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To get into acceptable or optimized squish/quench with aluminum heads the piston to deck clearance of GM spec of .025 combined with the thinnest of available composite head gaskets is .026-.028 inch compressed. So using spec clearance of .025 plus gasket thickness of .026 to .028 the total clearance is .051 to .053 where we‘re looking for .035 to .045 inch.

So if you deck the block to .016 you buy space to bring that clearance of .051/.053 back into .042 to .044 inch. If he zero decked the block he can totally control the squish/quench clearance with gasket thickness selection.

All of this is somewhat theoretical as taking specific measurements by cylinder shows that the manufacturing tolerances of exactly where each crank pin measures from the crank centerline, the length of each connecting rod, the true position of the wrist pin bore of the pistons, angularity of the main saddle bores in three dimensional space, the conformity of the deck plain with the crank center line all have an affect on the exact distance any one piston sits from the head deck. So while we talk in near absolutes about squish/quench clearance the reality is without careful blueprinting hitting the theoretical desirable is a rather random affair.

I guess the theory of “precisely wrong but approximately correct” holds sway here. Ya do what ya can but that doesn’t mean letting any more slop get into the build than absolutely unavoidable. But there are many other unavoidables a classic is intake manifolds with a carb or TBI where both the air flow in CFM’s varies runner to runner often by a lot, as does the AFR. So there are a lot of reasons as to why cylinder to cylinder power and detonation sensitivity are not equal.

Bogie
 

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Ive cut decks from 8.990 to 9.035 and not had intake sealing issues with the deck if perpendicular to that 90'. What I'm saying here, is if the decks were cut at more than 90, or less than 90, the heads intake interface could be sealing the top or bottom of the ports but leaving a gap at the top or bottom. I do not expect this to be the issues however it's a easy thing to check since the intake is off already anyway.
The second thing I'm wondering is if the intake has a crack that open under clamp loads going unnoticed.
These things are so hard to diagnose without seeing it in person.
 

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Discussion Starter · #83 · (Edited)
Bogie I don't know how else to answer your question but yes the dowel pins are in the block that locate the cylinder heads as I had the machine shop install them along with all the other ones. As far as my intake having a crack in it the answer is no. This has done this with three different intake and all three brand new from the start and never any used ones. The air gap was brand new when installed I think two years ago on the previous build.

I had no problems with it or the heads and even getting a little loose on the bolts before I retorqued them after a few heat cycles and never any problems. Then swapped the heads and same air gap intake over to this build and it leaked from day one. Took it off and tried again same thing.Would weep after sitting and only in the front. Had other running issues which some on this post know what I am talking about. Then sold the air gap and put on performer rpm and it sealed for three weeks on one side and six weeks on the other. Took it off and tried to seal it and failed in short order.

Then stuck the brand new eps intake on which I had on hand and sold my performer rpm as needed green because of this dang problem taking my green out my pocket faster it comes in. Anyway this time I did not even get one day and not even a chance to run it. Was dry but as soon as the antifreeze was filled and planed to start it the next day, well I saw the antifreeze bubbled up to the top and the front gaskets soaking up and was dark gray and I thought many words I can't type here.

I then left it and the next day the gaskets was soaked back about another half of an inch from the previous day. Because the front gasket was so dang soaked it lost some torque. I also could push the steel shim part up sticking out past the intake up towards the valve cover back and forth a hair towards the cylinder head surface at the front right before the intake runners. I could not produce that in the rear from what my old eyes could see but perhaps the gasket being soaked played a part in it as the rears was always dry on all the previous attempts. The antifreeze would also leak out the front angle part in the front and drop down onto my Water pump and it did this with all three intakes.


I put a white paper towel on the pump top and it was verified it was the intake and not the pump gaskets. Paper towel had tiny drops where it soaked from the intake.

I forgot to note that and thought it was my water pump gaskets but I wiped it clean and after taking my previous intake off it was always dry and then I installed this one and the next day when I saw the antifreeze on top of the front coolant port intake area of the gaskets I noticed it on the front angle to where it goes flat on the china wall it some how would end up dribbling down and then spot on my water pump.

As I showed earlier it is slowly traveling down towards the back as it sits and end up into my intake runner. Its almost like the front of the engine is loose and won't go tight and the rear is tight enough to stayed sealed. The intake valves were filled up at least an 1/16th of an inch all the way around the valves that were closed. It has since evaporated away some since its got open air available and with me hunching over my Notre Dame back which I am getting from measuring so many things on this build.

You may or not be surprised with my other findings but I need to make my notes better so I can post the photos. Since this intake was torqued the clearance changed from before. Something tells me the block is somehow been messed up in the decking process as the heads worked fine before on previous short block and with same intake with same brand gaskets.
 

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Discussion Starter · #84 ·
Ok here are my findings and hope you can understand how I wrote it down. I took my intake and put it on and then put in four bolts in the next to last for corner bolts. I just finger tightened them so it would not move. I noticed just by tightening the bolts with my fingers would change things a hair. This is with no gaskets.

This is not bullet proof but I think my findings are showing something here. The first photo which is a horrible drawing of an intake shows the china wall clearances from side to side. The next photo shows the angle clearances as best as I can get.

In photo one you can see a big zero. That means I could not get a .0015 feeler gauge underneath the intake from the head to where the line ends. Then I could fit a .0015 feeler gauge after that and the sizes can go up bigger as it get closer to the driver side. I could get .003 to .004 starting off and could get that to my oil pressure port area. Could not get a reading straight there as my port has my gauge hook up there. Then at the farthest corner right beside the head going straight in about the width of my feeler gauge I could get clear up to .011. Beyond the thickness of the width of the feeler gauge it gets tighter from that part back towards the passenger side really quick.

On the front from the driver side its about .002 up to where you see the marking where the .004 starts. Its kind of hard on that area as I had a few dings from when I had to use a screw driver to pickup the intake when taking it off and the feeler gauge will get caught on it. Then you can see I can get .004 the furthest from the passenger side. Then I can only get .005 even lesser from the passenger side then even less with .008 then even less with .010. Then the thickest I could fit was about .012 of the width of the feeler gauge and could not slide it any further.

So in the photos you can see where the rear driver side has a lot more clearance especially the one spot furthest towards the angle of the head starting point and gets way tighter towards the middle and way tight after that.

Then the opposite in the front. Driver side starts off super tight and then gets more clearance the further it goes out towards the passenger side.

Then moving on to the angle clearances front and back. On the front on the passenger side you can see I could only get about .002 from the bottom to only half way up the intake flange. Then a .0015 I could get up about half way and that was it. On the driver side I could get .003 up almost half from the bottom up. Then .002 about a hair past half. Then a .0015 most of the way up. Sad to say on the back part I could not get anything on it. I loosened up the rear bolts and let the intake drop on the .0015 feeler gauge it was a very tight drag.

Now on the china wall clearances if I pushed it forward some then the clearances would change somewhat in the back and I could fit a feeler guage all the way across on the zero area. But that was with the bolt holes not being centered as much as possible though. The same thing with the front and if I just ever so slightly moved it a hair on the side it would change the china wall clearance just a hair as well but not nothing drastically different.

On the intake I used a straight edge and the end surfaces are as flat as can be and a .0015 feeler gauge had a good feel all the way across. Same with the flanges they are nice and flat and within a .001 difference from front to back and nice tight drag at many different angles. Now on the china walls before I torqued the intake down with it sitting on gaskets it had about .095 and felt about equal across both china walls front and back. The same was with the previous intake that was used and had already been torqued and through heat cycles.

That was in previous posts and don't know if that makes any difference or not. Just moving this thing a hair by sliding it front and back a hair changed things a bit. I did my best. I did a second test and the specs were withing about .002 of these findings. I do however don't know how I did it but the biggest open area the driver side rear which was .011 I actually one time yesterday got a .019 but forget what all I was doing when checking things and did not get that reading again.

Since it was torqued it did change things from my previous posts.
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Eric, I think you are correct about the block deck being off, as you state in post 83, unless you had heads cleaned up before installing on this build, did you have heads cleaned up?

But what doesn't make sense is that if there is a gap at top of front intake water port, is why gap is not closed up by silicon around water port.

Even more is why it leaks with out even running the car, there is no pressure on the cooling system. this fact makes me think your heads have a porosity issue or that when you torque intake something is being stressed and a crack opens up, but seeing it is on both sides or both heads. This points back to the block deck angle and a gap that is not being closed/bridged by silicone by water port.
 

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Discussion Starter · #86 · (Edited)
95truck I agree something is off and it has to be the block. The heads were never flat milled or angle milled. The heads along with two different intakes sealed fine on my old build which was only two years old before I sold it. I kept the complete top end and cam etc and moved it over to this short block and since day one the problem can not be fixed and don't matter what intake I put on it or how I do up the gaskets it leaks period.

Not only is the coolant soaking up into my gasket and trailing its way back into my intake runners as you can see in the photos I posted, it also will weep out the front area and then drip down on to water pump with a few drips. I could take my finger and wipe it underneath the lip angle on the front of my intake and get antifreeze on my finger. The intake I just stuck on the first day I put antifreeze in it which was the afternoon time and less then 12 hours later the antifreeze leaked out and dripped some on my water pump and the intake gasket was soaked from front back towards the front intake runners and then I left it and the next day it soaked up even more as you can see in the photos.

I had to drain it at that point as I did not know it was going to get into my valley area or not but I expect over time it eventually would have as it already made its way into my intake ports. I have at least an 1/8 inch circle of antifreeze sitting around my intake valves that are closed.

I have been looking to maybe get a temporary motor to put in my truck while I can eventually pull this out as at this point it needs to be taken out and then check to see how far the pistons are in the holes and then go from there but on finding an engine nobody has just a bone stock 350 small block engine that I can buy. I need to have something in my truck so I can drive it while the other build is going to hopefully be fixable if its the block which I feel at this point it is and I will have to wait and save for that part and if the block is unable to be fixed then I will have to wait until next year to get a block with the way things looks as many parts are back ordered and shipping dates keep moving forward.

Jegs or nobody has anything which is sad and I live in a tiny town and junk yards don't have anything around here older then ten years old and not much luck being able to score something. Then top it off even if I did find something I can't pick it up as my truck is down because of this. Just a crate bone stock 350 that takes an old school mechanical fuel pump would be all I need at this point to hold me over.
 

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Eric, keep eye on Facebook marketplace, I see stuff there all the time. Also I bet if you find one and go look at it, odds are you can work a deal with a guy to deliver. Another option would be to rent a pick up from Home Depot or U-Haul for the day while you haul it home.
 

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Discussion Starter · #88 ·
Heck I never knew you could rent a truck. I know a uhaul truck. Thanks 95truck for the info. I actually did find a guy who is close to me that has a used 350 that he said came out of a dump truck and its an early 80's model as I can tell by the cylinder heads as its a pre 86 style outer perimeter valve cover bolt pattern and it has a Qjet sitting on top and I can use a mechanical fuel pump on it so it would be a basically bolt in and go if its good.

Claimed it was low mileage and had no smoking or knocking and has only sat for a year. I have never bought aused motor before with it not running and would not know what all to look for and check out before buying it if I decide to. I have another one to possibly get but don't know if the guy will sell it or not but it was a new rebuilt stock motor that was in a boat but it overheated twice and the last my Father had it ran he said it had no smoke coming out the exhaust and was running good and sounded fine and snappy still.

He said it over heated the first time and they let it cool down and then idled it back to shore but was not under load. The second time it got hot and they let it sit and cool down but it was not ran after that over heat and it was towed back to shore. He only ran it for a brief time in his drive way and said it sounded ok and said it might still be fine but don't know without looking at it.

I don't know how much a small block chevy can take overheating wise. He said it got up to 250 for a brief period.
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Ya know for 50 to a 100 bucks I’d take a chance on it. Basically considering it’s history I’d treat it as 500 pounds of scrap iron I think the current rate is about 7 cents a pound.

I think rebuilder cores for a 350 is about 350 dollars for a long block.

Bogie
 
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