As Don and Tech both noted, pressure in an oiling system for rotating machinery is not as important as the availability of a ready and constant supply of lubricant. Once a crankshaft, or any rotating piece of machinery is moving, supported on an adequate film, surface tension and film shear take over, and as long as there is lube available, the rotation will pull it into the space between the bearing and the shaft. A good example of this is large rotating machines like really big motors and generators: most have external auxiliary oil pumps that are capable of rather high pressures. The pumps are started before the shaft is turned, so as to pump high pressure oil into the bearing space and "lift" the shaft off of the bearing surface, then the machine is started. After the machine reaches it's operating speed, the oil pumps are turned off, and slingers or dippers pick up oil from the plenum, or reservoir beneath the bearing and deposit it around the bearing edges where it is drawn into the clearanced space and provides a ready cushion of oil for the shaft to rotate on. Some of the machines I used to work on had armatures that weighed over 100K lbs, and they worked just fine in this fashion. In a reciprocating engine, the power pulse is in a tangent direction to the rotation of the crankshaft, but it is quickly converted to rotational force, and is not a significant factor, especially in multi-cylinder engines; the more cylinders, the more the pulses will be distributed around the rotational axis of the shaft. That is why a V8 is smoother than a straight six, and a V12 even smoother.