Figure 3-35.—Crankshaft bridge gauge.leave an impression in the soft bearing metal becausethe gauge material is softer than the bearing. To use thismethod, place a length of the Plastigage of proper gaugeacross the bearing. Then, assemble the bearing cap andtighten it in place. DO NOT TURN the crankshaft, asthat will destroy the Plastigage. After you install andproperly fasten the bearing cap, remove it. Compare thewidth of the crushed Plastigage with the Plastigage chartto determine the exact clearance.You must take measurements at specified intervals,usually at every overhaul, to establish the amount ofbearing wear. Also take a sufficient number ofcrankshaft journal diameter measurements at suitablepoints to determine possible out-of-roundness.With some types of engines, a crankshaft bridgegauge (fig. 3-35) is used to check the wear of the mainbearing shells. To use the gauge, place it on thecrankshaft and measure the clearance between thebridge gauge and the shaft with a feeler gauge. Anyvariation between the measured clearance and thecorrect clearance (usually stamped on the housing ofeach bearing) indicates that main bearing wear hasoccurred. The maximum limits of wear are listed in themanufacturer’s technical manual. Some enginemanufacturers recommend that bridge gauge readingsbe taken at every overhaul in conjunction with crankweb deflection measurements.The important point to remember is that if youcannot overhaul an engine due to lack of space,manpower, or expertise, you may request outside helpby using an OPNAV Form 4790/2K. This form, whenused as a work request, will be sent to a ship intermediatemaintenance activity (SIMA). The SIMA will thenaccept or reject the work request. If the work request isaccepted, the SIMA will order all repair parts, overhaulthe engine, and perform an operational test according tothe manufacturers’ technical manuals and the NSTM,chapter 233.As stated earlier in this section, maintenance cards,manufacturers’ maintenance manuals, and various otherinstructions discuss repair procedures in detail.Therefore, this chapter will be limited to generalinformation on some of the troubles encountered duringoverhaul, the causes of such troubles, and the methodsof repair.TROUBLESHOOTINGINTERNAL-COMBUSTION ENGINESTheproceduresfortroubleshootinginternal-combustion engines are somewhat similar forboth diesel and gasoline engines. In many instances, theinformation that follows will apply to both types ofengine. However, it also discusses principal differences.Since most of the internal-combustion engines used bythe Navy are diesel, the following sections dealprimarily with this type of engine.This chapter is concerned with troubles that occurboth when an engine is starting and running. Thetroubles are chiefly the kind that can be identified byerratic engine operation, warnings by instruments, orinspection of the engine parts and systems and that canbe corrected without major repair or overhaul. There isalso a section devoted to the systems of the gasolineengine that are basically different from those of thediesel engine.Keep in mind that the troubles listed here are generaland may or may not apply to a particular diesel engine.When you work with a specific engine, check themanufacturer’s technical manual and any instructionsissued by the Naval Sea Systems Command.An engine may continue to operate even when aserious casualty is imminent. However, symptoms areusually present. Your success as a troubleshooterdepends partially upon your ability to recognize thesesymptoms when they occur. You will use most of yoursenses to detect trouble symptoms. You may see, hear,smell, or feel the warning of trouble to come. Of course,common sense is also a requisite. Another factor in yoursuccess as a troubleshooter is your ability to locate thetrouble once you decide something is wrong with theequipment. Then, you must be able to determine asrapidly as possible what corrective action to take. In3-22
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