Fig. 20 illustrates a bottom view of a crank case for the L-head motor. It shows the camshaft and crankshaft in position, with the connecting rods mounted on the crank pins. But one camshaft is used, and is driven through helical gears, the accessories are mounted on opposite sides and also driven through helical gears. The crankshaft is of the five-bearing type, while the case is divided on the horizontal center of the crankshaft, all the important parts being carried in this upper half of the case, the lower half serving only as a dust protection, oil splash basin and reservoir.
Fig. 21 illustrates the bottom view of a prominent valve in the head motor, with a three-bearing crankshaft and one camshaft for operating the valves. This crank case differs somewhat from the above in that it is cast in one piece with a separate oil reservoir bolted to it. The timing gears are carried in a housing at the front end of the case, enclosed by a steel cover plate. The magneto is driven from the timing gear housing through flexible couplings in the conventional way. while the pomp is driven through spiral gears front the camshaft.
Fig. 22 shows a sectional view of a two-cylinder opposed motor. This type of motor is mostly used on the light commercial vehicles, and the rase is generally made from cast iron. This case is cast in one piece with circular openings on the ends. through which the crankshaft is inserted. Plates are mounted in these openings and bolted to the case which carries the crankshaft bearings. A large cover plate is used, which carries the camshaft, gears and pushrods. The water pump is driven by the camshaft bevel gears, while the oil pump is driven through an idler gear from the crankshaft.
In some of the two-cylinder motors in use at present the case is divided on the vertical center of the crankshaft and each half is cast integral with a cylinder, while the pushrods and camshafts are also located in the case instead of on the cover plate.
In the two-cylinder opposed type of motor the distance between the crankshaft and the camshaft is generally greater than the distance between the valve and the cylinder centers. This is due to the fact that in this type of motor the camshaft is located at right angles to the cylinder axis, while in the vertical motors it generally makes an angle of 45 to 60 degrees with the cylinder axis. The former case makes it necessary to either place the valve chamber farther from the cylinder axis, thereby increasing the length of the valve passage and consequently the compression space wall area, which is not good practice, or to offset the valves from the camshaft center and to provide the pushrods with an overhanging striker. In Fig. 22 the pushrods are set at an angle to overcome this point, which in this case is easily accomplished, as the valves are carried in the head of the cylinder and operated through a rocker arm.
Fig. 20. Bottom of Crank Case of L-Head Motor.
Fig. 21. Bottom View of Crank Case having Separate Compartment for Oil.
Fig. 22. Sectional View of Two Cylinder Opposed Motor.