OOOw! Something didn't get bored correctly! Before you just replace the bearings I would recomend that at least that rod be checked and cross-checked with a micrometer for roundness. And NO the 20w50
oil did not cause that. Before I went to
synthetic I always ran 20w50 with zero problems even below freezing. A lighter weight may help your starting and so forth but that's about it untill you're well under your 40 deg. BTW, you mentioned stuff in the pan; is the
oil pick-up clean?
Good luck, Steve