Has anybody checked after the machining to see the rezults. And how far to shade over? Idealy you would want even thickness . Does this make that hole off line with the crank? Does it effect the ballance? What affect does it have on tbe combustion chamber .
Moving the bore from it's geometrically "correct" location due to thin cylinder wall. Some guys push the boring bar over a little bit to spare the thin spot. Now the cylinder is round and straight, but not where it's supposed to be with regard to the crank and the combustion chamber. Wild Guess 1: GM didn't put the cylinder exactly where it should be, based on production-line tolerances. Wild Guess 2: Moving it over a little more will make zero difference on most builds. Could prevent cylinder cracking, which overall preserves horsepower longer. Wild Guess 3. Machine shops have been doing this "forever", deliberately, or accidentally via carelessness or an inability to locate the boring bar properly. Wild Guess 4: Guys in NAPCAR are moving the cylinders deliberately for their own purposes--less piston thrust friction, geometric advantage through the connecting rod on the first inch of piston travel, whatever they think will provide an advantage.
As long as the fire ring on the head gasket is supported, I figure moving the cylinder is better than scrapping the block. I don't suppose it's optimum, but I bet the real-world results would be hard to confirm with anything less than dyno time or timeslips.
Never a bad idea to maintain as much cylinder wall as possible, in a thin walled casting like the factory 455 is. JW
Hey Jim is there a maximum that you would "shade" a production 455 block? It seems based on the above worksheet that you don't move over more than .015" I guess it depends on the overbore and sonic test?
Mr. Jim, At wat thinness do you decide to shade.? If the machine shop i use has never done this, is it better to not bring it up. Also wats the name model tool ur using so I can check myself. The block that is.
Guys About .012-.015 is as much as you can move it. We move them if the bore is not in reasonably in the center of the casting.. look at Larry's sheet, it has several moved, and a couple not moved. Tool for checking cylinder wall thickness is an utrasonic thickness gauge, often known as a "sonic checker".. there are many different ones, at different price levels on the market. JW
Ive looked at sonic checkers on amazon. From 100 to 500. Does yours use 2 probes. They dont really specify for engine use.
My Dakota Ultrasonics PR-8(2) also came with one probe. I've seen this unit selling for upwards of $1200.00. With this unit, .... you get what you pay for. Larry
Nice Larry , that would be a the top end of thickness gage. Cast iron being pourus, does that show density?
From what I've seen online, the Dakota PR-82 is kind of the standard for sonic testing a block. The main difference I've read between this tester and the budget units is the lack of a curved probe. Most of the cheap units seem to come with a flat probe that doesn't conform to the curve of a cylinder wall and therefore gives questionable results. I really wish someone would make a unit specifically for engine cylinders that wasn't $1200!
The density of the material is calculated during the calibration step. That step must be performed every time prior to testing the particular item. JW explained to me a while back before I bought my own tester how important this step is because of the differences between block compositions and casting densities. I will periodically re-test the calibration site(s) on blocks during sonic testing just to be sure. Larry
