If adjusting clearance on poured-bearing rods was as difficult as we've been led to believe, none of the stovebolt engines would have survived long enough for any of us to have the opportunity to work on them. Just about anybody with more than three brain cells to rub together can do an acceptable job of adjusting rods- - - -he just has to pay attention to detail and be willing to invest some serious time on a creeper or under a lift.
The usual oil clearance range on babbit-pounder rods is from .001" to .003". The closer you get to minimum, the less often you'll have to go back in and readjust things. Yes, it helps if the crankshaft journal is reasonably round and smooth. Nothing chews up Babbit quicker than a rough, out-of-round connecting rod journal. Lots of rod journals have been smoothed out with a piece of cloth-backed fine-grit sandpaper and some "shoeshine" motion, however. It's possible to get a pretty good idea if the shaft is round enough to proceed by taking some measurements with a dial caliper, and most folks who don't do machine work routinely have better luck getting an accurate reading with one of those tools than with a micrometer. No, it's not as accurate, but it will be close enough to get a ballpark figure whether the shaft is round enough to proceed. A reasonably accurate dial caliper can be has for less than 40 dollars online or from a place like Harbor Freight or Northern Tool. Most of the wear on a rod journal happens from top to bottom as the piston/rod assembly reaches its upper or lower limit of travel and changes direction. I believe the maximum "out of-round" allowable is in the neighborhood of .002", but the closer to perfectly round it is, the better. Ditto on "smooth"- - -a mirror-polish would be nice, but I've run many miles with crankshafts that had some noticeable pits. High spots are another matter altogether, so smooth them out as much as possible.
Once the shaft is determined to be reasonably round and smooth, and the surface of the soft metal in the rod isn't badly deteriorated, remove a shim or two until the crankshaft has a noticeable drag when the rod bolts are tightened and the flywheel is turned by hand. Reinstall shims until the drag is barely noticeable. I like to put a small piece of .0015" brass shim stock between the rod cap and the crankshaft, and remove shims until I get a firm drag, then remove the spacer and reassemble and torque the rod. I've had better results using this method than I do with Plastigauge.
My Motor manual says it's possible to compensate for up to .004" of bearing and/or crankshaft wear by removing shims. Just use a little common sense and don't get the rods too tight. I'd rather run with rods that have .0025" of clearance and rattle a little, than with .001" clearance and too much drag.
Jerry
