Too difficult?
All auto engines have "pressurized oil systems".
The highest, most important pressure is developed at the bearing/journal interface as the result of journal rotation.
Modern engines have a pump which delivers oil under pressure to replace what leaks from the bearing clearances, but the delivery pressure is only a small fraction of what is present in the bearing.
The pre-54 L6 has oil pressure to the main bearings, but relies on a pressure stream (not constrained by a tube or passage) to supply the rod bearings which then develop the actual operating pressure exactly as usual: by rotation.
Both systems fail if the supply method's (pump or stream) delivery rate is slower than the oil escapes from the clearance.