Edit: Dirtybee typed faster than me...

The 'radius interference' is where the edge of the bearing binds on the crank.

If you look at an original crankshaft, there are sharp corners at the edges of of the journals. Most aftermarket cranks have a fillet radius at each end of the journal. This one simple detail makes the crank stronger, even with everything else being equal.

If the radius at the corner of the journal is too big, it can rub on the end of the bearing.

This is something that needs to always be checked on every build with an aftermarket crank - even if you run a narrow bearing (Clevite among others offers narrower bearings to give more clearance for exactly this situation).

FWIW, the Source had (has?) issues with the corner radii being so large that even the narrow bearings (like Clevite "HN") won't clear w/o cutting a little on the edge of the bearing. Just like shown in BG's picture.

Another issue to look for is taper on the journal, where one side is slightly larger than the other. This has nothing to do w/ the fillets in the corners, but should also be looked for on any aftermarket crank (especially a brand new one - you'd catch a funny looking bearing wear pattern on a rebuild).

My 4.25" "B" crank from 440 Source had .0015" taper on all 5 mains; the crank snout was off .001", the rod journals were straight, but the radii were so large I had to make some pretty heavy cuts on Clevite HN (narrow) bearings.

My crankshaft was a lightweight piece with the pendulum-cut counterweights (extra material removed from counterweights near centerline of the crank) and scalloped crank flange. Looked fairly well finished for an inexpensive part.

-Bill