Section  XV.  CYLINDER  HEAD  AND  VALVE  OPERATING  MECHANISM 14-76.   General. a.  The  cylinder  head  is  a  one-piece  alloy  iron casting  and  is  secured  to  the  upper  part  of  the  cylin- der  block  by  heat-treated  capscrews.  Inlet  and  outlet ports  are  provide  in  the  cylinder  head  for  the  intake of  air  and  the  expulsion  of  exhaust  gases.  Cored passages  are  provided  for  the  circulation  of  coolant. Located  in  the  cylinder  head  above  each  cylinder  is an  intake  valve,  valve  guide,  valve  spring,  spring retainer  and  locks,  an  exhaust  valve,  valve  guide, valve  spring,  spring  retainer  and  locks,  a  fuel  injec- tion  nozzle,  and  two  rocker  arms.  The  top  of  the  cyl- inder  head  is  enclosed  with  a  cylinder  head  cover  and sealed  with  a  gasket. b.  The  rocker  arm  assembly,  consisting  of  two rocker  arms  for  each  cylinder,  is  mounted  on  a  com- mon  rocker  arm  shaft  supported  by  rocker  arm  shaft brackets  attached  to  the  cylinder  head.  One  rocker arm  actuates  the  Intake  valve  and  the  other  actuates the  exhaust  valve. c. The  camshaft  rotates  in  bearings  mounted  inside the-cylinder   block. It  is  mechanically  timed  with  the crankshaft  to  open  and  close  valves  at  proper  intervals. Valves  are  operated  by  caroming  action  produced  by lobes  located  along  the  length  of  the  camshaft. d.  The  push  rods  extend  down  through  the  cylinder head,  cylinder  block,  and  into  valve  lifters  which  are held  in  position  by  the  camshaft.  The  upper  end  of  the push  rods  are  concave  to  receive  the  ends  of  the  valve lash  adjustment  screws  threaded  into  one  end  of  the rocker  arms.  The  other  end  of  the  rocker  arm  actu- ates  the  valve  through  the  action  of  the  push  rod.  When the  push  rod  is  forced  upward  by  the  camshaft  lobe,  the rocker  arm  is  raised  on  one  end  and  forced  down  on  the other  end,  opening  the  valve.  The  tension  of  the  valve spring  closes  the  valve  when  the  push  rod  moves  down- ward . e.  An  oil  hole  through  the  cylinder  head  at  the flywheel  end  extends  from  the  engine  oil  gallery.  An  oil feed   tube   is   connected   from   the   cylinder   head   to   a restrictor  elbow  in  one  end  of  the  hollow  rocker  shaft. Excess  oil  is  dumped  through  an  oil  drain  tube  at  the other  end  of  the  rocket  shaft.  The  oil  feed  tube  and  drain tube   are   formed   higher   than   the   rocker   shaft   to   help force  oil  out  the  holes  in  the  rocker  shaft  through  the  oil hole  in  the  rockers,  and  keeps  the  shaft  full  of  oil  during engine  shutdown.  The  restrictor  elbow  controls  oil  flow to  the  rockers  and  prevents  excessive  pressure  drop  of the  engine  oil  pressure  system.  Oil  is  forced  out  of  the shaft   through   the   oil   hole   at   each   rocker   arm   location and   into   the   drilled   passage   of   each   rocker   arm,   pro- viding   lubrication   for   the   rocker   arm   bushing.   The   oil spills  down  at  the  front  end  over  the  push  rods  and  valve springs  and  drains  back  to  the  oil  pans. 14-77.   Removal   and   Disassembly. a.  Symptoms  and  Isolation  of  Malfunction. A mal - function  of  the  cylinder  head  assembly  or  valve- operating  component  is  usually  indicated  by  loss  of engine  power,  erratic  engine  speed,  or  heavy  black exhaust  smoke.  These  symptoms  are  a  result  of compression  losses  caused  by  a  leaky  head  gasket, cracked  cylinder  head,  burned,  valve,  bent,  worn,  or broken  push  rod,  or  a  defective  rocker  arm.  To  iso- late  the  cause  of  the  malfunction,  proceed  as  follows: (1)  Remove  the  valve  cover  and  observe  the rocker  arms  with  the  engine  running.  If  one  of  the rocker  arms  or  push  rods  has  failed,  it  can  usually be  detected  by  comparing  the  motion  of  all  the  rocker arms. (2)  One  by  one,  slightly  loosen  the  fuel  input line  to  each  injector  with  the  engine  running.  This stops fuel to the cylinder. If the engine speed and sound does  not  change  when  the  fuel  to  the  cylinder  is  reduced, a  valve  in  that  cylinder  has  probably  failed.  Tighten each  fuel  line  after  check  has  been  made.  To  verify  a valve  failure,  remove  one  at  a  time  the  fuel  injector for  each  cylinder  and  perform  compression  tests  using a  0-700  psi  gauge.  The  compression  pressure  at  sea level  with  engine  at  cranking  speed,  150  rpm  (use  dead crank switch) and hot should be 400 ±15 psi. (3)  A  leaky  head  gasket  or  a  crack  in  the  head can  usually  be  determined  by  visual  inspection.  Signs of coolant  leakage  will  be  evident  at  the  point  where the  head  mates  with  the  block  if  the  gasket  is  bad.  A crack  in  the  cylinder  head  is  usually  indicated  by  the presence  of  an  irregular  hairline  surrounded  by  signs of  coolant  leakage  or  a  black  deposit  of  exhausted carbon. (4)  If  and  of  the  above  checks  indicate  failure  of a  cylinder  head  component,  proceed  with  the  removal and   repair   procedures. b.  Cylinder  Head  and  Rocker  Arm  Shaft  Assembly Removal. (1)  Refer  to  Operator  and  Organizational  Main- tenance  Manual  to  drain  the  cooling  system,  disconnect ether   starting   aid   and   remove,   the   turbocharger,   in- take  and  exhaust  manifold,  nozzle  holder  assemblies valve  cover. 1 4 - 76 Change   5