TM 10-3930-671-24 BEARINGS Tri-metal   bearings   when   new   are   smooth   and   highly polished.    However,  a  very  few  hours  of  operation  will change their appearance completely.  The bearing surface  becomes  a  leaden  gray  in  color  and  develops minute   craters,   almost   cellular   in   appearance.      This appearance   is   a   natural   characteristic   of   this   type   of bearing and in no way indicates failure. 7. If the visual inspection appears satisfactory, they should  be  removed  and  checked  for  thickness using a ball micrometer. To  remove  the  upper  half  of  the  bearing  shell   use   a special tool obtainable at most  parts  houses,  which  is  a pin  with  an  angular  head.    It  may  be  inserted  in  the  oil hole of the crankshaft and as the crankshaft is turned in a  clockwise  direction,  the  head  of  this  pin  picks  up  the bearing  shell  and  forces  it  out  of  the  bore  in  the  block. The thickness of the bearing shells is given in the Limits and   Clearance   Chart,   and   if   this   thickness   has   been reduced    more    than    0.013mm    (.0005’)    beyond    the maximum allowable tolerance the bearing shell must be replaced. CAUTION The   upper   main   bearing   shells   are grooved.      The   lower   main   bearing shells  on  some  models,  are  not.  The ungrooved    bearing    shell    must    be placed  in  the  bearing  cap,  not  In  the block, or oil to the bearing will be cut off and damage to engine will result. 8. If  visual  inspection  of  the  crankshaft  shows  no indication   of   excessive   wear    or    scoring,    the clearance of the bearing should be checked. F-179