Quench 318 with stock rods

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73beast

73beast

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So I'm running a 318 with kb167 pistons. and with stock rods my deck height varrys from .0035 above the deck to .008 below the deck (.0115 variance) depending on the cylinder. I have already rearranged the piston/rod combos to the most ideal cylinder, longest rod to the tallest deck cyl. and shortest rod to shortest deck. I measured with a dial indicator on a magnetic base arm and zero'd it to the deck, measured each from multiple mount points and each cylinder measured within a range of .0025" or so (ie. the tallest piston is #4 measurements varried from .00125 to .0035 above the deck by pushing up/down on the piston and different mount points, and the shortest was #3 from .0055 to .008 below the deck).
Should I be worried about this differance of rod lengths?

Anyway I'm getting close to finishing this engine up ( just need heads and cam). more info on my build at a previous thread: http://www.forabodiesonly.com/mopar/showthread.php?t=212457
just throwing out my used cam and going with the smallest of the solid/flat voodoo cams(60440) or xtreme energy cams(20-230-4), both seem similar.

I am looking at the felpro 1008 gasket with the edelbrock rpm heads which would bring my piston to head clearance between .0355 and .047 depending on which cylinder assuming i get exactly .039 compressed thickness from the gasket. Which from what ive seen in my research is pretty wide range for a quench benefit, meaning little-no benifit on the shorter rod'd cylinders. I've already had the rotating assemply balanced so i dont want to switch out the rods now... But I would appreciate advice.
 
Btw my machine shop guy milled the deck lightly only to square it out. and after i did a 4-corner deck measurment using the same rod/piston and got:
cyl# / deck height
8 / 0 to .002 below deck
7 / .0035 below to .005 below
2 / .005 above to .0035 above
1 / .00025 below to .0018 above
 
Your machinist may have milled the decks to be "square" or 90 degrees from each other, but either the crank bore wasn't used as a reference, or the crank shaft was ground by monkeys. Were the rods resized?

You list two measurements for each piston is that difference fore-aft? Pistons will rock slightly in their bores. Inserting a feeler gauge between the piston and the bore at 12 o' clock should make this more consistent.

To me it sounds like the block was just skimmed. That is, it was just loaded in the machine and an even pass taken off each deck surface. The blocks left the factory cut that sloppy, and cast iron moves as it seasons, but if you're spending the bucks to do a quality rebuild it sure is nice to improve things a bit.
 
piston rocking accounts for .0005" or so with my pistons. but the reason for 2 measurements is mainly the oil clearances, and measurement accuracy due to differing points of measurement. at any given point (with no crank movement) i can move a piston up & down about .002" by hand. giving me a range of possible heights. so I could assume with a constant oil film it will always be at the center of my measurements. But I dont like to assume.
& rods were not resized. I even sent them back for tight rod oil clearance (i used plasticrap) but his measurement was .0017 to .0018 clearance, and he was ok with that.
 
Start with having the crank indexed. Then have your rods checked out. New rods are a cheaper and stronger route. (As a matter of fact, just get new rods!) Re-fit the pistons on the new rods and assemble it with the reground, indexed crank and install. Recheck the pistons height.

If the issue still exists, bring the assembled short block to the machinist to have the block corrected.
 
A few notes - If you are building for quench and using factory parts - all those parts HAVE to be blueprinted. Blueprinted is not refurbished. Blueprinted means all the factory spec dimesnions are matched. Rod length, crank centerline, crnak throw indexing, and crank stroke length, deck height, deck squarenesss - all get done. It's expensive but that's how you enable the parts to run close - and close is what makes quench work. So the varience you have is a combination of the deck being milled (which as Chief said is not squaring up or square decking), the crank not being indexed and corrected, and the rod lengths adding up to error. If you were using an open chamber head that each chamber depth can vary, and every chamber volume can vary chamber to chamber, never mind the head gasket surface being parallel to the deck. I don't bother building open chamber quench engines anymore. It's too expensive for the intensive labor required to get it right.
So in terms of your build - .040 is the "magic" number for an effective quench. I would be running that at .030 quench distance. The block's deck would have been square decked, the crank indexed and stroke corrected, and the rods blueprinted to get things right. You can run it as you have it - but the affect is diminished. Whether or not that affects your engine is an unknown but it will not be as good as it could have been.
Oh - edit - like Wild noted - you measure the piston on the pin axis - not the edge. You can check piston rock but if you're running a tight piston to wall (KB hypers do...) and more than .028" I don;t think you'll have any problem.
 
Thanks for the replys! I guess i have to decide if the setback and costs are worth fixing it. But I know if I dont it will bug me every time I drive it.
 
I don't think you have anything to worry about running it as-is. The Comp has more overlap and I don't think you'll have any issue at all with any fuel. With the Lunati I think the quench you will have coupled with the aluminum head material will make it usable. You might need to take some care with the timing and carb setup, or perhaps run pump premium but you should still be ok.
 
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