all   points.   In   service,   the   best   indication   of   good alignment   is   good   tooth   contact. The   technical   manual   furnished   with   each   gear installation  describes  the  procedures  for  determining  the proper  depth  of  mesh  and  parallelism  of  gear  and  pinion shafts.  The  length  of  tooth  contact  across  the  face  of  the gear   teeth   is   the   key   to   satisfactory   alignment   of reduction  gears. Poor  alignment  between  the  line  shaft  and  the  MRG may  be  detected  at  the  reduction  gear.  Uneven  loading of  the  low-speed  gear  train  and  noisy  operation  in  certain speed  ranges  are  two  common  results  of  poor  line  shaft to   MRG   alignment. The  most  favorable  alignment  position  of  the  main engine  to  the  reduction  gear  is  when  they  are  concentric at   full   power   at   the   proper   operating   temperature.   The flexible   high-speed   coupling   is   designed   to   handle   the transient   condition   of   slight   misalignments   as   the machinery  comes  up  to  temperature.  The  two  most common  forms  of  misalignment  between  the  prime mover  and  the  driven  shafts  are  angular  and  parallel offset,  as  shown  in  figure  3-5. The  object  of  the  alignment  is  to  locate  the  turbine so   the   axis   of   the   spindle   will   be   concentric   with   and parallel   to   the   axis   of   the   reduction   gear   input   pinion shaft.   Attaining   alignment   is   complicated   by   the   fact that   the   turbine,   reduction   gear,   and   foundations   all

expand   as   they   are   heated   during   operation   to   the   hot running  conition.  Another  factor  is  when  operating pinion   shafts   move   higher   in   their   bearings   under   the influence   of   the   hydrodynamic   oil   film   and   tooth pressure.   These   changes   in   position   have   been predetermined  by  the  manufacturer,  and  you  can  find the   offset   readings   in   the   appropriate   technical   manual for   the   installation. MAIN   THRUST   BEARING   CLEARANCE MEASUREMENTS As   you   have   already   learned   in   Gas   Turbine Systems   Technician   (Electrical)   3/Gas   Turbine   Systems Technician   (Mechanical)   3,   volume   1,   NAVEDTRA 10563,   propeller   thrust   is   transferred   from   each propulsion   shaft   to   the   hull   through   a   Kingsbury   main thrust   bearing   (fig.   3-6).   The   Kingsbury   thrust   bearing uses   the   wedge-shaped   oil   film   lubrication   principle. This   principle   is   based   on   an   oil   film   between   two sliding  surfaces  tends  to  assume  a  tapered  depth  with  the thicker   film   at   the   entering   side.   In   a   Kingsbury assembly,  eight  bearing  shoes  are  installed  on  each  side of   the   thrust   collar.   Therefore,   eight   separate wedge-shaped  oil  films  are  installed  on  each  thrust  face. Since  the  bearing  shoes  are  free  to  tilt  slightly,  the  oil automatically  assumes  the  taper  required  by  shaft  speed, loading,   and   oil   viscosity. The  main  thrust  bearing  assembly  consists  of  the bearing   housing,   two   thrust   rings,   and   a   thrust   collar. The   housing,   thrust   rings,   and   thrust   collar   facings   are all  split  horizontally.  Each  thrust  ring  is  made  up  of  8 steel   thrust   shoes   with   tin   babbitt   facings,   16   leveling plates,  and  a  retainer  ring.  The  thrust  collar  has  a two-piece   removable   steel   thrust   face   attached   to   each side.  Each  thrust  shoe  contains  a  hardened  shoe  support with   a   spherical   face.   The   support   bears   on   the   upper leveling  plate  and  the  spherical  face  allow  the  thrust shoe   to   pivot   or   tilt   slightly   in   all   directions.   This arrangement   allows   the   bearing   to   operate   on   the free-wedge  film  lubrication  principle.  One  thrust  shoe on   each   side   is   fitted   with   a   resistance   temperature element  (RTE). Due   to   the   spring   isolation   system,   main   thrust bearing   clearance   measurements   are   no   longer   taken with   a   depth   micrometer.   All   measurements   are   now taken  with  a  dial  indicator  that  measures  the  deflection of  the  propulsion  shaft  at  the  main  flange.  There  are  two methods   (static   and   dynamic)   used   to   create   shaft deflection.  The  method  used  depends  on  the  ship  class. The   static   method   must   be   used   on   CG-66   and   above and  all  DDG-51  class  ships.  

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