needle valve even though it has previously beendone at the factory or repair facility. This adjust-ment must be made with the governor installedand controlling an engine with a load. If this isnot done, high overspeeds and low underspeedsafter load changes will result and the return tonormal speeds will be slowed. Maintenance andrepair of each unit must be in accordance withthe manufacturer’s maintenance manual and thePMS.NOTE: When governor troubles aresuspected, before performing any maintenance oradjustments, always disconnect the governor fuelrod end from the fuel control rack and ensure thatthere is no sticking or binding of the rack. Thisprocedure is necessary to determine if the trou-ble is actually in the governor.The chart in table 3-1 lists some of theprobable causes of trouble which are common tomost hydraulic governors. This chart should beused for training purposes only; it must NOT beused to troubleshoot a governor. Always use theapplicable manufacturer’s instruction manual fortroubleshooting. Following are the definitions ofthe terms used in the chart.HUNT: A rhythmic variation of speed whichcan be eliminated by blocking the fuel linkagemanually, but which will reappear when returnedto governor control.SURGE: A rhythmic variation of speed alwaysof large magnitude which can be eliminated byblocking the fuel linkage and which will not reap-pear when returned to governor control unless thespeed adjustment of the load changes.JIGGLE: A high frequency vibration of thegovernor fuel rod end or engine linkage. Do notconfuse jiggle with normal regulating action ofthe governor.Mechanical GovernorsMechanical governors used in the Navy aregenerally of the spring-loaded flyball type. Allmechanical governors have a speed droop. Thismeans that as the load is increased at a constantthrottle setting, the speed of the engine will dropor droop slightly, rather than remain constant.Consequently, mechanical governors are neverused where absolute constant speeds are necessary.There are several types of mechanical gover-nors. Two of the most common types are usedon GM 71 engines. One type, known as theconstant-speed governor, is used on generator setsand is designed to hold the speed of the engineat a predetermined operating speed. The othertype is similar in construction and is used primar-ily for propulsion engines. It has a throttle plateso designed that speeds intermediate between idl-ing and full speeds may be obtained by manualadjustment. The following description applies toboth types of governors. Do note, however, thaton the constant-speed governor, there is no buf-fer spring adjustment.In the idling speed range, control is effectedby centrifugal force of two sets of flyweights(figure 3-15), large and small, acting against a lightChapter 3—ENGINE MAINTENANCE121.22Figure 3-15.—GM mechanical governor.3-23
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