TM 5-3820-241-34 ME  3820-241-34/5-10 Figure   5-10.   Removing   buffer   ring   assembly. 5-11.   Drifter   Drill   Cleaning,   Inspection   and Repair a.   General.   The   drill   engine   should   be disassembled   for   cleaning   and   inspection   at regular  intervals,  short  of  time  when  breakdown may  occur. Because   of   varied   operation   con- ditions,   inspection   periods   cannot   be   determined. They  can  only  be  arrived  at  with  accumulated experience  of  the  user,   until   safe   cleaning   and inspection  intervals  can  be  established.  Drills  in daily  service  must  be  returned  to  direct  and general   support   maintenance   for   disassembly, inspection   and   repair   as   required.   In   addition   a routine   inspection   for   signs   of   excessive   wear, scoring,   broken   or   cracked   parts   must   be   made. b.  Cleaning. (1)   Clean   all parts   except   O-rings   with cleaning   solvent   (Fed   Spec   PD   680)   and   dry thoroughly. (2)   Discard  and  replace  all  O-rings  and  seals. c.   Inspection   and   Repair. (1)  Buffer  R ing   Cylinder   and   Piston. (a)  The  most  frequent  reason  for  poor  drill performance   is   that   the   piston,   cylinder   or   buffer ring   lining   have   worn   to   such   an   extent   that   the clearance  between  then  has  increased  beyond  the allowable    wear limits. Excessive    clearance destroys   the   air   cushion   between   the   buffer   ring and   piston,   and   allows   the   piston   to   strike   the buffer   ring   with   considerable   impact,   and   often breaking   the   the   piston. (b)  Check  the  piston,  cylinder,  or  buffer ring  for  excessive  wear  by  applying  the  cushion test.   This   is   accomplished   by   dropping   the   free piston   in   the   cylinder.   The   piston   should   bounce or  cushion  on  the  air  trapped  between  the  piston head  and  buffer  ring.  If  the  piston  strikes  the buffer   ring   hard,   the   piston,   cylinder   lining   or buffer  ring  is  defective  and  worn  beyond  safe limits   and   they   must   be   replaced. (2)   Piston   Striking   Face. (a)   Inspect   the   piston   striking   face   to make  sure  it  is  not  chipped  or  cupped  excessively. A   defective   piston   will   damage   every   striking   bar with   which   it   comes   in   contact. A    stripped    or damaged   striking   bar   will   quickly   spoil   a   good piston. (b)   If   the   piston   striking   face   damage   has not   progressed   so   far,   it   can   be   repaired.   If   the piston  has  never  been  reground,  the  striking  face must   be   squared   up   and   flattened   by   careful grinding.   Perform   the   grinding   operation   slowly to   avoid   overheating   and   annealing   of   the   hard- ened  cast.  Do  not  grind  off  more  than  1/16-in.  of metal. (3)   Rifle   Nut   and   Chuck. (a)  Inspect  the  raffle  bar  for  a  good  fit  in the   rifle   nut,   allowable   wear   depends   to   some extent  on  drilling  conditions.  Lock  the  rifle  nut when  you  can  slide  a  1/8-in.  shim  between  the flutes   when   these   parts   are   engaged. (b)  Inspect  the  splines  in  the  chuck  nut  for excessive  wear.  The  piston  bears  on  the  splines  in the  chuck  nut  in  the  direction  of  rotation  only,  so more nut wear can be tolerated. Replace the chuck nut   if   wear   exceeds   1/2   the   thickness   of   the splines. (4)   Chuck   Parts. (a)   Inspect   the   chuck   and   chuck   bushing for  excessive  wear.  When  the  chuck  or  bushing  is worn,   alignment   of   the   drill   with   the   striking   bar cannot   be   maintained.   It   will   also   cause   chipping of  the  piston  or  striking  bar  and  may  shear  off  or punch   the   air   tube. (b)   Replace   a chuck   bushing   if   worn oversize  or  bell-mounted. (5)   Motor   Vanes. (a)   Inspect   the   motor   vanes   for   excessive wear.  If  the  laminations  show  any  sign  of separating,   discard   and   replace   with   an   complete new  set. (b)  Inspect  the  sides  of  the  vanes  for indication   of   excessive   milling.   When   a   maximum of  1/8-in.  of  the  original  vane  width  is  worn  away, 5-15