Whether a crankshaft is of solid construction (fig. 4-19) or of hollow construction (fig. 4-20), the main journals, the connecting rod journals, and the webs of most shafts have drilled passages for lubricating oil. Two other variations in the interior arrangement of oil passages in crankshafts are shown in figure 4-22. A study of these two

Figure 4-22.Examples of crankshaft oil passage arrangement.

Figure 4-21.Crankshaft with removable counterweights.

oil passage arrangements will give you an idea of the part the crankshaft plays in engine lubrication. In the system illustrated in view A of figure 4-22, each oil passage is drilled through from a main bearing journal to a connecting rod journal. The oil passages are in pairs that crisscross each other in such a way that the two oil holes for each journal are on opposite sides of the journal. These holes are in axial alignment with the oil grooves of the bearing shells when the shells are in place. Since the oil groove in a bearing goes at least halfway around the bearing, a part of the groove will always be aligned with at least one of the holes.

In the oil passage arrangement shown in view B of figure 4-22 (the shaft is shown in fig. 4-19), the passage is drilled straight through the diameter of each main and connecting rod journal. A single diagonal passage is drilled from the outside of a crankshaft web to the center of the next main journal. The diagonal passage connects the oil passages in the two adjoining connecting rod journals and main journals. The outer end of the diagonal passage is plugged.

Lubricating oil under pressure enters the main bearing and is forced through the diagonal passage to lubricate the connecting rod bearing. From there it flows through the drilled con-necting rod to lubricate the piston pin and cool the piston.

In engines that use crankshaft oil passage arrangements such as those just discussed, the connecting rods are drilled to carry the lubricating oil to the piston pins and piston. (Refer to fig. 4-17.) Not all engines have drilled connecting rods. In some V-type engines, drilled passages supply oil to the main and connecting rod bearings, but oil for the lubrication and cooling of the piston assembly may be supplied by centrifugal force or by separate supply lines. Variations in engine lubricating systems are discussed later in chapter 8.