at  the  top  of  insert  seat.  Thus,  for  the  30°  exhaust valve  face  angle  and  a  1°  interference  angle,  the  in- sert  seat  grinder  wheel  must  be  dressed  to  grind  the insert  seat  at  an  axle  of  31°.  Likewise,  the  insert seat  for  the  intake  valve  must  be  ground  at  31  .  This is  a  positive  interference  angle.  A  negative  angle must  be  avoided.  The  first  step  in  reconditioning  a seat  or  insert  is  to  grind  the  seat,  removing  only enough  metal  to  produce  a  pit-free  continuous  seat. After  the  seat  has  been  ground,  use  a  dial  gauge  to check  concentricity  of  the  seat  relative  to  the  valve guide.  The  total  run-out  of  a  good  seat  should  not exceed 0. 002 inch total indicator reading. (3)  To  determine  seat  contact  in  relation  to insert  and  valve  face,  wipe  a  thin  film  of  Prussion Blue on the valve face and bounce the valve once on the valve  seat. A thin, continuous line must be evident on the  valve  face,  otherwise  further  grinding  is  required. NOTE Do not revolve valve while checking seat. (4) The width of the valve seat on both the ex- haust  and  service  intake  inserts  is  3/32  inch.  If  the seats  are  too  wide  or  too  narrow  they  must  be  ground to  the  proper  width  using  the  appropriate  angle  grind- ing wheels. CAUTION After  valves  are  installed  in  cylinder  head, make  certain  the  exhaust  valve  heads  are  set in a minimum of 0.053 inch and the intake valve  heads  are  set  in  a  minimum  of  0.054 inch  from  the  cylinder  head  gasket  surface, otherwise,   serious   damage   will   result.   If valve  stand  -in  is  less  than  the  allowable amount,  the  valve  seat  must  be  ground lower  until  the  allowable  stand-in  is  ob- tained. e.  Rocker  Arm,  Shaft  Inspection  and  Repair. (1)  Inspect  end  of  rocker  arm  adjusting  screws and  end  of  rocker  arms.  If  they  are  worn,  the  rocker arm  assemblies  must  be  replaced. (2)  Inspect  rocker  arm  shaft  bore  for  wear.  The bore  of  the  rocker  arm  bore  is  0.001  to  0.002  inches and  the  outer  diameter  of  the  rocker  arm  shaft  is 0.999  to  1.000  inch.  The  clearance  of  the  rocker  arm shaft  to  the  rocker  arm  is  0.001  to  0.003  inch  and  must not  exceed  0.  005  inch.  If  rocker  arm  shaft  bore  is  ex- cessively  worn,  the  rocker  arm  assemblies  must  be replaced. NOTE Bushings  are  non-replaceable  in  rocker arm   assemblies. (3)  Inspect  rocker  arm  shaft  for  wear  and  replace if   necessary.    Clean  oil  holes  in  rocker  arms  and  rocker shaft  with  solvent,  Federal  Specification  P-D-680,  a small   wire,   and   compressed   air. (4)  Inspect  both  ends  of  push  rods  for  signs  of wear.   Polish   out   nicks   or   scores. If  pushrods  are bent,  twisted,  or  damaged,  replace  push  rods. f.  Camshaft,  Camshaft  Gear  and  Valve  Lifter Inspection. (1)  The  outer  diameter  of  all  camshaft  bearing journals  is  2.130  to  2.131  inches.  The  inside  diameter of  the  camshaft  bearings,   when  installed,  is  2.133  to 2.136  inches. The  clearance  between  the  camshaft journals  and  bearings  is  0.002  to  0.006  inch  and  must not  exceed  0.008  inch.  If  exceeded  then  the  bearings must  be  replaced. If  the  installation  of  new  standard bearings  does  not  reduce  the  end  clearance  to  less than  0.  008  inch,  it  is  recommended  to  grind  the  cam- shaft  journals  to  accommodate  0.010-inch  undersize bearings. Likewise,  if  the  journals  are  worn  or scored  to  the  extent  that  they  will  not  accommodate 0.  010-inch  undersize  bearings,  the  camshaft  must  be replaced. (2)  Inspect  the  intake  and  exhaust  lobes  of  the camshaft  for  roughness,   scoring   or   excessive   wear. Replace  the  camshaft  if  any  of  these  conditions  are found to exist. (3)  Inspect  camshaft  gear  for  nicked,  scored, or   broken   teeth.   Replace   as   necessary. (4)  Inspect  thrust  plate  for  wear.  Replace  if  the wear  area  is  rough  or  the  wear  is  excessive.  New thrust  plate  thickness  is  0.204  to  0.206  inch. (5)  Inspect  valve  lifters  for  excessive  wear. Replace  a  set  of  lifters  if  one  or  more  show  excessive wear. 14-79.   Reassembly   and   Installation. a.   Valve   Lifter   Installation. — (1)  Lubricate  valve  lifters  with  clean  engine  oil and  install  them  in  their  original  positions  in  the  cyl- inder  block. (2)  Using  the  wooden  dowel  method  illustrated in  figure  14-40,  pull  the  lifters  up  so  they  do  not interfere   with   camshaft   installation. b.  Camshaft  and  Camshaft  Gear  Installation. — (1)  Place  the  camshaft  in  a  press  with  the shoulder  of  the  first  journal  resting  on  parallel  bars. (2)  Posit  Ion  the  thrust  plate  on  camshaft. Change   3   14-85