TM 10-3930-671-24 Cleaning Combustion Pocket Clean  and  insert  combustion  pocket.    Inspect  carefully for cracks. 4. Remove all carbon from combustion areas using scraper and wire brush. 5. Clean the cylinder head thoroughly with a solvent or  degreasing  solution  and  blow  it  off  with  air pressure.  Inspect carefully for cracks. VALVE GUIDES 1. Clean  the  valve  stem  guides,  removing  lacquer or other deposits.  Do not use tools that remove metal. 2. Check   guides   for   wear   by   using   a   telescope gauge  and  1"  micrometer.    Replace  all  guides that  are  worn  bell-mouthed  or  have  increased .0015"  (0.038mm)  in  diameter.    See  Limits  and Clearance Section for maximum diameter permissible  to  determine  actual  amount  it  has increased.        Remove    all    valve    guides    when necessary    by    pressing    them    out    from    the combustion chamber side. 3. Replace worn guides as required by pressing  in new  guides  to  the  correct  depth  as  given  in  the Valve Guide Data figure on the following page. CAUTION When  replacing  guides  do  not  ream since these are all pre-reamed before being ferrox coated-any further reaming  will  remove  the  coating  and damage guides. VALVE SEAT INSERTS (IF SUPPLIED) 1. The exhaust valve seat insert is held in place by a shrink fit. Inspect all exhaust valve inserts in the head and replace any that are loose, cracked or other wise damaged.  Use puller for removing faulty insert. 2. When required to replace with new insert, clean and counterbore for .010" (0.25mm) larger insert using  counterbore  tool  with  correct  fitting  pilot. When machining the counterbore, be sure to go deep enough with the tool to clean up the bottom so  that  the  insert  will  have  full  contact  to  carry away the heat. Continental  does  not  recommend  installing  new inserts having the same outside diameter as the one removed. New   insert   installation   must   have   a   press   fit. Chill   insert   in   container    with    dry    ice    for    20 minutes before assembling. Insert  may  then  be  installed  in  the  counterbore using  a  piloted  driver  and  arbor  press,  without the  possibility  of  shearing  the  side  walls.    This assures  it  being  seated  firmly  on  the  bottom  of the counterbore. 3. Grind  the  intake  and  exhaust  valve  seats  in  the head in accordance with instructions in the Valve Guide  Data  figure.    Before  removing  the  arbor, indicate  the  seat.    Total  indicator  reading  of  the runout must not be more  than  .002"  (0.05mm)  . Use a pilot having a solid stem with a long taper, as all valve seats must be ground concentric and square with either new or worn valve stem guide holes. F-169