When I mock up an engine to degree the cam, check piston/valve clearance, etc., etc., I'll use an old set of mock-up bearings and squirt some
oil on both halves with an
oil can, or rub on some assembly lube before I drop the crank in, and before I put the rods on the crank. You'll be surprised at how much
oil flows out of the bearing and runs down the main cap, or flows out of the rod bearing. I have pulled those bearings back out with wipe marks on them....now mind you they weren't worn, but there was contact....and that was from a low number of revolutions, with no load. If there is no flow, there is no resulting load support.
After everything is cleaned, the crank is polished, and I go to fully assemble with the intended bearings, I will saturate the bearings with assembly lube (I use Royal Purple and it's very viscous), but I'm still shocked at how much squirts out and runs down the main caps when I'm rolling the engine over to do different things.