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Gun loading system hydraulic machinery uses hydraulic pressure to position mechanical devices that move rounds of ammunition through the system for firing. Almost without exception, these mechanical devices must be adjusted to maintain travel and proximity tolerances to ensure proper performance. Some adjustments are verified during routine maintenance as part of the procedure contained on an MRC. Most often, however, you will need to make adjustments to mechanical equipment after it has been disassembled, repaired, and reassembled. Such is the case, for example, after a linkage has been removed to get to a hydraulic packing that required replacement or after a damaged component has been removed and replaced You must refer to the system maintenance manual to determine the exact procedure and tolerances before making any mechanical adjustments. With this in mind, we will now provide you with some general information on the different types of mechanical adjustments found on gun mounts.


The most common mechanical adjustment involves a threaded linkage that is screwed into or out of another component to adjust its travel or proximity to other components. Most mechanical linkages are connected to each other and to the components they control or operate with a clevis (fig. 12-11). A clevis is a U-shaped piece of metal with holes through the ends where a pin is inserted to attach one thing to another. The clevis is used as a flexible connection for mechanical linkages. It can be adjustable or nonadjustable and is often refereed to as a yoke. The adjustable clevis may be either threaded through the base to allow for the insertion of a threaded shaft or it can be manufactured to include a threaded shaft. Often, the two configurations are used together as opposite ends of an adjustable linkage.

Threaded Shaft

Another common mechanical adjustment consists of an operating shaft threaded in one or both ends. A connecting shaft or actuator is screwed in or out of these threaded ends to adjust its travel or proximity to another component. This configuration can be used to adjust cam followers and mechanical actuators that push or pull a component to cause its operation (fig. 12-12).

Figure 12-11.-The clevis.

Figure 12-12.-Threaded linkage adjustments.

Figure 12-13.-Eccentric shaft.

Eccentric Shaft

In some special instances a mechanical adjustment may involve shifting the rotational axis of a pivoting component. This is accomplished through the use of an eccentric shaft. An eccentric shaft, as shown in figure 12-13, is an otherwise straight shaft with an offset disk in the middle. The offset disk is the rotational axis of a pivoting component. Being offset, it allows this axis to be adjusted simply by rotating the shaft. In some cases, the eccentric shaft may be used as an adjustable securing pin instead of a pivot point.


Some gun mount adjustments are accomplished using shims. This is often the case when a major component is replaced and must be "fitted into alignment or proximity with surrounding components. A shim is a noncompressible material, in sheet form, that is inserted between two components that are bolted together. Shim material is available in a standard pack of three different dimensions that can be cut and added together to achieve the desired thickness.

Hydraulic and mechanical maintenance is at the core of the traditional work of the Gunner's Mate. Mastery of hydraulic and mechanical maintenance, along with proficiency in troubleshooting electronic control circuits (chapter 5), is the defining characteristics of your expertise as a Gunner's Mate.

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