The old school method (pre-Plastigauge) was to insert a small piece of shim stock between the bearing and the crankshaft, torque the cap, and see if the crankshaft could be turned. For instance, if I wanted a .002" rod bearing clearance, I'd insert a piece of .002" shim stock about 1/8" wide under the bearing, and add or remove shims until I could turn the crankshaft with a firm drag, not quite locked up. Precision-insert bearings that don't use shims can be checked the same way, but you'll need a good selection of shim stock thicknesses!
Jerry
