Crankshaft bearings are made of a softer material than the crankshaft journal or cap they sit in. This insures that the bearing material wears before the journal. The crankshafts journal doesn't actually ride on the bearing surface, instead it rides on a thin film of oil between the journal and the bearings.
If the crankshaft journals are worn, scored, or out of round, the gap between the two are affected. Whenever there is contact between the journal and the bearing there will be excessive wear.
Check the bearing for metal particles embedded into its surface. This indicates that two metal parts are in contact with each other creating metal shavings. It's important to find and repair this problem before proceeding. Whenever you find metal shavings in the oil pan or bearings, the oil pump must also be inspected. Look at the backside of the bearing insert for wear indicting that it has spun in its saddle.
Check the main bearing bore for misalignment. There are several methods to do so. Its easiest to use a straight edge and a feeler gauge. Use a blade half the thickness of the maximum clearance. The feeler gauge must not fit between the straightedge and the bores surface. Warpage can be corrected when it isn't too far out of specifications. The block can be line bored and oversized bearings installed.