Thread: Dial Bore Cylinder Question

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Been experimenting with some Telescopic Gauges and a dial bore gauge thanks to Denny. Assuming I've been doing things right, my dial bore gauge taper measurements from top, middle, bottom of each cylinder looked pretty good and i inputted the readings into an excel file. Although i don't have the file in front of me (can post later), I don't recall seeing any taper variance beyond 0.0005. From what I've gathered so far, it appears that the dial bore gauge appears more accurate or at least is much quicker. I've noticed with the telescopic gauge, it seems to require a little more patience and finess with your hands when you go to lock it down before taking it out of cylinder. Nonetheless, both tools are in in-experienced/or a new learner's hands (me). Anyhoo, i got to thinking and my curiosity has got me wanting to ask a question. A lot of my cylinder measurements (on a 4.030 motor/355) come out to around 4.033 or 4.032. If i do the math that shows a difference of .003 or .002 from a true 4.030. I've heard machinists, when they bore, like to be within .0001. Anyhow, i was just curious if a guy was measuring the size of a cylinder how much of a difference from what it should be to what he measured it at, before its rebore time? .005-.007? Example, assume a 4.030 measured 4.0330 both ways from top, middle, and bottom of cylinder. That would be Zero variance at all levels but the cylinder as a whole would be .003 oversized. In my estimation that appears very reasonable, but what is the max before a rebore is needed?

When you are thatclose on the specs-the cylinder wall surface finish is probably more important than that little bit of clearance-
Most chevy bores are stated at .001 over the nominal size------4.001, 4.021, 4.031--------

You need to mearsure the pistons to determine there sizes before worrying what the cylinder size is. Also, if you don't have a dial bore setting guage--use the same mike to measure the piston that you use to measure/set the dial bore guage------

and also the use of a torque plate will change/alter the cylinder shape the same as if a head was torqued in place and this is reason race engine builders will use torque plates and temperture conttrol to get the most accurrate results