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Old 12-19-2012, 02:47 PM
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Before you do anything, measure the piston deck clearance so I can compute your SCR. Here's how with cheap tools. All you need is a 6" or 12" steel rule and a set of feeler gauges. Bring any piston up to top dead center, stand the rule on edge about 1/4" from the edge of the bore at the 3 O'clock or 9 O'clock position as you are standing at the side of the short block. Trying to find the piston deck height with the steel rule placed at Noon or 6 O'clock will allow the piston to rock back and forth on its wrist pin and will give you false information. Stack feeler gauge blades together until you get a snug fit between the piston crown and the bottom of the rule. Hold the rule down firmly to the block deck, making absolutely certain that there is no air gap between the block deck and the bottom of the rule. Have a helper rock the crank back and forth a little clockwise and counter-clockwise to insure that the piston is at exact top dead center. Measure, re-measure and re-re-measure. I would do this on each corner of the deck, in other words on cylinders 1, 2, 7 and 8. In this way, you'll be able to find any discrepancy in the piston deck height, meaning that either the block needs to by cut to make the block decks parallel with the main bearing bore or one or more of the stack of parts (cylinder to cylinder) are not the same height. If the block decks are skewed (uphill/downhill) or not the same cylinder to cylinder, then the static compression ratio will be different from cylinder to cylinder. If you end up with an "on the edge" build with one or more cylinders making more cylinder pressure than the others, you could have detonation on those one or two cylinders while the rest of the cylinders are singing along happily. It's even possible that some of the pistons are 1.560" and some of them are 1.540". You have no idea until you measure the piston deck height as outlined above. With this simple procedure, you'll probably find that the corner to corner dimensions are off enough to make a problem. You can, of course, put the motor together without knowing any of this and it will run, but if you want the best performance from your build, you have to jump through some hoops.

My standard operating procedure includes align-honing or align-boring the main bearing bore, cutting the block decks to parallel with the main bearing bore, with the height of the deck being dependant on the stack of parts being used, along with the gasket dimensions and chamber volumes, then boring and honing the cylinders for new pistons that will work with my combination using torque plates, followed by a trial assembly where everything is measured before final assembly. That's how I do it. You can do it any way you wish or you can buy a crate motor and forget it.

Last edited by techinspector1; 12-19-2012 at 02:56 PM.
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