obviously if you kept on driving it with big ends knocking you would fuck your crank up. what i'm saying is, if the crank surfaces look ok (no noticable grooves) then there is a chance that your shells had just worn out and you would get away with new shells, but if the crank journals are scored then the only course of action is a regrind which unfortunatly means an engine out job. so if it were me and the crank looked ok i would gamble on some new shells.