Oil System Description
Oil Supply Circuit
Oil flow is controlled by a needle valve located in the oil supply tank. As oil exits the tank the flow is verified by observation using the sight glass. The oil should be a solid stream.
Oil travels from the sight glass through the soft copper tube to the 90 deg fitting located on the pressure side transfer tube.
The oil travels through the transfer tube and enters the gear pressure pump. The pressure is is raised to between 75 and 100 PSI. Under pressure, the oil is forced into a circular groove machined into the rear crankshaft journal. The groove leads to a drilled hole in the crankshaft. Because of the groove, oil can enter the crankshaft from any crankshaft position.
The minor oil leakage from the main shaft and oil pump shafts is allowed to collect in the bottom at the rear of the crankcase. This leakage is contained by the oil separator plate. This plate has a lip seal and outer " O " ring to prevent the oil from entering the intake space. From here, the oil drains to the center section of the crankcase by way of two holes drilled in the main bearing and corresponding rear crankcase rail.
The remaining oil flow travels forward through the first of the crankshaft's two 45 deg oil galleries. This passage leads to the crankshaft master rod journal. Some of the oil leaks from the journal and, because of the crank rotation, sprays oil to lubricate the cylinder walls, the bottom of the pistons and the piston wrist pins. This oil carries away a considerable amount of heat that has not been rejected to the air by the cylinder and cylinder head cooling fins.
The remaining oil travels forward along the second crankshaft 45 deg oil gallery to the front main bearing. Oil lubricates the front main bearing, then flows to lubricate the tongue and groove feature supporting the moving cam ring.
Because the cam is spinning, oil travels outward through two relief grooves and lubricates the cam lobes, valve tappets and valve tappet bushings. This oil flow also lubricates the cam reduction gear. An oil mist lubricates the front ball bearing.
Oil Return Circuit
The oil that lubricated the front main bearing, cam and cam reduction gearing in front of the engine moves rearward through an oil hole in the bottom of the front main bearing and a corresponding hole in the front crankcase support rail.
This oil from the front of the engine joins the oil returning from the master rod journal and cylinders. Because the cylinder barrels extend beyond the inside diameter of the crankcase, there is sufficient room for the oil to collect between cylinders 5 and 6 before draining to the sump by way of the front oil sump tube.
The rear oil sump tube extends to the bottom of the sump tank, allowing the oil to be drawn upward through the oil scavenge passages to the oil scavenge pump. The scavenge pump has a capacity of 2 1/2 times the pressure pump, ensuring all of the oil is removed from the sump.
Pushed along by the scavenge pump, oil travels through the scavenge transfer tube and 90 deg fitting. Oil in the soft copper scavenge line is exposed to the prop air blast. This allows the heated oil to cool as it is being returned to the tank.
Once in the tank, there is a sufficient amount of oil to allow the entrapped air to separate from the oil and vent through the tank fill cap vent.
The combustion gas that leaks past the piston rings would soon pressurize the crankcase and force oil to escape from the front cover and various valve tappets.
The center of the front crankshaft is drilled, allowing the combustion gas to be vented while preventing the oil from escaping. The prop retaining nut has a similar set of vent holes to allow the gas to escape.