CAUTION Do   not   submerge   armature,   or field   coils   in   solvent. 2.   Clean   field   coils   and   frame   thoroughly with  a  cloth  dampened  with  cleaning  solvent  Federal Specification  P-D-680. Dry  thoroughly  with  comp- ressed   air. 3.   Remove   loose   particles   from   arma- ture  with  compressed  air  and  wipe  with  a  clean  cloth dampened   with   cleaning   solvent.   Clean   commutator lightly  with  number  00  sandpaper  and  remove  all traces  of  dust  with  low-pressure  compressed  air. 4.   Clean   brush   holders   with   a   brush   and cleaning  solvent,  Federal  Specification  P-D-680,  and dry   them   thoroughly   with   compressed   air. 5.   Clean   brushes   with   a   clean,   dry   cloth only.  Do  not  permit  cleaning  solvent  to  come  in  con- tact   with   the   brushes. (b)    Inspection. 1.   Test   field   coils   for   insulation   break- down  with  megger  connected  between  frame  and  one coil   terminal.   Minimum   resistance   reading   permis- sible  is  one  megohm. Replace   motor   assembly   if   coil is   defective. 2.   Test   armature   for   grounds   with   a   test light.   Touch   a   test   light   probe   to   the   armature   core and   the   other   probe   to   a   commutator   bar   riser.   If test   light   glows,   armature   is   grounded.   Repeat   test for   all   commutator   bars. 3.   Test   armature   for   short   circuits   using a   growler   fixture. (4)   Repair. (a)  Housing  and  commutator  end  head. 1.   Smooth   minor   scratches   burrs,   and dents  on  machined  surfaces  using  a  fine  mill  file. 2.   Repair   damaged   threads. (b)    Armature. 1.   Resurface   commutator   by   removing   no more  than  0.005  inch  during  any  one  cut  and  no  more than  0.002  inch  on  final  cut.  Check  that  the  final  dia- meter  of  commutator  is  not  less  than  0.  925  inches. 2.   If   commutator   diameter   is   satisfactory, undercut  mica  to  a  depth  of  0.  025  to  0.  032  inch  below commutator   surface. NOTE Use   care   in   undercutting.   Do   not   widen commutator   slots   by   removing   metal   from segments,  and  do  not  leave  thin  edge  of mica  next  to  segment. 3.   After   the   mica   has   been   undercut, remove   all   copper   and   mica   particles   with   compressed air. Polish  the  commutator  in  a  lathe  with  number 2/0   sandpaper   while   the   armature   is   rotating   at   1500 rpm.   After   polishing   the   armature,   check   that   com- mutator   diameter   is   not   less   than   0.   925   inches.   Re- place  if  diameter  is  less. 4.   After   repair   work   has   been   completed, repeat  steps  2  and  3  of  e(3)(a)  above. (c)   Field   coil   assembly. 1.   Smooth   minor   scratches,   burrs,   and nicks   on   machined   surfaces   of   frame   using   fine   mill file. 2.   Repair   damaged   threads   in   frame. 3.   Replace   motor   assembly   if   field   coil insulation   resistance   is   less   than   one   megohm. (5)    Reassembly. Reassemble  fan  and  mot  or assembly   in   reverse   order   of   disassembly. (6)   Bench   tests. (a)  Energize  the  fan  motor  with  115  Vdc. (b)  Check  the  speed  of  the  armature  on  the tachometer. Minimum  speed  should  be  3600  rpm. (c)   Check   the   current   draw   on   the   ammeter. Maximum   current   draw   should   be   1.8   amperes. (7)   Installation. Refer   to   Operator   and   Organ- izational  Maintenance  Manual  and  install  the  fan  and motor   assembly. f.   Circuit   Breaker.   Refer   to   Operator   and   Org- animational   Maintenance   Manual. g.   Indicator   Light.   Refer   to   Operator   and   Organ- izational    Maintenance    Manual. h.  Load  Reject  Switch.  Refer  to  Operator  and Organizational    Maintenance    Manual. i.   Terminal   Board.   Refer   to   Operator   and   Org- anizational    Maintenance    Manual. j.   Thermostat. Refer   to   Operator   and   Organi- zational   Maintenance   Manual. k.   Heater   Elements. Refer   to   Operator   and Organizational    Maintenance    Manual. l.   Replace   all   Defective   Components. 17-27.   Reassembly   and   Installation. a.   Reassembly. See  figure  17-7  and  the  Operator and   Organizational   Maintenance   Manual   and   reassem- ble  the  load  bank. b.    Installation. Refer  to  the  Operator  and  Org- anizational   Maintenance   Manual   and   install   the   load bank   on   the   generator   set. 17-17