Chapter 3—ENGINE MAINTENANCEcommon rail system and the modified commonrail system.The fuel injection systems used on Atlasengines and some older models of Cooper-Bessemer engines are of the basic type. In thissystem one untimed, high-pressure pump suppliesfuel at injection pressure to a main header (com-mon rail). The fuel flows from the header to theinjector valves and nozzles at each cylinder. Theinjector valves are cam-operated and timed.Metering of the fuel is controlled by the lengthof time the nozzle remains open and by thepressure maintained by the high-pressure pumpin the common rail.The modified common rail system (constantpressure), found on newer models of Cooper-Bessemer engines, uses a high-pressure pump tomaintain fuel at the injection pressure in anaccumulator bottle. The fuel is metered byindividual valves mounted on the side of theengine; it then flows to the pressure-operatednozzles in the cylinder head, to be atomized anddistributed in the cylinder.Since complete details for the maintenance andrepair of each of the various fuel systems in serv-ice are beyond the scope of this book, specificinformation on a particular fuel injection systemmust come from the appropriate manufacturer’stechnical manual.FUEL INJECTION PUMPSAND INJECTORSIn any discussion of a fuel system, the impor-tance of each of its parts cannot be overlooked.The first requirement for trouble-free operationof a fuel system is clean fuel. Accordingly, thefilters, the strainers, the tanks, the transfer pumps,and the lines must be maintained according toprescribed instructions. Even when these partsfunction properly, the principal elements of theinjection system—pressure pump, injectionvalves, and injection nozzles—are subject totroubles. The following discussion covers someof these troubles, their symptoms and causes, andprovides general information concerningmaintenance and repair of this equipment. As youstudy this information, keep in mind the dif-ferences which may exist between the varioussystems. (A system, for example, may be of thejerk pump or common rail type, or the pressurepump and the injector may be separate orcombined.)Damaged PlungerIn the plunger and barrel assembly of a high-pressure pump and in the plunger and bushingassembly of a unit injector, the symptoms andcauses of damage are similar.Damage may become apparent through erraticengine operation. Symptoms vary widely and mayinclude failure of the engine to develop full power,low exhaust temperature, low firing pressure forthe affected cylinder, difficulty in balancing(calibrating) the pumps or injectors, and failureof one or more cylinders of the engine to fire.Damage to a plunger and the part in which it slidesmay also be recognized by testing the unit on atest stand. However, the best way to determinethe extent of damage is to disassemble the unit,clean it thoroughly, and then carefully inspecteach part.Cleaning of the units can be best accomplishedby use of an approved solvent. Clean diesel fuelmay be used when more effective cleaners are notavailable. A brush must be used with diesel fueland even then, removal of gummy deposits is dif-ficult. Keep each plunger and barrel (bushing)together during the inspection to avoid improperassembly, as they are manufactured in matchedsets.The use of a magnifying glass during theexamination of a plunger will facilitate the detec-tion of damage. Inspect for fine scratches, dullsurface appearance, cracks, pit marks (usuallyaccompanied by dark discoloration), and erosionand roughness at the edge of the helix or at theend of the plunger. An example of a badly scoredplunger is illustrated in A of figure 3-14.A plunger with the lapped surface and helix edgein good condition is shown in B of figure 3-14.Surface irregularities in the region illustrated areserious because they affect metering and, conse-quently, engine operation.When examining a barrel or bushing, searchfor erosion of the ports or scoring of the lappedsurfaces. Pay particular attention to the lappedplane surface at the end of a pump barrel. Rustor pit marks on this surface must be removed bylapping before reassembly.3-17
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