TM 1-1500-204-23-1 (e) Cylinders with below minimum compression.        Engines    having    cylinders    with    below minimum  required  compression  will  be  processed  using the following procedures. 1 Remove    rocker    box    covers    on cylinders with low compression. 2 Turn   crankshaft   until   piston   is   on top  dead  center  of  compression  stroke  and  check  intake and exhaust valves for clearance. 3 When valves are held open due to negative clearance, adjust valves to proper clearance. 4 Check  for  excessive  leakage  past piston by squirting engine oil into cylinder, pulling engine through compression stroke, and then checking compression. 5 Continue     cylinder     In     service     if compression Is up to required minimum. (f) Cold  cylinder  check.    The  tendency for any cylinders to be cold or only slightly warm indicates lack  of  combustion  or  incomplete  combustion  within  the cylinder.      Perform   this   check   using   an   approved   cold cylinder indicator. 1 Head aircraft into wind to minimize irregular cooling of Individual cylinders. 2 Open cowl flaps. NOTE Do  not  close  cowl  flaps  under  any circumstances,  as  the  resulting  heat will affect the readings obtained and overheat the ignition leads. 3 Start    engine.        After    engine    is running, place ignition switch to position where excessive rpm drop is obtained.  In cases where an excessive rpm drop has occurred on both magnetos, or where excessive manifold  pressure  is  obtained  at  a  given  rpm,  perform check twice, once on LEFT and once on RIGHT position. 4 Operate  engine  at  roughest  speed between  1200  and  1600  rpm  or  at  rpm  up  to  Ignition check speed until a cylinder head temperature reading of   302   to   338°F   (150   to   170°C)   is   obtained   or   until temperature stabilizes at a lower reading. NOTE In cases where engine roughness is encountered     at     more     than     one speed, or there is an indication that a  cylinder  ceases  to  operate  at  idle speed  or  higher  speeds,  it  will  be desirable  to  run  engine  at  each  of these   speeds   and   perform   a   cold cylinder  check  to  pick  out  all  dead or intermittently operating cylinders. In    cases    where    lower    output    or engine  vibration  is  encountered  at speeds     above     1600     rpm,     when operating   with   ignition   switch   on BOTH,  engine  should  be  run  at  the speed where the difficulty Is encountered     until     cylinder     head temperature   reaches   302   to   338 °F (150  to  170C),  or  until  temperature has stabilized at a lower value. 5 Stop    engine    by    moving    mixture control  to  IDLE  CUT-OFF  position  When  engine  ceases firing,    turn    off    both    individual    and    master    Ignition switches. 6 Measure and record relative temperatures  of  each  cylinder,  starting  with  any  cylinder and   proceeding   In   numerical   order   around   engine,   by pressing tip of Indicator pickup rod of cold cylinder tester against each cylinder. NOTE It   is   essential   that   a   firm   contact   be made  at  the  same  relative  location  on each cylinder in order to obtain temperature   value      This   measurement must    be    performed    in    the    shortest possible time after engine ceases firing. 7 Recheck   cylinders   that   have   low values   and   two   cylinders   having   highest   readings   to determine amount of cooling during check. 8 Compare temperature readings obtained  In  order  to  determine  which  cylinders  are  dead or operating intermittently. 7-12