Mechanical governors used in the Navy are generally of the spring-loaded flyball type. All mechanical governors have a speed droop. This means that as the load is increased at a constant throttle setting, the speed of the engine will drop or droop slightly, rather than remain constant. Consequently, mechanical governors are never used where absolute constant speeds are necessary. There are several types of mechanical gover-nors. Two of the most common types are used on GM 71 engines. One type, known as the constant-speed governor, is used on generator sets and is designed to hold the speed of the engine at a predetermined operating speed. The other type is similar in construction and is used primar-ily for propulsion engines. It has a throttle plate so designed that speeds intermediate between idl-ing and full speeds may be obtained by manual adjustment. The following description applies to both types of governors. Do note, however, that on the constant-speed governor, there is no buf-fer spring adjustment.

In the idling speed range, control is effected by centrifugal force of two sets of flyweights (figure 3-15), large and small, acting against a light

Figure 3-15.GM mechanical governor.

(low speed) spring. Maximum speed control is effected by the action of the high speed (small) flyweights acting against a heavy (high speed) spring. (See figure 3-16.)

Mechanical governor faults usually manifest themselves in speed variations; however, not all speed variations indicate governor faults. When improper speed variations appear do the following:

1. Check the load to be sure that speed changes are not the result of load fluctuations.

2. If the load is found to be steady, check the engine to be sure all cylinders are firing properly.

3. Make sure there is no binding in the gover-nor mechanism or operating linkage between governor and engine, and that no binding exists in the injector control rack shaft or its mounting brackets. If you find no binding anywhere and the governor still fails to control the engine prop-erly, you may assume the governor is worn or unfit for further service until the unit has been completely disassembled, inspected, and rebuilt or replaced.

Figure 3-16.Mechanical governor control mechanism.

Adjustment procedures for the replacement of any governor are listed in the manufacturers instruction manual and should be followed with particular attention given to the precautions listed.