040" between the piston crown and the head (it will be less than that because rods stretch and the crank flexes) so that the piston will just barely miss crashing into the head at TDC and will give the mixture a maximum "shot" across the chamber.

To do this properly, you'd use only one piston/rod assembly and you'd assemble it on the crank at the four corners of the motor, one at a time of course. You'd measure the distance from the piston crown to the top of the block deck at TDC and record these figures. I've never yet found a block that was square, they're always off at least a few thousandths. Anyway, lets say that the block is square and that your measurements are 0.035" on all corners. You would then remove the piston/rod assembly, the crank and bearings and take the block to your machinist, telling him how much to "deck" the block so that you had the desired zero deck or wherever you wanted the piston to be at TDC.

If you were going for 0.040" squish and using a 0.040" gasket, you'd tell him to cut the decks 0.035". If you were going for 0.040" squish and using a 0.018" shim gasket, you'd tell him to cut the decks 0.013". That would leave the piston 0.022" down in the hole. Adding the 0.022" to the 0.018" gasket thickness would yield a squish of 0.040"

It should also be noted that you don't have to run a 'zero' deck. Depending on your build, having a deck clearance can be beneficial, such as in a forced induction (turbo, supercharger, etc.) project. It can be used to square a block the was slightly miscast, or in the case of aluminum, warped.

In either case, it is good to have this done to make sure all surfaces are square to the crankshaft. It will helpkeep the volumn of the cylinders consistant from cylinder to cylinder, much like having the head surfaced and cc'd.

Keep in mind that if having the block decked is to increase the compression like the example above, this can change the way the intake mounts to the heads (in a 'V' configuiration) and may require to intake also be machined. In the case of an inline engine, this can cause issues with OHC timing belts and chains because you will have decreased the distance between the crank sprocket and cam sproket.

Thank you very much. So then on that note, what is the best way to go, with a .040 gasket, or a shim? Also, if the rod stretches and you had it decked to zero deck, wouldn't that increase the likelyhood of the piston hitting the head?

Before you deck the block, you want to find out what your options are for head gasket thicknesses, then you can determine how much to deck it to reach your target of 0.035" to 0.045" squish figure. I was just using these 2 thicknesses as examples. You may have a choice of 3, 4 or 5 different thicknesses from which to choose, so then it's up to you to do the math and determine how much you will deck the block based on the gasket you have chosen.

Zero deck means that you still have the thickness of the head gasket between the piston crown and the head.

If you have a large bore motor where there may be more piston rock in the bore, or if you're using forged pistons with a considerable piston to bore clearance, you might want to use a squish of closer to 0.045". If you have a small bore motor or are using cast or hypereutectic pistons with a tight piston to bore clearance, you might get away with tightening the squish up to 0.035". I've talked to some engine builders who run tighter than that, but I won't recommend it on this board.

I just finished my 505 stroker. I had it squared and decked, he left my pistons .005 in the hole. Im using a .038 thick gasket, so I'll be at .043. You have to figure where you want to be with compression ratio, then go from there. I personally dont care for the steel shim gaskets, they're thinner but some have a problem getting them to seal well. I dont want any problems in this area, so I'll stick with a composite gasket. They usually range from .038 or so to .051 or a little more.

for a mild big block i woud not 0 deck it getting it squared is more what you want 00.5 to 0.10 the piston in the hole tru deckAnd go bore it this keep the bore strait to the deck and the deck squared to cam and crank center line .you can then put one piston and rod and check all corners BUT do you know all the rods are the same????are the pistons the same ??? are the crank pins the same index rods get recon and cranks get cut and i know cranks that have been off set to save them.and rods do get shorter and if it cast top piston they are not the same the new rods and piston that are cnc will help but you will have to check it and i would use a 0.39thick head gaskets

"BUT do you know all the rods are the same????"

That's why I said this in the post above.....

To do this properly, you'd use only one piston/rod assembly and you'd assemble it on the crank at the four corners of the motor, one at a time of course.

i deck with a b.h.j block-tru deck kit and the deck .005 to 0.010 i would try to keep it .005 and no more than 0.010 sorry i did not put the decimal mark in the rigth spot on the last post

I did not say you did not techinspector1 but did you talke about the crank and the pistons????

The best thing to do is find a good machine shop take your hardware to them tell them what you want and dont want if he's
any good he will talk everything over with you. first off you will need all the rods, pistons, pins, crank, and all bearings. this will
insure a good fit for your parts also a good machine shop will take in consideration of the oil that will be on the bearings just like when your balancing a crank and rods. The only need to go zero deck is to gain comp. and you are also getting very little amount of torque with it as well. also you pistons shoud match you heads so you get a good better burn.

i deck all blocks why?? so they are square and the deck has the right finsh on it. new engines have a bad finsh on them and they will not hold the head gasket this gets real bad when the cr gose up. on a hp build i use the b.h.j blok- tru this make the deck rigth if the engine buider dose not go off cam and crank centers like the b.h.j dose the deck will not be at the rigth angle and if he set the boring bar off the deck the piston walls will be off. this is the start of a good build and rigth here is where to make it rigth. a good engine builder know this . if you have not done a lot of big blocks find some one with a good rep with big blocks and fine someone to do the work and get the parts from the guy so you get it rigth and use the stuff he like to use .this may help but this is the start. there is a lot of things to think about like oil clearance and the rigth length pushrods piston to wall clearance piston to vavles and a lot of things.