OPERATING DIFFICULTIES problem of lubrication is one of the most im portant that confronts the Diesel engineer. Many individual engines have achieved a sorry reputation due to poor lubrication facilities or to mediocre grades of lubricating oils. The engineer does well to insist on a high quality of oil, and he should see that the oiling devices function properly. If the lubrication method is incorrect, a proper device should be installed.
Lubrication lubricating systems are at present in general use. The most popular one is the force-feed design where one or more positive-driven mechanical oil pumps force the lubricant to all moving parts with the exception of the crank bearings. These parts are generally oiled by gravity stream lubrication. A design of cylinder oiling that is coming into use employs a spray check valve quite similar to the fuel injection nozzle of a low-pressure engine. This valve, Fig. 174, passes through the cylinder jacket and cylinder wall. The mechanical oil pump is timed to cause the lubricating oil to be injected through this nozzle as the piston is below the central point of its travel. The oil sprays on to the piston, covering a consider able area even though the clearance between the piston and cylinder walls is small. The piston, as it moves upward, swabs this oil over the cylinder walls. This principle of cylinder lubrication is most satisfactory in operation. The oil is deposited when the cylinder temperature is fairly low; con sequently a decided lubricating effect will be experienced before the flame of combustion burns the lubricating oil.
Even when such an injection device is not employed, the oil is always forced into the cylinder by a mechanical oil pump. Although several makes of oil pumps are in use, the majority of domestic Diesels are equipped with the Richardson-Phenix Model M mechanical oil pump. This pump is shown- in Fig. 175, where the course of the oil is indicated by arrows.
An engineer should bear in mind that the mechanical oil pump is subjected to stoppage of one or more oil lines due to the presence of bits of waste. Consequently, as much attention must be given to the pump as to other parts of the engine.
Stream Lubrication.—As has been mentioned, an engine having a mechanical oiler for the cylinders, as a rule, employs either drop or stream lubrication for the bearings. The stream system is preferable since a sufficient amount of oil is assured.
The lubricating oil can be stored in an overhead tank from which piping with sight feeds leads to alI the bearings. The oil, after
performing its mission, flows down into the engine crankcase. Collecting in the case, it is generally led out into a receiver tank or into a filter. Probably the best plan is to have a receiver tank below the engine into which the oil drips can discharge. After the tank contains a half barrel or so, this oil can be pumped, either by motor or by hand, into a filter. After filtering, it can then be pumped back into the overhead tank. If a good filter is purchased, the oil can be reused almost indefinitely. With a filter having ample filtering area, it has been found that the renewal of oil does not exceed ho of 1 per cent. of the oil cir culated. Figure 176 illustrates a well-known filter that is in general use in Diesel plants.
Pressure-feed Lubrication System.—A system for crankshaft and connecting-rod bearings is employed on the Busch-Sulzer. Type B and on the New London Ship and Engine Co. Diesels. This system, as used on the Busch-Sulzer, is outlined in Fig. 177, showing the drilled crankshaft and connect ing-rods, as well as the pump and filtering mechanism. The oil is forced by the pump, which is a rotary geared to the air-com pressor crank disk, into the lower half of the main bearings as indicated. The oil flows around the journal, lubricating the entire surface. The diagonal-drilled passages to the crank pins once each revolution register with the oil inlet opening in the lower bearing shell. • This allows a stream of oil to enter the passage and to flow to the crank-pin box. The connecting-rod also is drilled, and each revolution this passage aligns with the crank end of the diagonal passage,' which causes a supply of oil to pass up the rod to the wrist-pin bearing. The drip from the various parts is caught in the crankcase and from there flows through the filter into the cooler. The pump then draws the oil from the cooler to be reused. In order to seal the various parts of the system, the oil level in the crankcase should be around 3 inches before the engine is started and should always be carried at least 1 inch in depth while the engine is running. The pump discharge has a pressure gage attached; the pressure should aver age around 25 pounds. The gage pressure is a fair indication of the condition of the system. If the pressure shows a decided increase, it is evident that part of the discharge lines are clogged with dirt or waste. If the pres sure drops, usually one or more bearings are worn, allowing the oil to leak out the ends.