14-78.  Cleaning,  Inspection  and  Repair. a. from Cleani ng  and  Inspection  of  Cylinder  Head. (1)  Steam-clean  cylinder  head. (2)   Clean   deposits   of   salt,   lime   or   sludge water   jacket. (3)  Submerge  cylinder  head  in  tank  of  cleaning solution,   Federal   Specification   P-D-680   heated   to near  boiling  point. Remove  and  dry  thoroughly. (4)  Clean  crossheads,  valves,  and  valve springs   by   submerging   in   solvent.   Remove   from solvent  tank  and  dry  thoroughly. (5)  Clean  valves  with  buffer  and  polish  with crocus   cloth. (6)   Examine   cylinder   head   carefully   for   cracks. b.   Valve   Spring,   Valve  Guide,  Valve  Seat  and Valve   Inspection   and   Repair. (1)   Inspect   valve   springs   for   cracks.   Place spring   in   test   stand. Both  intake  and  exhaust  valve springs  with  dampers  should  have  a  load  of  40-46 pounds  when  compressed  to  a  length  of  2.237  inches (valve  closed)  and  a  load  of  105-115  pounds  when compressed  to  a  length  of  1.780  inches  (valve  open). Install  new  spring  when  old  spring  is  5  percent  under or   over   load   limits. (2)  Replace  intake  and  exhaust  valves  if  they  are cracked,  bent,  burned  or  stems  are  worn.  The  outer diameter  of  exhaust  valve  stem  is  0.3705  to  0.371 inch.  Bore  of  exhaust  valve  guide  is  0.3725  inch giving   stem-to-guide   clearance   of   0.0015   to   0.002 inch.   Replace   exhaust   valve   and/or   guide   if   clearance exceeds   0.0055   inch.   Outer   diameter   of   intake   valve stem  is  0.3715  to  0.372  inch.  Bore  of  intake  valve guide   is   0.3725   inch   giving   stem-to-guide   clearance of   0.0005   to   0.001   inch.   Replace   intake   valve   and/or guide   if   clearance   exceeds   0.0035   inch. (3)   Inspect   valve   seats.   Replace pitted,   or   loose. Removal   is   described if   cracked, in  para  14-77. (1)   Inspect   valve   seat   counterbores   for   clean- liness,  burrs,  and  correct  size.  (1.  655  to  1.666 inches  for  exhaust  valve,  1.809  to  1.810  inches  for intake  valve,  1.670  to  1.671  inches  for  0.  005  inch oversize  exhaust  valve  end  1.814  to  1.815  inches  for 0.005   inch   oversize   intake   valve). (2)  Depth  of  exhaust  valve  bore  is  0.4735  to 0. 4755 inch and 0. 4585 to 0. 4605 inch for intake valve. (3)  Chill  inserts  for  two  to  four  minutes  in  a dry  ice  container  or  cold  box. (4)  Place  cylinder  head  bottom  side  up  on  a bench.  Thoroughly  clean  counterbores  for  the  inserts with  compressed  air  and  start  an  insert  into  the  count- terbore   (valve   seat   side   up). (5)  Use  a  valve  seat  insert  installing  tool  and drive   insert   down   tightly   into   counterbore.   This operation  must  be  done  quickly  while  insert  is  cold. (6)   Exhaust   valve   seat   inserts   must   be   staked to  eliminate  the  possibility  of  the  insert  loosening  in its   bore. d.  Valve  Face  and  Valve  Seat  Grinding. NOTE Before   installing   either   new   valves   or   used valves,   valve   seats   in   cylinder   head   should be   inspected   for   proper   valve   seating.   If used   valves   are   to   be   reinstalled,   valve stems  should  be  cleaned  and  valve  faces ground  to  angles  of  30°  for  exhaust  and  in- take  valves.  When  refacing  valves,  remove all  evidence  of  pitting  and  grooving.  The valve  guide  should  be  cleaned  with  a  nylon brush.  If  bore  in  valve  guide  is  worn  oblong, or  if  valve  head  is  warped  relative  to  valve stem,  the  necessary  parts  must  be  replaced. When   new   valve   seat   inserts   are   installed, or  used  inserts  reseated,  refinishing  must be  done  with  a  valve  seat  grinder. (1)  The  cutting  face  of  the  stone  must  be  main- tained  at  the  correct  angle  and  in  proper  condition  by frequent   dressing   with   a   diamond   wheel   dresser.   The frequency  of  dressing  will  be  determined  by  condition of  the  seats  and  amount  of  metal  required  to  be  re- moved  during  the  grinding  operation. NOTE c.   Valve   Seat   Insert   Installation. NOTE Press   fit   of   valve   seat   inserts   must   be maintained. If   insert   bores   in   cylinder head  are  badly  worn,  bores  must  be machined   0.005   inch   larger   than   original’ bore.   Valve   seat   inserts   0.005   inch oversize   must   be   installed. By  grinding  valve  face  and  insert  seat  at slightly   different   angles,   a   fine   line   con- tact  of  the  face  and  seat  is  obtained,  thus eliminating  the  need  to  lap  the  seating  sur- faces  with  grinding  compound. (2)  The  difference  of  angles  is  usually  1/2  to 1-1/2°.   The   angle   of   the   insert   seat   is   made   greater than  that  of  the  valve  face,  so  as  to  assure  contact 14-78   Change   3