learning  to  recognize  and  locate  engine  troubles, experience is the best teacher. Instruments  play  an  important  part  in  detecting engine troubles. You should read the instruments and record  their  indications  regularly.  If  the  recorded indications   vary   radically   from   those   specified   by engine  operating  instructions,  the  engine  is  not operating properly and some type of corrective action must   be   taken.   You   must   be   familiar   with   the specifications   in   the   engine   operating   instructions, especially those pertaining to temperatures, pressures, and speeds. You should know the probable effect on the engine when instrument indications vary considerably from  the  specified  values.  When  variations  occur  in instrument  indications,  before  taking  any  corrective action be sure the instruments are not at fault before you try  corrective  actions  on  the  engine.  Check  the instruments immediately if you suspect them of being inaccurate. Periodic  inspections  are  also  important  in  detecting engine  troubles.  Such  inspections  will  reveal  the  failure of visible parts, presence of smoke, or leakage of oil, fuel, or water. Cleanliness is probably one of the greatest aids  in  detecting  leakage. When you secure an engine because of trouble, your procedure  for  repairing  the  casualty  should  follow  an established pattern, if you have diagnosed the trouble. If you do not know the location of the trouble, find it. To  inspect  every  part  of  an  engine  whenever  trouble occurs would be an almost endless task. You can find the cause of the trouble much more quickly by following a  systematic  and  logical  method  of  inspection, Genernlly speaking, a well-trained troubleshooter can isolate  the  trouble  by  identifying  it  with  one  of  the engine systems. Once you have associated the trouble with a particular system, the next step is to trace out the system until you find the cause of the trouble. Troubles generally originate in only one system, but remember that troubles in one system may cause damage to another system   or   to   basic   engine   parts.   When   a   casualty involves more than one system of the engine, trace each system  separately  and  make  corrections  as  necessary.  It is  obvious  that  you  must  know  the  construction, function, and operation of the various systems as well as the parts of each system for a specific engine before you can satisfactorily locate and remedy troubles. Even though there are many troubles that may affect the   operation   of   a   diesel   engine,   satisfactory performance  depends  primarily  on  sufficiently  high compression pressure and injection of the right amount of fuel at the proper time. Proper compression depends basically on the pistons, piston rings, and valve gear, while the right amount of fuel obviously depends on the fuel  injectors  and  their  actuating  mechanism.  Such troubles  as  lack  of  engine  power,  unusual  or  erratic operation,  and  excessive  vibration  may  be  caused  by either  insufficient  compression  or  faulty  injector  action. You  can  avoid  many  troubles  by  following  the prescribed  instructions  for  starting  and  operating  the engine, The troubles discussed in the following sections do  not  comprise  a  complete  list,  nor  do  they  all necessarily   apply   to   all   diesel   engines   because   of differences   in   design.   Specific   information   on troubleshooting for all the diesel engines used by the Navy would require more space than is available here. Even though a successful troubleshooter generally associates certain troubles with a particular system or assembly,  the  following  sections  discuss  troubles according  to  when  they  might  be  encountered,  either before or after the engine starts. ENGINE  FAILS  TO  START In general, the troubles that prevent an engine from starting are (1) the engine can neither be cranked nor barred over, (2) the engine cannot be cranked, but it can be barred over, and (3) the engine can be cranked, but it still  fails  to  start.  Figure  3-36  illustrates  various conditions that commonly cause difficulties in cranking, jacking over, or starting the engine. Engine Cannot Be Cranked nor Barred Over Most   prestarting   instructions   for   large   engines require   you   to   turn   the   crankshaft   one   or   more revolutions   before   applying   starting   power.   If   you cannot turn the crankshaft over, check the turning gear to be sure it is properly engaged. If the turning gear is properly engaged and the crankshaft still fails to turn over, check to see whether the cylinder test valves or indicator valves are closed and are holding water or oil in the cylinder. When the turning gear operates properly and the cylinder test valves are open but the engine still cannot be cranked or barred over, check for a serious problem.  A  piston  or  other  part  may  be  seized  or  a bearing may be fitting too tightly. Sometimes you may need  to  remove  a  part  of  an  assembly  to  remedy  the difficulty. 3-23