Chapter 3—ENGINE MAINTENANCEThis is impossible if backlash, looseness, or playexists in the control system. Continuous or inter-mittent movement of the rack may indicate ex-cessive looseness. Engine speed variations are alsoindicative of this problem. Note that even thoughthese symptoms are characteristic of a loose rack,a governor which is dirty or out of adjustmentwill present similar symptoms.Backlash in a fuel control system is generallydue to a wornout gear, rack, or control sleeve.When you disassemble a pump or injector foroverhaul be sure to inspect all parts of the con-trol system for signs of excessive wear. If the rackmay be moved more than a prescribed amountwithout moving the plunger, find the parts thatare worn, and replace them.Improper CalibrationWhen improper calibration (balance) of fuelinjector pumps or injectors occurs, there is a dif-ference in the amount of fuel injected into eachof the cylinders. If some pumps or injectorsdeliver more fuel per stroke than others, theengine will be UNBALANCED; that is, somecylinders will carry a greater load than others. Thiscondition may be detected by differences incylinder exhaust temperatures and firingpressures, and by smoky exhaust from theoverloaded cylinders. Roughness in operation andengine vibration are also indicators of anunbalanced condition.It is important to remember that many othertypes of engine difficulties may cause enginesymptoms identical with those due to unbalance.So when unbalance is suspected, consider first afew of the other faults that may be present suchas poor condition of piston rings, inaccurateexhaust pyrometers and thermocouples, mistimedor faulty engine exhaust or inlet valves.Improper TimingImproper timing of a fuel system will resultin uneven operation or vibration of the engine.Early timing may cause the engine to detonate andlose power. Cylinders which are timed early mayshow low exhaust temperatures. Late timingusually causes overheating, high exhausttemperatures, loss of power, and smoky exhaust.Although, usually, improper fuel injectiontiming is caused by failure to follow the manufac-turer’s instructions for timing, there may be othercauses for the difficulty, depending upon designof the particular systems. For example, fuelinjection time in the injection pump of a Boschsystem may get out of time because of a wornpump camshaft. The same problem may occurwhen the adjusting screw on the injector controlrack of a GM system becomes loose. Either ofthese conditions will change fuel injection timing.Faulty calibration and improper timing aregenerally due to failure to follow instructionsgiven in the engine technical manual and the fuelinjection equipment maintenance manual. Thesemanuals should always be consulted and fol-lowed whenever timing or calibration difficultiesarise.GOVERNORSTo control an engine means to keep it run-ning at a desired speed, either in accordance with,or regardless of, the changes in the load carriedby the engine. The degree of control requireddepends on two factors: The engine’s performancecharacteristics and the type of load which it drives.In diesel engines the speed and power output ofthe engine is determined by varying the amountof fuel that is injected into the cylinders to con-trol combustion. There are two principal types ofgovernors: hydraulic and mechanical.Hydraulic GovernorsIt is beyond the scope of this training manualto list all of the possible troubles which may beencountered with a hydraulic governor. This sec-tion deals only with the most common ones. Poorregulation of speed may be due to the faulty ad-justment of the governor or to faulty action ofan engine, a generator, a synchronizing motor,a voltage regulator, or any piece of equipmentwhich has a direct bearing on the operation of theengine.Manufacturers state that 50% of all governortroubles are caused by dirty oil. For this reason,3-21
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