Alignment The gear train is in alignment when the gear and the pinion are parallel. That is, the axis of the two shafts are in the same plane and equal distance from each other at

Figure 3-2.- Progressive destructive pitting.

Figure 3-3.- Cracked teeth

Figure 3-4.- Broken tooth.

all points. In service, the best indication of good alignment is good tooth contact.

The technical manual furnished with each gear installation describes the procedures for determining the proper depth of mesh and parallelism of gear and pinion shafts. The length of tooth contact across the face of the gear teeth is the key to satisfactory alignment of reduction gears.

Poor alignment between the line shaft and the MRG may be detected at the reduction gear. Uneven loading of the low-speed gear train and noisy operation in certain speed ranges are two common results of poor line shaft to MRG alignment.

The most favorable alignment position of the main engine to the reduction gear is when they are concentric at full power at the proper operating temperature. The flexible high-speed coupling is designed to handle the transient condition of slight misalignments as the machinery comes up to temperature. The two most common forms of misalignment between the prime mover and the driven shafts are angular and parallel offset, as shown in figure 3-5.

The object of the alignment is to locate the turbine so the axis of the spindle will be concentric with and parallel to the axis of the reduction gear input pinion shaft. Attaining alignment is complicated by the fact that the turbine, reduction gear, and foundations all

Figure 3-5.- Angular and parallel misalignment.

expand as they are heated during operation to the hot running conition. Another factor is when operating pinion shafts move higher in their bearings under the influence of the hydrodynamic oil film and tooth pressure. These changes in position have been predetermined by the manufacturer, and you can find the offset readings in the appropriate technical manual for the installation.