Figure 8-9 illustrates a typical lubricating oil system in a General Motors series 71 in-line diesel engine. Refer to figure 8-9 as you trace the flow of oil through this type of lubricating oil system. (Note the directional arrows as we continue our discussion.)

Flow of Lubricating Oil

The lubricating oil is circulated by a gear-type pump mounted on the No. 1 and No. 2 main bearing caps. The pump is gear driven by the crankshaft. All the oil leaving the pump is forced through the full-flow oil filter to the cooler and then into the oil gallery in the cylinder block. From the oil gallery, the oil is distributed to the various engine bearings. Note that the drains from the cylinder head and other engine parts lead back to the oil pan.

When the pressure in the engine oil gallery exceeds approximately 100 psi, a spring-loaded integral plunger relief valve (A), located in the oil pump body, bypasses excess oil from the discharge to the inlet side of the pump. If the oil cooler should become clogged, the oil will flow from the pump through a spring-loaded bypass valve (B) directly into the oil gallery.

Clean engine oil is assured at all times by the use of a replaceable element type of full-flow oil filter that is incorporated in the lubricating oil system. This filter is installed between the pump and the cooler, and it filters all the lubricating oil before it enters the engine. As mentioned before, there are two conditions under which oil will NOT pass directly through the filtering elements to the engine: (1) when the oil is cold (high viscosity), and (2) when the filters are clogged. When one of these conditions exists, a bypass valve (C) opens and the filter elements are bypassed.

A regulator (relief) valve (D) that is located between the pump outlet and the inlet to the cylinder block works to maintain stabilized lubricating oil pressure within the engine when the engine is operating at all speeds. This valve stabilizes the lubricating oil flow rate regardless of the temperature of the oil. When the oil pressure at the regulator valve exceeds 45 psi, the valve opens and remains open until the pressure falls below the operating pressure.

As a optional feature, a bypass type of filter (E) with a replaceable element may also be used. In this design, a portion of the lubricating oil is continually bypassed through the filter. The filtered oil is then returned to the engine oil pan.

Distribution of Lubricating Oil

Oil from the cooler is directed by a vertical passage to the main gallery of the cylinder block. (Refer to fig. 8-9 and the directional arrows.) As shown in figure 8-9, this gallery distributes the oil to the main bearings and to a horizontal passage at each end of the cylinder block. From each of these two horizontal passages, oil flows to the end bearings of the camshaft and balancer shaft. In addition, oil is forced through an oil passage in the camshaft which lubricates the camshaft intermediate bearings. Oil to lubricate the connecting rod bearings and piston pins, and to cool the piston head, is provided through the drilled crankshaft from the adjacent main bearings. The gear train is lubricated by the overflow of oil from the camshaft pocket. The blower drive gear bearing is lubricated through an external pipe from the rear horizontal oil passage of the cylinder block.

Valve and injector operating mechanisms are lubricated from a longitudinal oil passage on the camshaft side of the cylinder block which connects to the main oil gallery. Oil from this passage enters the drilled rocker arm shafts through the lower end of the rocker shaft bolts and rocker shaft brackets. Excess oil from the rocker arms lubricates the exhaust valves and cam followers.