The gases burn the valve and seat and may cause a leakbetween these two surfaces even though the originalcauses of the sticking are eliminated.Completely disassemble and inspect a leakingvalve. It is subject to a resinous deposit similar to thatfound in a pressure-actuated air valve. Use a specifiedcleaning compound to remove the deposit. Be sure thevalve stem is not bent. Check the valve and valve seatsurfaces carefully. Eliminate scoring or discoloration bylapping with a fine lapping compound. You may usejewelers’ rouge or talcum powder with fuel oil forlapping.From the preceding discussion, you have learnedthat the air starting system may be the source of manytroubles that will prevent an engine from cranking eventhough it can be barred over. You will avoid a few ofthese troubles by following prestarting and startinginstructions. One such instruction, sometimesoverlooked, is that of opening the valve in the air line.Obviously, with this valve closed the engine will notcrank. Recheck the instructions for such oversights as aclosed valve, an empty air storage receiver, or anengaged jacking gear before starting any disassembly.ELECTRIC START MALFUNCTIONElectric starting system malfunctions fall into thefollowing categories:1. Nothing happens when the starter switch isclosed.2. The starter motor runs, but it does not engage theengine.3. The starter motor engages, but it cannot turn theengine.If nothing happens when you close the starterswitch, there is a failure in the electrical system. Thefailure could be an open circuit caused by brokenconnections or burned out components. Test the circuitcontinuity to make sure the relay closes and the batteryprovides sufficient voltage and current to the startercircuit. If the circuit is complete, there may be resistancethrough faulty battery connections. Considerablecurrent is needed to operate the solenoid and startermotor.If the starter runs without engaging, it will producea distinctive hum or whine. The lack of engagement isusually caused by dirt or corrosion, which keeps thesolenoid or Bendix gears from operating properly.If the starter motor engages the flywheel ring gearbut is not able to turn the engine or cannot turn it quicklyenough to obtain starting speed, the cause may be lackof battery power or, more likely, a mechanical problem.If the engine can be barred over, there is excessivefriction in the meshing of the starter pinion and the ringgear. Either the teeth are burred, or the starter pinion isout of alignment. Either case would have been precededby noise the last time the starter was used. A major repairmay be necessary.Other problems and malfunctions of electricstarting systems are discussed in association withgasoline engines at the end of this chapter.ENGINE CRANKS BUT FAILS TO STARTEven when the starting equipment is in an operatingcondition, an engine may fail to start. Most troubles thatprevent an engine from starting are associated with fueland the fuel system. However, defective or inoperativeparts or assemblies may be the source of some trouble.Failure to follow instructions may be the cause of anengine failing to start. The corrective action is obviousfor such items as leaving the fuel throttle in the OFFposition and leaving the cylinder indicator valves open.If an engine fails to start, follow the prescribed startinginstructions and recheck the procedure.Foreign Matter in the Fuel Oil SystemIn the operation of an internal-combustion engine,cleanliness is of paramount importance. This isespecially true in the handling and care of diesel fuel oil.Impurities are the prime source of fuel pump andinjection system troubles. Sediment and water causewear, gumming, corrosion, and rust in a fuel system.Even though fuel oil is generally delivered clean fromthe refinery, handling and transferring increase thechances that fuel oil will become contaminated.Corrosion often leads to replacement or at least torepair of the part. You must continually take steps toprevent water from accumulating in a fuel system, notonly to eliminate the cause of corrosion but also toensure proper combustion in the cylinders. Centrifugeall fuel, and drain the fuel filter cases periodically toprevent excessive collection of water.Water in fuel will cause irreparable damage to theentire fuel system in a short time. It corrodes the fuelinjection pump, where close clearances must bemaintained, and also corrodes and erodes the injectionnozzles. The slightest corrosion can cause a fuelinjection pump to bind and seize which, if not corrected,3-27
Integrated Publishing, Inc. - A (SDVOSB) Service Disabled Veteran Owned Small Business