TM 5-3825-226-24 AIR 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    1P3060    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 the valves, or valves that need adjustment.  Run the engine at the speed that gives rough running.  To find a cylinder that  has  low  compression  or  does  not  have  good  fuel ignition,  loosen  a  fuel  line  nut  at  a  fuel  injection  pump. This will stop the flow of fuel to that cylinder.  Do this for each   cylinder   until   a   loosened   fuel   line   is   found   that 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  an  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 lP5564 Adapter.  Install the 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 for air leakage.  An air leak from the exhaust opening is an indication of exhaust valve leakage and an air leak from the air cleaner inlet is an indication of intake valve leakage.  If the air leakage is into the 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 0.71 mm) Intake   ......................................................012 to .018 in.  (0.30 to 0.46 mm) NOTE: When the valve lash (clearance)  is  checked,  adjustment  is NOT  NECESSARY  if  the  measurement 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   ...................................................025 in. (0.64 mm) Intake   ......................................................015 in. (0.38 mm) To check and make adjustment to the valve lash, use the procedure that follows: 1. Remove the valve covers. 2-65