TM  5-3825-226-24 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 valve 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 valve guides are cast in the cylinder heads. Check  each  valve  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: 3-377