TM 5-3805-260-24 AIR INLET INLET AND EXHAUST SYSTEM RESTRICTION OF AIR INLET AND EXHAUST There   will   be   a   reduction   of   horsepower   and efficiency  of  the  engine  if  there  is  a  restriction  in  the  air inlet or exhaust system. Air flow through the air cleaner must not have a restriction   of   more   than   25   in.      (635   mm)   of      water difference in pressure. Back     pressure     from     the     exhaust     (pressure difference  measurement  between  exhaust  outlet  elbow and  atmosphere)  must  not  be  more  than  34  in.    (864 mm) of water. MEASUREMENT OF EXHAUST TEMPERATURES Use    the    lP3060    Pyrometer    Group    to    check exhaust    temperature.        Special    Instruction    Form    No. SMHS7179  is  the  tool  group  and  gives  instructions  for the test procedure. 1P3060 PYROMETER GROUP CYLINDER COMPRESSION An engine that runs rough can have a leak at valves,  or valves that need adjustment.   Run  the  en{  at  the  speed that gives rough running.  To find a cylinder that has low compression  or  does  not  have  good  ignition,    loosen  a fuel  line  nut  at  a  fuel  injection  pump.  This  will  stop  the flow of fuel to that cylinder.  Do for each cylinder until a loosened fuel line is found makes no difference in engine rough running.  Be sure to tighten each fuel line nut after the  test  before  the  next  fuel  line  nut  is  loosened.    This test can also be indication that the fuel injection is wrong, so more checking of the cylinder will be needed. An analysis of the  engine  cylinder  condition  can be done with controlled pressure air through the cylinder head.        Special    Instruction    GMG00694    explains    the procedure. 1. Remove the fuel injection nozzle. 2. Adapt an air hose to 1P5564 Adapter.  Install 1P5564 Adapter in the fuel injection nozzle opening in the cylinder head. 3. Start  crankshaft  rotation   until   the   piston   in the  cylinder being inspected is at TC on the compression   stroke.      In   this   position   the valves  of  this  cylinder  will  be  against  their seats. 4. Force   the   air   into   the   cylinder   and    then check   air   leakage.      An   air   leak   from   the exhaust  opening  is  an  indication  of  exhaust valve  leakage  and  leak  from  the  air  cleaner inlet is an indication of intake valve leakage. If  the  air  leakage  is  into  crankcase  during this  test,    the  piston  or  piston  rings  can  be the cause. VALVE CLEARANCE SETTING Check  and  adjust  valve  clearance  with  engine stopped. Valve  clearance   is   measured   with   a   thickness gauge between the top of the valve stem and the rocker arm. VALVE CLEARANCE CHECK: ENGINE STOPPED Exhaust...... .022 to .028 In.(0.56 to .71mm) Intake......... .012 to .018 in.(0.30 to 0.46mm) NOTE: When the valve lash (clearance) is checked adjustment is NOT NECESSARY if the measure is in the range given in the chart for VALVE CLEARANCE CHECK: ENGINE STOPPED.  If the measurement is outside this range,  adjustment is necessary.  See the chart for VALVE CLEARANCE SETTING ENGINE STOPPED,  and make the setting to the nominal (desired) specifications in this chart. VALVE CLEARANCE SETTING: ENGINE STOPPED Exhaust...... .025in.  (0.64  mm) Intake......... .015 in.  (0.38 mm) To  check  and  make  adjustment  to  the  valve  lash   the procedure that follows: 1.     Remove the valve covers. 2-65