Section XII. OIL PUMP AND OIL PAN ASSEMBLY 14-64.   General. The  gear-type  oil  pump  is  mounted  on  the front  of  the  cylinder  block  and  the  drive  gear  meshes with   the   crankshaft   gear. b.  A  reIief  valve,  located  in  the  oil  pump  out- let,  bypasses  oil  back  to  the  oil  pan  when  the  press- ure   exceeds   82   to   98   psi.   This   relieves   excessive discharge  pressure  when  starting  a  cold  engine  and cuts  down  wear  on  the  oil  pump  gears. c. The  oil  pan  serves  as  a  bottom  cover  for the   crankshaft   and   a   reservoir   for   the   lubricating oil.  A  finned  steel  tube  is  installed  in  the  oil  pan. Heated  coolant  is  circulated  through  the  tube  to  pre- heat  the  oil  to  aid  in  engine  starting  in  sub-freezing temperatures. 14-65.  Removal  and  Disassembly. a. Symptoms  and  Isolation  of  Malfunction.  A malfunction  of  the  oil  pump  or  a  leak  in  the oil pump is  usually  indicated  by  10SS  of  oil  pressure  which  re- sults  in  engine  shutdown. To  isolate  the  malfunction, proceed   as   follows (1)  Examine  the  oil  pan  for  evidence  of leakage.  Leaking  oil  can  be  detected  on  top  of  the fuel  tank  located  directly  below  the  oil  pan. (2)   Check   the   oiI   Ievel   If   the   level   iS  suff- cient  for  normal  operation,  and  engine  has  shut-down due  to  loss  of  oil  pressure,  the  malfunction  is  prob- ably  the  result  of  oil  pump  failure.  Isolate  oil  pump failure  as  follows: (a)  Remove  valve  cover.  Refer  to  TM 5-6115-545-12   and   start   engine.   Before   releasing start  switch  move  the  battle  short  switch  to  the  ON position  to  by-pass  the  low  oil  pressure  cut-out  switch. (b)   If   there   is   sufficient   pressure   from the  oil  pump,  Gil  should  be  forced  out  of  the  rocker arm  shaft  above  each  cylinder.  If  there  is  no  evi- dence  of  oil  flow  at  these  points,  the  oil  pump  has failed.  Stop  the  engine  and  proceed  with  the  removal and  repair  procedures. b.   Removal   and   Disassembly. (1)  Drain  fuel  system  and  remove  main  fuel (2)   Remove   electric   starter,   tool   box   and fuel-burning  heater  if  installed.  Refer  to  Operator and   Organizational   Maintenance   Manual (3)  Open  oil  pan  drain  valve  and  allow  oil to   drain. (4)  Close  valves  for  coolant  inlet  and  outlet to   the   engine   block   if   a   winterization   kit   is installed. (5)  Disconnect  coolant  inlet  and  outlet  lines to  oil  pan  heater  element  if  winterization  kit  is  installed. Refer to TM 5-6115-545-12 for winterization kit. (6)   Disconnect   oil   drain   hose. (7)   Refer   to   figure   14-30   and   remove   and disassemble  the  oil  pan  and  heater  as  follows (a)  Remove  32  capscrews  and  lock- washers  securing  the  oil  pan  to  the  flywheel  housing, timing   gear   cover,   and   the   cylinder   block (b)  Jar  the  oil  pan  loose,  drop  the  rear end,  and  remove  pan. (c)  Remove  the  brass  fittings  from  the inside  and  Outside  of  the  connections  on  the  oil  pan. (d)   Remove   the   nuts,   lockwashers,   and capscrews   securing   the   heater   element   clamps   to the  inside  of  the  oil  pan. Remove   the   heater   element (8)  See  figures  14-31  and  14-32  and  re- move  and  disassemble  the  oil  pump  as  follows: (a)  Remove  the  clamp  supporting  the oil  suction  tube. (b)   Uncouple   the   brass   compression fitting  securing  the  oil  pump  discharge  tube. (c)  Remove  the  bolts  securing  the  oil pump  to  the  cylinder  block  and  remove  the  oil  pump assembly.  The  pump  may  have  to  be  pried  off  its mounting  dowels. (d)  Remove  the  oil  pump  suction  tube support  bracket  from  the  main  bearing  cap. (e)  Wash  the  oil  pump  assembly  in cleaning   solvent,   Federal   Specification   P-D-680. (f)  Remove  the  suction  tube  assembly. (g)   Remove   the   pressure   relief   valve assembly  from  the  pump  body. (h)  Depress  the  relief  valve  spring  and retainer   with   two   screwdrivers   or   on   improvised two-prong   tool. Drive  out  the  roll  pin  and  remove retainer,   spring   and   relief   valve   piston. (i)  Remove  the  oil  pump  drive  gear from   the   drive–shaft.   Use   a   three-leg   puller   to avoid  damage  to  the  gear. (j)   Remove   the   screws   and   washers securing  the  pump  cover  to  the  body  assembly  and remove  the  pump  cover. (k)  Remove  the  pump  driver  gear  and Change 6 14-65 tank.