In these engines, the oil flow is dedicated to the main bearings first. Then from the mains in the crankshaft, the oil flow goes to the rod bearings and some of that oil squirts to the cylinder walls. At the same time through another main bearing oil galley feeds the camshaft bearings and then the tappets. The oil filter is fed last from the tappet oil galley. Think of it like a garden hose that feeds a lawn sprinkler. The main hose feeds the first lawn sprinkler (main bearings and rod bearings), then goes to the next sprinkler(camshaft bearings and tappets), the next sprinkler has a much smaller feed hose ( a restricted flow) from the second sprinkler in line ( feeds the oil filter and oil pressure gauge). The pressure drops to a degree depending on how many sprinklers you have, but the pressure is still greatest at the first sprinkler (main bearings and rod bearings.) The oil does not flow from the pump to the oil filter at the same time it flows to the mains and rods. The oil flow is not split into separate channels, but goes to the 4 main bearings at the same time. Actually oil returns (leaks) to the crankcase from each of the lubricated parts inside the engine including but not limited to the mains, rods, camshaft bearings and tappets. The largest leak will cause the greatest pressure loss. The pressure loss from the oil filter is always the same because of the line size and the filter medium, and does not cause a loss in oil pressure as the engine wears. If the filter element gets plugged, there will be no oil pressure loss from the filter. These are only partial flow filters. I hope this helps.
