I have a 383 stroker 4 bolt main right now, i have it all tore down to freshen it up. took it to the machine shop to check it out, deck it fresh, check teh mains' allignment and ballance my rotating assy. with the new .040 pistons. The machinist called me today and said that he ran into a problem. he said that the deck was not flat, in fact it was way off on one side...almost like the machine shop who decked it last time had it cocked in the machine or something, and it was not square witht he cam and all that (im not sure on all the techinical terms) either way, he said it wsa off a lot. He said that to make it flat and square again, he may have to take off as much as .025" more than what has already been taken off....Right now it sits at 0 deck height, right at 9" from the center of the mains. So basically, what i take from it is that the pistons will be out of the hole about .025". First question, is there any thing different on the LT1 block other than the reg. SBC 350 that might throw his measure ment off? he said he was familiar with the LT1's, but i jsut want to make sure. also, is it a good idea to have the piston out of the hole that much?? i know its not wanted usually, but can it be done and what are there any downsides to doing this? I plan on runing AFR 220's so i should have plenty of room to get teh compression i want...around 12.5:1. Or do you think i should get a new block? The machinist said that the measuremetn from front to back was right, but the measurement from the top of the deck tot he bottom wasnt, like it was slanted more on one side (from what i could get from it on the phone.) is there anything that could've caused this or is it just poor machine work at teh place i had do it last time? i dotn know what the block has been through in the past, but i know i got it out of a vette in the junkyard, and nothing catastrophical has happened to the block since ive had it in my posession. thanks for your help and suggestions in advance

Chad

 

Well first off, you cna't really correct the quench height on a LT1 if the pistons are out of the hole .025, just not enough gasket selection. So that's not a good idea on that block.

The deck is perpendicular to the crank centerline, maybe the mains were not line honed.bored straight.

I would ask him how far each corner piston (1,2,7,8) are down in the hole. That's the key.

I'm trying to figure out what he was talking about when you say

"but the measurement from the top of the deck tot he bottom wasnt, like it was slanted more on one side "

That's a bit iffy to me. I just want that clarified before I say anything.

Funny thing is I ran into some of the same problems on a motor I have in house now. Decks and all sorts of problems with another shops block work. Makes me sick to thing guys are that bad at this.

Bret

 

Floors in shops can settle and cause bad "stuff" to happen.
When I was spending 19 years doing the injection molding machine repair and mold set up we had every piece
of machinery checked for level once a year. It means alot to stay on top of it!. Its a little cost out of pocket for a shop but pays in the long run.
Not say'n the guy running a given machine operation can't f-up in his methods or process because we all know that happens.
I like to see a clean shop and one with cert / calibration stickers on the equipment if you know what your looking at.
Now days if a machine shop or mold shop in my experances is doing work for OE manufactures they are on top of a PM program.

just rambl'n

we have saved torched blocks from bad burns between cylinders on the deck by getting it re cut but this requires custom pistons with the wristpin hight moved higher so to drop the piston back in the bore where its need to be. Costly repair and only done in my opinion when pistons are all ready damaged and your having to replace them.

...but buying custom cnc pistons is what i'm use to
might be to costly compared to another block.

QUESTION
So were you saying the deck machined with taper?

 

I 'll see if i can better explain this, but its hard to do without me actually seeing the problem (ill check it out tomorrow)

He said that the mains measured out straight, because i asked if that could've beent eh problem.

lets say that you are looking at the side of the drivers side of the block. From what i get from him telling me, that the deck was perfectly level from teh front to the back of the block, BUT, when it came to the deck being 90 degrees with the crank, or perpendicular, it wasnt. so looking at it from the front of the block, he said that one side (i think the pass side) was slanted downhill more and the drivers side was slanted the other way. does that help or hurt your idea of what im saying? basically, it seems that the shop that did the work for me before had the block crooked in the machine (cocked slightly clockwise maybe?) so i guess if this turns out to be true, im pretty much screwed and need to find a new block right? what do you think would be the MAX i would want the pistion to be out of the hole? (just in case its not as far off as we think it is and wont require as much taken off the deck) thanks

Chad
PS yes hotrod, i think that it was decked with a taper, or something somewhat like that. And i havent bought the .040 pistons yet, so some custom pistons may be an option..and downsides to them?

 

OK

So the face of the deck is not perpendicular with the bore?

It almost sounds like it was core shift or maybe the boring bar was not set up at 45degs.

Very odd.

Bret

 

I dont know if this is true, but wouldnt a piston being out of the hole that far cause more rocking of it? Since you lose quite a bit of surface area on the wall. Also depending on your piston selection, be sure the ring isnt even close to poppin out! If theyre like my blower/nitrous pistons you wouldnt have a problem since theres about 1/2" of ring land before the top ring, but id assume flat tops dont have near that much land there. My comments should be corrected by Bret BTW, just bringing up more thoughts.

 

Well most rings are far enough down the piston to not have a +.025 deck height problem.

The skirt is the only area that touches the bore of the block. If you look at a piston closely you will notice that the ring land area is not as large in diameter as the skirt area, so that doesnt really play into it.

I was mostly worried about the fact that the piston will touch the cylinder head because there will not be enough clearance.

Bret

 

Bret, you explained it so easy thats what i get from it anyway, and i think it is pretty odd myself...sucks on my part though. I guess i'll get more info on it tomorrow *hopefully* it may not be as bad as first thought.
I was thinking about this a little and had another question. With the block the way it is now, how would that affect the performance of the engine, if any. from a beginner's thinking (me) it seems it would throw off degreeing the cam, valve timing, valve angles and all that. do you think that this would have and adverse effect on HP?
Also, the stock head gasket thickness is .049", i believe, would this be enough space between the piston sticking out of the hole .025" and the head? If not, would it be stupid to have a custom head gasket made by someone like Cometic to make up for the clearance prob, or wouldthis be a bad idea to do?

 

You are going to need a different block or custom pistons. A deck of +.025" is too much. A gasket thick enough to compensate and get the desired quench will be weak.

Rich Krause

 

anybody have any suggestions on who or where i can go for custom pistons? and are there any downfalls to having the pin moved up higher on the piston?

 

Quench should be about .035-.040 ideally, no less but you can have up to .060 but it's not as optimum. More is worse but less is DANGER

Quench = how much piston is in or out of the hole + compressed gasket thickness.

So even with a .049 + (-.025) Because it's out of the block you will be at .024 so you still need another .011 at the most. Don't stack two gaskets that's a big no no.

"I was thinking about this a little and had another question. With the block the way it is now, how would that affect the performance of the engine, if any. from a beginner's thinking (me) it seems it would throw off degreeing the cam, valve timing, valve angles and all that. do you think that this would have and adverse effect on HP?"

Good thought. One reason why a proper block is worth HP because it's done right. A CNC Bowtie block is great because it makes sure everything is in the right place. That keeps all the events happening at the right time, piston at TDC at the right time, cam vs crank are in line, lifter bores at the right angles and at the right spots, everything. 20-30hp is easy to find in a properly machined block over a improper one. That grows even more if it's a hot honed block and more still if that block is aluminum. Hot honing and aluminum go hand in hand, the bore roundness gets worse at a multiple of 3 over a iron block because the aluminum block expands 3 times faster. That is all money though. When you are racing a SBC though a 4 bolt Sportsman CNC block is around $1700. Getting a 4 bolt old school core to that level is going to add up to about that much and you still can't be positive that the cam and crank are parallel with each other, well at least not easily. Plus you start out with a stronger block when you have a Bowtie.

OK I'm off that horse now. Back to the wonderfull world of stock LT1 blocks now.

Bret

 

What is the compression height of the piston you are running right now?

5.7 or 6" rods?

Custom pistons are very expensive, but in your case so is a new block, hopefully for you neither will be necessary.

 

Looking at the blocks in Jegs/Summit they seem so expensive, but now looking at it, if you think about it, it requires over $1000 easily to take a stock LT1 to accept a stroker crank (done right at least), and thats a GOOD price from what Ive found.

And when those CNC bowties come ready to go with a hone right? Thats not all bad considering you will spend ~$300 on a good LT1 block, and who knows how everything lines up in there..

My next project will surely include a CNC block, especially after hearing Bret say the potential HP involved with a good block. Also you dont have to find a good machine shop if you are young and dont have experience with shops.

Ok sorry, Ill stay off that horse as well, back to .025 out of the hole.

 

If you are talking a high quality piston in the first place, a "custom" compression height is not really much more expensive than an off the shelf piston. I just bought a set of JE's with a custom diameter and custom compression height. ~$80 more than an off the shelf piston from the same line.

Rich Krause

 

Hmm, guess I thought they were more than that. That still ends up a $600+ set of pistons, but you still cant get a new block and make it a stroker block for that much, so this would be your best route assuming a really short compression height isnt a bad thing???