There will be the disadvantage, however, that the pistons, moving up and down together, will cause vibration, which in the course of time will be likely to give trouble. To overcome this, a 2-cylinder engine can be built as indicated in [Figure 4].
In this engine the cranks project on opposite sides of the crank shaft instead of on the same side, as in [Figure 3]; the pistons thus move in opposite directions, and produce no vibration. Power will be unevenly applied, however, for both power strokes occur in one revolution, with two dead strokes in the succeeding revolution.
Fig. 4.—2-Cylinder Power Diagram, 180 Shaft
With piston 1 moving down on power, piston 2, moving upward, can only be performing compression or exhaust. If it is on compression, its power stroke will follow the power stroke of piston 1, while if it is on exhaust its power stroke will have occurred immediately before the power stroke of piston 1. In either case one power stroke follows the other, taking place in one revolution of the crank shaft, while in the following revolution both pistons will be performing dead strokes.
While there is no vibration from the movement of the pistons in this engine, the uneven production of power will produce vibration of another kind.
These two types may be built with the cylinders standing up or lying down; that is, they may be either vertical engines or horizontal engines. The double opposed engine, which is built only in horizontal form, is free from either kind of vibration, but has the disadvantage of occupying more room than the others. The cylinders, instead of being side by side, and on the same side of the crank shaft, are placed end to end, with the crank shaft between them, as shown in [Figure 5].
The pistons make their inward and outward strokes together, but in so doing they move in opposite directions. Thus every power stroke is followed by a dead stroke, as in the engine shown in [Figure 3], while the movement of one piston balances that of the other, as is the case with the engine shown in [Figure 4].
