TM 10-3930-671-24 Battery 11. If the battery has been "running down" (discharging), or if engine cranking speed is low, check   the   alternator   circuit   and   battery.   See cranking test above. Tune-Up Procedures 1. Stall Test •    Stall  tests  must  be  performed   with   the parking brake applied and wheels blocked up  above  the  ground  surface  to  prevent movement. Be careful that the truck does not   move   unexpectedly   when   operating the     engine     and     converter     at     stall. Unexpected  movement  of  the  truck  could cause injury or death to personnel. •    Do  not  run  engine  and  converter  at  stall longer  than  necessary  to  take  the  rpm readings,  or  longer  than  30  seconds  at one   time.   Then,   shift   transmission   into NEUTRAL  for  15  seconds  and  run  the engine  at  one-half  speed  for  1-2  minutes to   cool   torque   converter   oil.   Excessive temperature    250°F    (120⁰C)    max    will overheat the converter and cause damage to converter, seals, and fluid. NOTE A stall test is perhaps the most important and useful test for   quickly   determining   engine   condition.   Stall   tests should  be  a  part  of  all  engine  tune-ups  and  must  be carefully  conducted  and  analyzed  to  pinpoint  specific problems. A  stall  test  must  include  RPM,  vacuum,  and  hydraulic pressure measurements to accurately diagnose specific problem areas. For this reason, stall testing is described in a separate, detailed section noted below. Engine  speed  and  vacuum  checks  with  engine  under load    are    made    to    also    determine    whether    major components   or   systems   other   than   the   engine   are causing problems. If  stall  speed  is  low,  do  not  automatically  blame  the torque   converter.   Carefully   check   engine   condition. Frequently,  an  obstruction,  e.g.,  carbon  plugging,  in  the air intake or exhaust system is the problem. First,  perform  a  stall  test  to  determine  engine  condition and    whether    engine    and    other    components    are functioning correctly. Check: 1)    Idle speed and vacuum. 2)    No-load governed speed and vacuum. 3)    Speed    and    vacuum    in    hydraulic    (tilt) bypass. 4)    Engine stall speed and vacuum. Refer  to  Section  4.7,  RPM,  Vacuum,  &  Stall  Tests,  for procedures and analysis of test results. Also see Section 2. 1, Service Specifications. 2. Idle Speed Check  engine  idle  speed  and  adjust  idle  setting  if  idle speed is not correct. Refer to Section 4.10 for Idle Adjustment. TMD27 Engine 650 rpm (600 700 rpm) Refer to Section 2.1, Service Specifications. 3. Compression Check If the stall speed reading is not in the correct range or the engine  runs  erratically,  perform  an  engine  compression check.  This  will  check  the  condition  of  the  piston  rings and engine valves. Refer to Section 4.6, Engine Cylinder Compression Test and Section 2.1, Service Specifications. 4. Valve Clearance Settings If the engine compression test indicates a valve problem, or  valve  train  is  noisy,  check  and  adjust  valve  (tappet) clearances, as necessary. Refer  to  Section  4.5,  Valve  Clearance  Adjustment  and Section 2.1, Service Specifications. 5. Cooling System NOTE •    Fan   blades   should   engage   1/3   of   the depth of the radiator shroud. •    The  fan  is  designed  as  a  "pusher-type" fan,  i.e.,  to  push  air  through  the  radiator. The  fan  blades  should  be  installed  with their curve to push air into the radiator as they   turn   in   the   direction   of   right-hand engine rotation. a.    If  there  is  an  indication  of  engine  overheating, perform a complete check of the engine cooling system. F-76