Oil clearances- - - -the amount of space between rotating parts and the bearings they run in. For instance, a connecting rod might have a clearance tolerance of .0005" to .003". The bigger the clearance, the more oil flow is required to keep the space filled with oil. The only reason oil pressure builds up at all is that the oil pump is supplying more oil than the bearings need for lubrication. If one drop of oil is supplied to a bearing every time a drop leaks out, the oil pressure would be zero, yet the bearing would get adequate lubrication because it's never allowed to run out of oil. The pressure relief valve is there to prevent a very efficient oil pump from developing a hydraulic lock and breaking the drive gear or the pump shaft. A solid stack of oil can't be compressed- - - -the engine will stall or something's going to break. The tension of the relief spring determines what the maximum pressure is supposed to be, not the capacity of the pump to develop it.
A 216 engine does not have oil pressure supplied directly to the connecting rods- - - -a stream of oil is sprayed across the oil pan in line with each connecting rod, and the dipper on the rod intersects the stream just as the rod reverses direction at the bottom of the stroke when load on the bearing is at a minimum, and a little oil gets forced into the gap between the rod and the crankshaft. The faster the crankshaft is turning, the more oil gets into the gap. At idle with very slow rod speed and low oil flow from the squirters, a trough below the rod gets filled with oil and the rods get lubed by dragging the dippers through the oil-filled trough.
The trick is to supply ALL the bearings with enough oil, as each time a little oil leaks out of a bearing and drops back into the oil pan, less pressure is available to push the rest of the oil down the line to the next place that needs lubrication. The critical parts that get pressure lubrication in most engines are the cam bearings, the main bearings, the rod bearings, and the valve system such as rocker arms, pushrods, etc. The other parts get lubed by "splash", the oil that gets thrown off the crankshaft, connecting rods, and other rotating parts. If you get the bearing clearances right, you should have plenty of oil pressure, even if the pump is slightly loose on clearance. It all works as a system- - - -just working on the pump won't give you good oil pressure.
Jerry
