Fig. 27 illustrates a sectional view of a full force feed system of lubrication which is built into the motor. Oil is carried in a reservoir bolted to the crank case and is circulated by a gear pump mounted at the rear end of the case driven from the cam shaft. The pump forces oil up through a pipe over the main bearings and is provided with a pressure relief valve. This distributing pipe has blanches which communicate with the main bearings and the timing gears. From the main bearings the oil is forced through a hollow crank shaft to the connecting rod bearings. These connecting rods have tubes inserted in them so that the oil can be forced up to the piston pin bearings. Cam shaft bearings are lubricated by means of passages connected with the system. A certain portion of the oil works out from the connecting rod bearings, is thrown off as the crank shaft revolves and forms a fine spray which lubricates the cylinders, pistons and interior parts of the motor. An indicator which shows at all times the level of oil in the reservoir is placed adjoining the combination breather and filling tube. The oil pump and its strainers are removable from the lower half of the crank ease without disturbing other parts. The pressure relief valve permits a certain oil pressure on the bearings. Should the pressure exceed this predetermined amount the relief valve will open, permitting the excess oil to return to the reservoir. Oil which overflows and accumulates in the case flows into a trough into which the connecting rods dip. This trough has holes on one side which allow the oil to drain back to the reservoir beneath so that a constant level of oil is maintained.
Fig. 28 illustrates the Mack oiling system which is a combination of the gravity and force feed type. Oil is pumped from the reservoir at the bottom of the crank to a tank cast integral with the front pair of cylinders. This tank is provided with a filter and an overlow which leads to the timing gear housing. This tank serves two functions: first, to heat the oil while the engine is cold so that the oil will flow freely and second, to cool the oil when the engine is working hardest, as the oil may reach a temperature of 390 degrees Fahrenheit, while the cooling system seldom reaches a temperature higher than 190 degrees Fahrenheit. From the tank the oil flows to a main header which supplies oil to the main bearings and through a second header which supplies oil to the troughs into which the connecting rods dip. A pressure gauge is used to indicate the oil pressure and the pump is provided with a strainer to filter the oil before it is recirculated.
The constant level splash and force feed systems are the most popular, and as positive driven pumps are resorted to, to feed the oil, the general tendency is to provide oil leads of a large diameter and to reduce the number of bends to a minimum. Whenever bends are necessary they should be made as large as possible to reduce the obstructions and resistance.
From the above it can readily be understood that the writer considers the constant level splash recirculating system the simplest in use at present. Its operation is mechanical and the attention required is reduced to a minimum, while at the same time it is quite economical on oil.
The advantages of the force feed system are that the oil may be forced to the bearings under separate pressure, reducing the danger of the oil being forced out by the bearing pressure. It is generally agreed that with force-feed the specific pressure on the bearing can be increased and that the bearing will last longer, while on the other hand the writer finds that this system is more expensive to install and less economical of oil. It would appear to be better adapted to commercial car engines which operate at or near their full load for a considerable length of time.
In the gravity feed system the oil leads must be carried on the outside of the motor, which presents some complications, as they will require attention at intervals. The economy is possibly on a par with the constant level splash system. Mechanical oilers are very rarely used on the types of commercial cars, being practically obsolete.
Fig. 27. Full Force Feed Lubricating System.
Fig. 28. Mack Oiling System - Combination Gravity and Force Feed.