ENGINEMAN  1  &  C Trouble Dirty   bearing Spalled   or   pitted rollers   or   races Dented    (brinelled) r a c e s Failed   separator Races  abraded  on external   surfaces Cracked   race Excessive looseness Causes Improper  handling  or storage Use   of   dirty   or   improper lubricant Failure  to  clean  housing Poor   condition   of   seal Dirt  in  bearing Water  in  bearing Improper   adjustment   of tapered   roller   bearings Bearing   misaligned   or   off square Improper   installation   or removal Vibration  while  bearing  is inoperative Initial  damage  during  in- stallation   or   removal Dirt  in  the  bearing Locked  bearing Improper  fit  of  races Improper   installation   or removal    (cocking) Abrasives   in   lubricant Figure 3-23.—Antifriction bearing troubles and their causes. Brinelled   or   dented   races   are   most   easily recognized  by  inspection  after  a  thorough  clean- ing. Brinelling receives its name from its similarity to the Brinnell hardness test, in which a hardened ball  is  pressed  into  the  material.  The  diameter  of the  indentation  is  used  to  indicate  the  hardness of  the  material.  Bearing  races  may  be  brinelled by  excessive  and  undue  pressures  during  installa- tion  or  removal,  or  by  vibration  from  other machinery  while  the  bearing  is  inoperative.  If heavy shafts supported by frictionless bearings are allowed  to  stand  motionless  for  a  long  time,  and if  the  equipment  is  subject  to  considerable  vibra- tion, brinelling may occur. This is due to the peen- ing  action  of  the  rollers  or  balls  on  the  races. 3-36 Brinelled bearings must not be placed back in service.  Steps  can  be  taken  to  prevent  brinelling. Proper  maintenance  will  help  a  great  deal,  and the   best   insurance   against   brinelling   caused   by vibration  is  to  rotate  the  shafts  supported  by  the frictionless  bearings  at  regular  intervals  (at  least once  a  day)  during  periods  of  idleness.  These actions  will  prevent  the  rollers  from  resting  too long  upon  the  same  portion  of  the  races. Separator  failure  may  become  apparent  by noisy  operation.  Inspection  of  the  bearings  may reveal loose rivets, failure of a spot weld, or crack- ing  and  distortion  of  the  separator.  Failure  of separators   can   usually   be   avoided   if   proper installation  and  removal  procedure  are  followed, and  steps  are  taken  to  exclude  the  entry  of  dirt. Abrasion  (scoring,  wiping,  burnishing)  on  the external  surface  of  a  race  indicates  that  relative motion   has   occurred   between   the   race   and   the bearing  housing  or  shaft  surface.  The  race  adja- cent  to  the  stationary  member  is  usually  made  a push  fit  so  that  some  creep  will  occur.  Creep  is a very gradual rotation of the race. This extremely slow  rotation  is  desirable  as  it  prevents  repeated stressing   of   the   same   portion   of   the   stationary race.  Wear  resulting  from  the  proper  creep  is negligible   and   no   damaging   abrasion   occurs. However,  abrasion  caused  by  locked  bearings  or the  improper  fit  of  the  races  must  be  prevented. Cracked  races  will  usually  be  recognized  by a  definite  thump  or  clicking  noise  in  the  bearing during  operation.  Cleaning  and  inspection  is  the best  means  of  determining  if  cracks  exist.  Cracks usually  form  parallel  to  the  axis  of  the  race.  The cracking  of  bearing  races  seldom  occurs  if proper   installation   and   removal   procedures   are followed. Excessive  looseness  may  occur  on  rare  occa- sions   even   though   no   surface   disintegration   is apparent.  Since  many  frictionless  bearings  appear to  be  loose,  even  when  new,  looseness  is  not always a sign of wear. The best check for excessive looseness is to compare the suspected bearing with a  new  one. Wear   of   bearings,   which   cause   looseness without   apparent   surface   disintegration,   is generally caused by the presence of fine abrasives in the lubricant. Taking steps to exclude abrasives and  keeping  lubricating  oil  filters  and  strainers  in good condition is the best way to prevent this type of  trouble.