I thought Clevite made a set of bearing that didn't have full grooves on all the shells.
Number one main only feeds one rod and so does five (if I'm thinking correctly) so they decided to use half groove in those places.
I never do it. I run full groove everywhere. Why King is doing what they are I have no idea. I used Kings on and off since 1995. At times they were almost impossible to get for Chrysler's so I would buy several sets of half groove bearings when I could get them, and then just machine a groove in the bottoms on the lathe.
