procedure varies to some extent, depending on the valveconstruction.Except in emergencies, it is advisable to shut theengine down when troubles cause safety valve popping.Clogged or partially obstructed exhaust ports mayalso cause the cylinder safety valve to lift. This conditionwill not occur often if proper planned maintenanceprocedures are followed. If it does occur, the resultingincrease in cylinder pressure may be enough to causesafety valve popping. Clogged exhaust ports will alsocause overheating of the engine, high exhausttemperatures, and sluggish engine operation.You can prevent clogged cylinder ports by removingcarbon deposits at prescribed intervals. Some enginemanufacturers make special tools for port cleaning.Round wire brushes of the proper size are satisfactoryfor this work You must be careful in cleaning cylinderports to prevent carbon from entering the cylinder-barthe engine to such a position that the piston blocks theport.SYMPTOMS OF ENGINE TROUBLEIn learning to recognize the symptoms that may helplocate the causes of engine trouble, you will find thatexperience is the best teacher. Even though writteninstructions are essential for efficient troubleshooting,the information usually given serves only as a guide. Itis very difficult to describe the sensation that you shouldfeel when checking the temperature of a bearing byhand; the specific color of exhaust smoke when pistonsand rings are worn excessively; and, for some engines,the sound that you will hear if the crankshaftcounterweights come loose. You must actually workwith the equipment to associate a particular symptomwith a particular trouble. Written information, however,can save you a great deal of time and eliminate muchunnecessary work. Written instructions will makedetection of troubles much easier in practical situations.A symptom that indicates that trouble exists may bein the form of an unusual noise or instrument indication,smoke, or excessive consumption or contamination ofthe lube oil, fuel, or water. Figure 3-43 is a general listingof various trouble symptoms that you may encounter.NOISESThe unusual noises that may indicate that troubleexists or is impending may be classified as pounding,knocking, clicking, and rattling. Each type of noise mustbe associated with certain engine parts or systems thatmight be the source of trouble.Pounding or hammering is a mechanical knock (notto be confused with a fuel knock). It may be caused bya loose, excessively worn, or broken engine part. Gen-erally, troubles of this nature will require major repairs.Detonation (knocking) is caused by the presence offuel or lubricating oil in the air charge of the cylindersduring the compression stroke. Excessive pressuresaccompany detonation. If detonation is occurring in oneor more cylinders, stop the engine immediately toprevent possible damage.Clicking noises are generally associated with animproperly functioning valve mechanism or timinggear. If the cylinder or valve mechanism is the source ofmetallic clicking, the trouble may be due to a loose valvestem and guide, insufficient or excessive valve tappetclearances, a loose cam follower or guide, broken valvesprings, or a valve that is stuck open. A clicking in thetiming gear usually indicates that there are somedamaged or broken gear teeth.Rattling noises are generally due to vibration ofloose engine parts. However, an improperly functioningvibration damper, a failed antifriction bearing, or agear-type pump operating without prime are alsopossible sources of rattling noises.When you hear a noise, first make sure it is a troublesymptom. Each diesel engine has a characteristic noiseat any specific speed and load. The noise will changewith a change in speed or load. As an operator, you mustbecome familiar with the normal sounds of the engine.Investigate all abnormal sounds promptly. Knocks thatindicate a trouble may be detected and located by specialinstruments or by the use of a “sounding bar,” such as asolid iron screwdriver or bar.INSTRUMENT INDICATIONSAs an engine operator, you will probably rely moreon the instruments to warn you of impending troublesthan on all the other trouble symptoms combined.Regardless of the type of instrument being used, theindications are of no value if the instrument isinaccurate. Be sure an instrument is accurate andoperating properly before you accept a low or highreading. Test all instruments at specified intervals orwhenever you suspect them of being inaccurate.3-40
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