Figure 4-1.—GM mechanical governor.control is effected by the action of the high-speed(small) flyweights acting against a heavy (high-speed)spring. See figure 4-2. If you have any questions or needmore illustrations to understand the concept of governoroperations, refer to chapter 9of Engineman 3,NAVEDTRA 10539.Mechanical governor faults are usually revealed inspeed variations. But not all speed variations are faultsof the governor. When abnormal speed variationsappear, you should first do the following procedures:1. Check the load to be sure the speed changes arenot the result of load fluctuations.2. If the load is steady, check the engine to makesure all the cylinders are firing properly.3. Make sure there is no binding in the governormechanism or operating linkage between the governorand the engine. There should be no binding in theinjector control rack shaft or its mounting brackets. Ifyou find no binding anywhere and the governor still failsFigure 4-2.—Mechanical governor control mechanism.to control the engine properly, you may assume that thegovernor is worn or inoperative.If the governor is the cause of improper speedvariations, it must be completely disassembled,inspected, and rebuilt or replaced. When it is necessaryto disassemble and reassemble the governor, you shouldsecure a copy of the manufacturer’s instruction book andfollow the instructions given. During reassembly of thegovernor, use only hard grease on the gasket! Under NOcircumstances should you use shellac on the gasket.Adjustment procedures for the replacement of anygovernor are listed in the manufacturer’s instructionmanual and should be followed with particular attentiongiven to the precautions listed.OVERSPEED SAFETY DEVICESMechanical overspeed trips depend upon thecentrifugal forces developed by the engine and must bemaintained in good working condition. A faultyoverspeed device can endanger not only the engine butalso the personnel. The engine could explode or fly apartbecause of the uncontrolled speed.The engine instruction manual contains informationas to the speed at which the overspeed device is designedto function. Most overspeed trips are adjustable. Beforemaking any changes in the adjustment of the overspeedtrip, you must determine the cause. If the engine did nottrip out, was it for some reason other than the action ofthe element of the overspeed trip? You should firstcheck the accuracy of the tachometer and then test the4-3
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