Diesel drive installations are equipped with a means of jacking, or barring, over. A great majority of diesel engines are jacked over by hand. One method of rotating the engine is with the use of a turning bar. In this installation, holes are provided around the circumference of the rim for insertion of the turning bar so that the crankshaft can be manually rotated. (See fig. 4-27.) This is a very simple but effective means that allows for the precise positioning of the crankshaft when required for timing.

Figure 4-27.Ring gear and coupling (flywheel).

Still another method of rotating the crankshaft is illustrated in figure 4-28. This engine barring device consists of a pinion and a hex head drive shaft. The drive shaft is mounted in a housing containing an eccentric sleeve arrangement for engaging the pinion with the ring gear on the flywheel.

The barring device shown in figure 4-28 can also be operated by an air (motor) wrench placed over the hex head of the drive shaft. Main drive engines, as well as some auxiliaries, are usually equipped with safety devices that prevent the engine from starting while the jacking gear is engaged. The type of safety devices will depend on the type of starting system used.