rapidly than a larger one, because the space available fordirt accumulation is more limited. There are twostandardized sizes of fuel filter elements-large andsmall. The small element is the same diameter as thelarge but is only one-half as long. This constructionpermits substitution of two small elements for one largeelement.You can increase the interval of time betweenelement changes by using the drain cocks on a filtersump. Removal of dirt through the drain cock will makeroom for more dirt to collect.If new filter elements are not available forreplacement and the engine must be operated, you canwash some types of totally clogged elements and getlimited additional service. This procedure is foremergencies only. An engine must never be operatedunless all the fuel is filtered; therefore, a “washed filter”is better than none at all.Fuel must never flow from the supply tanks to thenozzles without passing through all stages of filtration.Strainers, as the primary stage in the fuel filtrationsystem, must be kept in good condition if sufficient fuelis to flow in the system. Most strainers have a blademechanism that can be turned by hand. If you cannotreadily turn the scraper by hand, disassemble and cleanthe strainer. This minor preventive maintenance willprevent the scraping mechanism from breaking.TRANSFER PUMPS.—If the supply of fuel oil tothe system is to be maintained in an even anduninterrupted flow, the fuel transfer pumps mustfunction properly. These pumps may becomeinoperative or defective to the point that they fail todischarge sufficient fuel for engine starting. Generally,when a pump fails to operate, some parts have to bereplaced or reconditioned. For some types of pump, it iscustomary to replace the entire unit. However, for wornpacking or seals, satisfactory repairs may be made. Ifplunger-type pumps fail to operate because the valveshave become dirty, submerge and clean the pump in abath of diesel oil.Repairs of fuel transfer pumps should be madeaccording to maintenance manuals supplied by theindividual pump manufacturers.Malfunctioning of the Injection SystemThe fuel injection system is the most intricate of thesystems in a diesel engine. Since the function of aninjection system is to deliver fuel to the cylinder at a highpressure, at the proper time, in the proper quantity, andproperly atomized, special care and precautions must betaken in making adjustments and repairs.HIGH-PRESSURE PUMP.-If a high-pressurepump in a fuel injection system becomes inoperative, anengine may fail to start. Information on the causes andremedies for an inoperative pump can be found in themanufacturer’s technical manual. Any ship using fuelinjection equipment should have available copies of theapplicable manufacturer’s technical manual.TIMING.-Regardless of the installation or the typeof fuel injection system used, the timing of the injectionsystem must be correct to obtain maximum energy fromthe fuel. Early or late injection timing may prevent anengine from starting. Operation will be uneven andvibration will be greater than usual.If fuel enters a cylinder too early, detonationgenerally occurs, causing the gas pressure to rise toorapidly before the piston reaches top dead center. Thisin turn causes a loss of power and high combustionpressure. Low exhaust temperature may be an indicationthat fuel injection is too early.If fuel is injected too late in the engine cycle,overheating, lowered firing pressure, smoky exhaust,high exhaust temperature, or loss of power may occur.Follow the instructions in the manufacturer’stechnical manual to correct an improperly timedinjection system.Insufficient CompressionProper compression pressures are essential if adiesel engine is to operate satisfactorily. Insufficientcompression may cause an engine to fail to start. If yoususpect low pressure as the reason, check thecompression with the appropriate instrument. If the testindicates pressures below standard, disassembly isrequired for complete inspection and correction.Inoperative Engine GovernorThere are many troubles that may cause a governorto become inoperative. The most frequent troubleassociated with starting an engine is generally caused bybound control linkage or, if the governor is hydraulic,by low oil level. Whether the governor is mechanical orhydraulic, binding of linkage is generally due todistorted, misaligned, defective, or dirty parts. If yoususpect binding, move the linkage and governor partsby hand and check their movement. Eliminate anyundue stiffness or sluggishness in the movement of thelinkage.3-29
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