Im just in the process of doing a motor Freshen-up.The block went of today for machining for new lightweight fully machined `eutectic pistons,they also have a antifriction coating on the skirts,they spec a 1thou clearence,but i found the instructions not to clear as they said to include the coating in this measurement.So am i right in pressuming that this is 1 thou clearence measured on the coated part of the skirt?They are speed pro pistons.My second question is I am having my block decked true at the same time,i have requested 20thou to be removed,this should give me about 42thou clearence?Do I have to also have my inlet manifold milled,and by how much?I am sure I have seen a formula somewhere but I cannot find it anywhere.Any help would be very much appreciated.

Heres the thing. Your machine shop should be doing the work with your pistons. He should make sure its bores and honed enough for your specific pistons. Second as for decking the block. If I were you to just tell them to square it off (what compression are you looking for?). If you tell him to take a certain amount off and you put it together who know if pistons will be in the hole or what. To truely "0" deck a block he need to mock up the rotating assembly in the block and measure.

We have machined a lot of blocks and NEVER had to mock one up yet as we use a CNC machine to do our work and if your dealing with a machine shop that has to mock up a rotator you should find a shop that has the proper equipment to do the job right.

We deal with machine shops all over the country and the to never mock anything up.

check this link to anser you question
http://home.isoa.net/~mharrisj/mill.html

<font face="Arial,Verdana" size="2">Originally posted by CNC BLOCKS:
We have machined a lot of blocks and NEVER had to mock one up yet as we use a CNC machine to do our work and if your dealing with a machine shop that has to mock up a rotator you should find a shop that has the proper equipment to do the job right.

We deal with machine shops all over the country and the to never mock anything up.

check this link to anser you question
http://home.isoa.net/~mharrisj/mill.html</font>


Something is admiss than. My machine shop has the CNC equipment and yes you can "0" deck a block without mocking it up but where is zero? You really dont know unless you put it together. I know everyone has there own ways of doing stuff. But you are one out of a few shops that doesnt do it. Personally it makes sense to me I dont want someone to over chop my block

I am gonna side with badazz on this one. What happens if the block was already milled once? We mock them up to see where we are starting from. And for the most part all we do is square them up. Of course there are some people that demand the zero decking. Jeff

Hi Guys,thanks for your answers so far,I do agree with the mock up proceedure 100%,i did infact check this before i dismantled the engine.It has never been milled or machined.They did vary somewhat,some were -20 some were -30,so i think the decks are tipped.My biggest problem has been trying to find a GOOD machine shop here in the UK,I think I have now they even have a sunnen power hone,and all the jig plates for decking etc of big v8s.My compression will be getting up towards 9.7 -1,this is ok here,as our pump gas is 97-98 octane.The worrying thing is though,they still seemed confused over the piston clearence?Thanks again for your replies.

<font face="Arial,Verdana" size="2">Originally posted by CNC BLOCKS:
We have machined a lot of blocks and NEVER had to mock one up yet as we use a CNC machine to do our work and if your dealing with a machine shop that has to mock up a rotator you should find a shop that has the proper equipment to do the job right. </font>
&lt;p&gt;
I will have to agree with CNC. I'm in an engine shop. When a block is decked square, the deck is surfaced square off of the mains. There is no "zero-ing" of an assembly. &lt;p&gt;

If you want to "zero" an assembly, you will have to take in consideration the faults of the piston forging measurements from the pin center to the lid, as well as the rod forgings from centerline of small to large end. To have a true zero across the deck, you would need to measure each & every piston/rod assembly for total height from end to end, and mix & match for an even distribution from cylinder to cylinder. THEN you would have to flycut the few piston tops that have a long assembled length to match them within a thousandth of the others.
Very time consuming, costly, and not a bit of difference to a standard decking, unless you're in a Nitro funny car class.

If your buying good components and decking a block zero without fitting everthing up should not be a problem as we also own an engine shop and build alot of circle track engines and street and strip engines in the area and have never had trouble with decking a block to zero .

First of all you would have to bore a block first which is not the proper way to machine a performance engine as we deck a lot of blocks and they are no where's near square from the factory as they bore of the pan rail. And now you deck off the mocked up assembly. HMMMMMMM now how sqare are your decks from there.

We ship blocks all over the country and Canada and if I had to have them ship there rotator every time to fit in every block I'm sure I would have been run out of bussiness years ago.

If you take your stroke devide by 2 add your rod lenth and your compression height of your piston that should give you your deck height.

The only thing I can say is the way we deck a block it's done to blue print as the decks are 90 degrees from the main line and 45 degrees from the cam and crank center line. And what are your decks???????????????????????????????????????? now that you decked them of a mocked up assembly. Nor blue print thats for sure. Any of the PERFORMANCE MACHINE SHOPS that I deal with deck as I have descibed.



[This message has been edited by CNC BLOCKS (edited June 05, 2005).]

All I know is what My machine shop told me. Nobody in this town will "0" deck a block with out the internals.

<font face="Arial,Verdana" size="2">Originally posted by badazz81z28:
All I know is what My machine shop told me. Nobody in this town will "0" deck a block with out the internals. </font>

Bore a block before you deck it un heard of. I would say find a real machine shop that does it right instead of backwards

You are the one who does this for a living

The coating thickness on those pistons is roughly .0005" per side. Most of the time they measure the indicated bore size, or at least .0005" smaller than overbore size. If you bore the block .001" over the measured size you are good to go for any application or you can tighten it up .0005" for a mild application. The box normally indicates the recommended bore size as standard oversize to .001" oversize. (eg .030 to .031 overbore) We generally give them .001" clearance over the measured size.

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Custom Auto, your source for quality machine work, cores and new parts at competetive pricing right here in British Columbia 1-888-563-4050
A Canadian, EH? (with a 10 second street car)

I dropped my block off for bottom end machining and assembly Friday... The old man that runs the shop tried to sway me from zero decking the block. His argument was that I could get myself in trouble if there are variances in the rod and piston height, and that he always likes to leave them .015" down in hole.
With detonation in mind with a .039" head gasket, I am going to call him back monday and tell him I want the piston .010" down in hole I think. Considering I have aluminum E-Tec's with vortec style chambers and reverse dome (mirror-image dished) pistons, and around 9.5:1 compression, I doubt I am at any risk for detonation with a .050" quench height.

Thoughts/arguments? Is this my best bet, or should I just tell them to zero it???

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'71 RS/SS project: full roller 406sbc / 9.76:1 w/ E-Tec Al. heads / 750 Competition AFB / big 4 whl discs, 1-5/16 VSE ft & 1" Rancho adj. rr sway bars / 4 speed 3.23 posi / 81 Z28 & dual snorkel vette Air Induction

I'd go for the .020 off the deck. Should have no problems with the intake as long as the heads aren't milled. With a thin gasket, either steel shim or the FelPro 1094, you'll have about .045 to.050 quench. Blocks I've measured have all had some variation in the piston to deck measurement across the top.

If you're running a stock crank (or even lots of aftermarket) then the likelyhood of having all 4 rod pins at exactly the same stroke are slim to none. Piston compression heights are pretty close, rods aren't bad unless they were resized. If you shoot for .005" to .010" negative deck you will have no issues with detonation with aluminum heads and 9.5:1 compression.

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Custom Auto, your source for quality machine work, cores and new parts at competetive pricing right here in British Columbia 1-888-563-4050
A Canadian, EH? (with a 10 second street car)

factory deck heighth from centerline of the crank to the deck is 9.025"And GM uses a 0.018" steel shim gasket
9.042" the crank throw, rod length and piston hieghth add up to 9.000" that leaves a Quench/ clearence for carbon of .042"

ZERO deckers mill the deck to 9.000" and use a .039"-.042" thick gasket.

In ALL reality they have gained nothing.

Many Many thanks to all that replied to my question,its all been very helpful and informative,I just hope the machine shop can do a good job for me!!!!