TM 1-1500-204-23-1 c. Sudden  Reduction  in  Engine  RPM.    When  the propeller or rotor strikes a small object which results in a sudden  reduction  In  engine  rpm,  the  engine  shall  be thoroughly checked using the following procedures: (1) Make a thorough external examination of engine    crankcase    and    nose    section    to    determine whether any parts have been damaged.  When damage is found which cannot be corrected by line maintenance, remove engine. (2) Remove magnetic sump plugs, If present, and engine oil screens or filters.  Examine for presence of metal particles. (3) Remove engine sump plugs, drain oil into a   clean   container,   strain   through   a   clean   cloth,   and examine cloth and strained oil for metal particles. NOTE ·  Metal particles found In the sumps or In  oil  screens  or  filters  will  not  be considered  the  results  of  an  Internal failure  caused  by  sudden  stoppage, since    the    screens    or    filters    are located at the oil inlet to the engine. Sudden  stoppage,  therefore,  will  not permit   circulation   of   the   oil   to   the extent  that  metal  particles  would  be deposited on the screens or filters. ·    When     heavy     metal     particles     are found In the oil, It indicates a definite engine  failure,  and  engine  must  be removed.         However,   when   metal particles  present  are  similar  to  fine filings, continue examination of engine to determine its serviceability. (4) Remove propeller and examine crankshaft,   or   propeller   drive   shaft   on   reduction-gear engines, for misalignment. (5) Clamp  a  test  indicator  to  nose  section  of engine and remove front or outside spark plugs from all cylinders  on  radial  engines  and  top  spark  plugs  on  all opposed engines. (6) Turn crankshaft and observe if crankshaft or propeller shaft runs out at either front or rear propeller cone seat location, as shown In figure 7-21. NOTE ·    When  there  is  runout  of  more  than 0.015    inch  full  indicator  reading  of crankshaft or propeller drive shaft at front    cone    seat    location,    remove engine.        Even    though    runout    of crankshaft or propeller drive shaft at front   cone   seat   is   less   than   0   015 inch  full  indicator  reading,  examine rear cone seat location. ·    When   any   runout   is   found   at   rear cone  seat  location,  which  Is  not  In same  plane  as  runout  at  front  cone seat location, remove engine. ·    When   crankshaft   or   propeller   drive shaft  runout  does  not  exceed  these limits,   install   serviceable   propeller and   make   an   additional   check   by tracking    propeller    at    tip    in    same plane perpendicular to axis of rotation   to   assure   that   blade   track tolerance Is within limits. (7) Start   engine   and   examine   for   smooth operation  and  adequate  power  output.    When  engine operates properly during this ground check, shut engine off and again examine oil system for metal particles. Figure 7-21.  Checking Propeller Shaft Runout 7-24