Brian, the radius is where the bearing surface meets the cast part of the crank. Grinding wheels don't have sharp edges so there is a radius on each end, also the radius keeps cracks from forming.
Since you have one rod cap off, look close at the bearing and how it sets in the cap. You should see its offset to one side, and the cap has a bigger opening that goes over the radius of the crank. You should also see where the bearing was rubbing on one side if this is your problem.
Joe
