All About Engines

The Modern Reciprocating Engine i*5 in the same straight line, fairly close together, as in at the opposite ends with bearings close up to them, as in Fig. 66, the vibration will generally be small. But if they are some dis- tance apart, to some extent each end of the shaft will be alternately pushed and If the two cranks are Fig. 65, or if they are Fig. 65.—Crank for double« cylinder engine pulled, and there will be a tendency to twist the whole engine first in one direction and then in the other. Fig. 66.—Crank for double-cylinder engine So, however far apart the cranks, it is necessary in high- speed two-cylinder engines to employ balance weights on each crank. More- Fig. 67.—Two cranks at right angles over, the bearings should be as close up to the cranks as possible in order to avoid the shaft being bent. As a matter of fact, double-cylinder engines are not always made with the cranks in opposite directions. Both cranks would then be on their dead centres at the same time, and there would be occasions upon which the engine would not start without assist- ance. The cranks, therefore, are more frequently set at right angles to one another (Fig. 67), because one of them is sure to be in the correct posi-