Figure 3-35.—Crankshaft bridge gauge. leave an impression in the soft bearing metal because the gauge material is softer than the bearing. To use this method, place a length of the Plastigage of proper gauge across the bearing. Then, assemble the bearing cap and tighten it in place. DO NOT TURN the crankshaft, as that  will  destroy  the  Plastigage.  After  you  install  and properly fasten the bearing cap, remove it. Compare the width of the crushed Plastigage with the Plastigage chart to determine the exact clearance. You  must  take  measurements  at  specified  intervals, usually  at  every  overhaul,  to  establish  the  amount  of bearing  wear.  Also  take  a  sufficient  number  of crankshaft  journal  diameter  measurements  at  suitable points  to  determine  possible  out-of-roundness. With  some  types  of  engines,  a  crankshaft  bridge gauge (fig. 3-35) is used to check the wear of the main bearing   shells.   To   use   the   gauge,   place   it   on   the crankshaft   and   measure   the   clearance   between   the bridge  gauge  and  the  shaft  with  a  feeler  gauge.  Any variation   between   the   measured   clearance   and   the correct  clearance  (usually  stamped  on  the  housing  of each  bearing)  indicates  that  main  bearing  wear  has occurred. The maximum limits of wear are listed in the manufacturer’s   technical   manual.   Some   engine manufacturers recommend that bridge gauge readings be  taken  at  every  overhaul  in  conjunction  with  crank web  deflection  measurements. The  important  point  to  remember  is  that  if  you cannot  overhaul  an  engine  due  to  lack  of  space, manpower, or expertise, you may request outside help by using an OPNAV Form 4790/2K. This form, when used as a work request, will be sent to a ship intermediate maintenance  activity  (SIMA).  The  SIMA  will  then accept or reject the work request. If the work request is accepted,  the  SIMA  will  order  all  repair  parts,  overhaul the engine, and perform an operational test according to the manufacturers’ technical manuals and the NSTM, chapter  233. As  stated  earlier  in  this  section,  maintenance  cards, manufacturers’  maintenance  manuals,  and  various  other instructions  discuss  repair  procedures  in  detail. Therefore,   this   chapter   will   be   limited   to   general information on some of the troubles encountered during overhaul, the causes of such troubles, and the methods of repair. TROUBLESHOOTING INTERNAL-COMBUSTION  ENGINES The procedures for troubleshooting internal-combustion engines are somewhat similar for both diesel and gasoline engines. In many instances, the information  that  follows  will  apply  to  both  types  of engine. However, it also discusses principal differences. Since most of the internal-combustion engines used by the  Navy  are  diesel,  the  following  sections  deal primarily with this type of engine. This chapter is concerned with troubles that occur both  when  an  engine  is  starting  and  running.  The troubles are chiefly the kind that can be identified by erratic  engine  operation,  warnings  by  instruments,  or inspection of the engine parts and systems and that can be corrected without major repair or overhaul. There is also a section devoted to the systems of the gasoline engine  that  are  basically  different  from  those  of  the diesel  engine. Keep in mind that the troubles listed here are general and may or may not apply to a particular diesel engine. When  you  work  with  a  specific  engine,  check  the manufacturer’s technical manual and any instructions issued by the Naval Sea Systems Command. An  engine  may  continue  to  operate  even  when  a serious casualty is imminent. However, symptoms are usually   present.   Your   success   as   a   troubleshooter depends partially upon your ability to recognize these symptoms when they occur. You will use most of your senses to detect trouble symptoms. You may see, hear, smell, or feel the warning of trouble to come. Of course, common sense is also a requisite. Another factor in your success as a troubleshooter is your ability to locate the trouble once you decide something is wrong with the equipment.  Then,  you  must  be  able  to  determine  as rapidly  as  possible  what  corrective  action  to  take.  In 3-22