The problem with 216's with a little wear is that the oil pressure gets so low that the upper end parts don't get lubed. Every time the oil lubricates a part such as a main bearing, cam bearing, etc., a little oil leaks away. That leaves a bit less volume to lube subsequent parts down the line. There needs to be sufficient volume to get to the end of the line, so to speak. Oil pressure builds up when there's more volume than the bearings and other pressure-lubed parts require. It's theoretically possible to get adequate lubrication with zero oil pressure, as long as the last item in the circuit receives enough oil, just as the pressure disappears. In practical terms, a minimum pressure of 20 PSI or a little more is needed with the engine at normal operating temperature to assure there's enough reserve volume for consistent lubrication of all the parts. Most tired 216's can't manage that feat, and a little more pump volume will remedy the problem. All oil pumps that I'm aware of have relief valves- - - -they're there to prevent mechanical damage when the oil is cold and thick.
A bit of trivia- - - -when the small block Chevy V8's started getting enough miles on them to need overhauling in the late 1950's, a "normal" in-the-frame overhaul consisting of rings, rod bearings, and a valve job didn't work well- - - -the oil pressure warning light would flicker at hot idle, particularly on automatic transmission cars. That pressure light switch turned on at 7 PSI. The culprit was excessive oil leakage at the cam bearings, resulting in idle oil pressure low enough to trigger the low pressure light. Dad stopped doing in the frame rebuilds after that because high-volume oil pumps for small block V8 engines hadn't been invented yet. That happened about 20 years later!
Jerry
