TM 5-3805-260-24 CYLINDER HEAD AND VALVE COMPONENTS CYLINDER HEAD AND VALVE COMPONENTS Check cylinder head for cracks before reconditioning. Flatness  of  the  cylinder  head  should  be  within  . 006 in.   (0.  15 mm) total, and a maximum of .  003 in. (0.    08  mm)  for  any  6  in.      (152.    4  mm)  span.      A maximum  stock  removal  of  .    010  in.      (0.    25  mm)  is permissible  when  resurfacing  the  head.      Always  check the thickness of a cylinder head before resurfacing.   The cylinder   head   may   have   been   resurfaced   before   and would not have enough stock to be resurfaced again. To    check    the    thickness    of    a    cylinder    head, measure  through  the  fuel  injection  nozzle  holes  at  each end  of  the  cylinder  head.      For  the  correct  thickness  of the cylinder head, see the topic CYLINDER HEAD in the SPECIFICATIONS. The     exhaust     valve     seats     have     replaceable inserts.   To remove,  use the 8S7170  Valve Seat Insert Puller Group. REMOVING EXHAUST VALVE SEAT INSERT Freeze the exhaust salve seat inserts or use the 8S7170  Valve  Seat  Insert  Puller  Group  to  install  inserts into  head.      Be  sure  bores  are  clean,  free  of  burrs,  and the insert has a good press fit into the bore. After  inserts  are  installed,  grind  the  seat  face  of the insert to be sure it is flat, has the correct angle, and is in   alignment   with   the   bore   in   the   valve   guide.         For specifications, see VALVE GRINDING SPECIFICATIONS CHART. NOTE:  Replace  exhaust  valve  seat  inserts  when  valve seat width or valve head-to-cylinder head face can not be machined to the correct specification. For specifications, see VALVE GRINDING SPECIFICATIONS CHART. A 2N8943 Valve  Seat  Insert  for  the  intake  valve is  available.      This  insert  can  be  used  in  the  repair  of cylinder   heads   which   have   an   intake   valve   seat   with damage.   Before, damage to an intake valve seat made replacement of the cylinder head assembly necessary. To use a 2N8943 Valve Seat Insert, the inlet port of the cylinder head must be machined  to  a  diameter  of 2.  1470 + .  0005 in.   (54.  534 ⁺ 0.  013 mm) and to a depth of .  442 + .  002 in.   (11.  23 + 0.  05 mm). To  install  a  2N8943  Valve  Seat  Insert  into  the cylinder    head,    freeze    the    insert    or    use    a    2P2343 Extractor    with    the    8S7170    Valve    Seat    Insert    Puller Group.   After an insert is installed, grind the seat face of the insert to be sure it is flat, has the correct angle, and is in   alignment   with   the   bore   in   the   valve   guide.         For specifications, see VALVE GRINDING SPECIFICATIONS CHART. Clean  valve  guides  of  all  carbon  and  oil,  using the 5P5176 Brush and a solvent. The    guides    are    cast    in    the    cylinder    heads. Check  each  salve  guide  bore  size  3/4  in.      (19.    1  mm) deep from each end.   The bore size is .  3745 + .  0005 in.  (9.  512 ⁺ 0.  013 mm) and the maximum size worn is .  3760 in.   (9.  550 mm).   Valve guides worn more than the   maximum   wear   size,   can   be   restored   to   original tolerances through knurling. Use  the  5P3536  Valve  Guide  Gauge  Group  to check the bore of the valve guides.   Special Instructions GMG02562 gives complete and detailed instructions for use of the 5P3536 Valve Guide Gauge Group. USING 5P3536 VALVE GUIDE GAUGE GROUP NOTE: If valve guide bore is larger than .  381 in.   (9.  68 mm),   knurling   may   not   restore   the   guide   to   original tolerances. The  following  procedure  can  be  used  to  knurl valve guide bores using the 5P5170 Knurling Group: 3-379