rapidly than a larger one, because the space available for dirt  accumulation  is  more  limited.  There  are  two standardized  sizes  of  fuel  filter  elements-large  and small.  The  small  element  is  the  same  diameter  as  the large  but  is  only  one-half  as  long.  This  construction permits  substitution  of  two  small  elements  for  one  large element. You  can  increase  the  interval  of  time  between element  changes  by  using  the  drain  cocks  on  a  filter sump. Removal of dirt through the drain cock will make room for more dirt to collect. If  new  filter  elements  are  not  available  for replacement and the engine must be operated, you can wash  some  types  of  totally  clogged  elements  and  get limited   additional   service.   This   procedure   is   for emergencies  only.  An  engine  must  never  be  operated unless all the fuel is filtered; therefore, a “washed filter” is better than none at all. Fuel must never flow from the supply tanks to the nozzles without passing through all stages of filtration. Strainers,  as  the  primary  stage  in  the  fuel  filtration system, must be kept in good condition if sufficient fuel is  to  flow  in  the  system.  Most  strainers  have  a  blade mechanism that can be turned by hand. If you cannot readily turn the scraper by hand, disassemble and clean the  strainer.  This  minor  preventive  maintenance  will prevent the scraping mechanism from breaking. TRANSFER  PUMPS.—If  the  supply  of  fuel  oil  to the  system  is  to  be  maintained  in  an  even  and uninterrupted  flow,  the  fuel  transfer  pumps  must function   properly.   These   pumps   may   become inoperative  or  defective  to  the  point  that  they  fail  to discharge sufficient fuel for engine starting. Generally, when  a  pump  fails  to  operate,  some  parts  have  to  be replaced or reconditioned. For some types of pump, it is customary to replace the entire unit. However, for worn packing  or  seals,  satisfactory  repairs  may  be  made.  If plunger-type pumps fail to operate because the valves have become dirty, submerge and clean the pump in a bath of diesel oil. Repairs  of  fuel  transfer  pumps  should  be  made according  to  maintenance  manuals  supplied  by  the individual pump manufacturers. Malfunctioning of the Injection System The fuel injection system is the most intricate of the systems  in  a  diesel  engine.  Since  the  function  of  an injection system is to deliver fuel to the cylinder at a high pressure, at the proper time, in the proper quantity, and properly atomized, special care and precautions must be taken in making adjustments and repairs. HIGH-PRESSURE  PUMP.-If  a  high-pressure pump in a fuel injection system becomes inoperative, an engine may fail to start. Information on the causes and remedies for an inoperative pump can be found in the manufacturer’s technical manual. Any ship using fuel injection  equipment  should  have  available  copies  of  the applicable manufacturer’s technical manual. TIMING.-Regardless of the installation or the type of fuel injection system used, the timing of the injection system must be correct to obtain maximum energy from the fuel. Early or late injection timing may prevent an engine  from  starting.  Operation  will  be  uneven  and vibration will be greater than usual. If   fuel   enters   a   cylinder   too   early,   detonation generally  occurs,  causing  the  gas  pressure  to  rise  too rapidly before the piston reaches top dead center. This in  turn  causes  a  loss  of  power  and  high  combustion pressure. Low exhaust temperature may be an indication that 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’s technical   manual   to   correct   an   improperly   timed injection   system. Insufficient Compression Proper  compression  pressures  are  essential  if  a diesel  engine  is  to  operate  satisfactorily.  Insufficient compression may cause an engine to fail to start. If you suspect   low   pressure   as   the   reason,   check   the compression  with  the  appropriate  instrument.  If  the  test indicates   pressures   below   standard,   disassembly   is required for complete inspection and correction. Inoperative Engine Governor There are many troubles that may cause a governor to   become   inoperative.   The   most   frequent   trouble associated with starting an engine is generally caused by bound control linkage or, if the governor is hydraulic, by low oil level. Whether the governor is mechanical or hydraulic,  binding  of  linkage  is  generally  due  to distorted,  misaligned,  defective,  or  dirty  parts.  If  you suspect binding, move the linkage and governor parts by  hand  and  check  their  movement.  Eliminate  any undue stiffness or sluggishness in the movement of the linkage. 3-29