TM 10-3930-653-14&P when installed on engine.  The starting motor should also be   subjected   to   a   test   when   the   cause   of   abnormal operation  is  to  be  determined.    A  brief  outline  of  test  is given below. No-load test Connect the starting motor in series with a specified (12  volts)  battery  and  an  ammeter  capable  of  indicating 1.000 amperes. Fig. 4-168.   No-Load Test (2) DIAGNOSES OF TEST (1) Low speed with no-load and high current draw may result from the following causes. a. Tight.  dirty or worn bearings. b. Bent armature shaft or loose field probe. c. Shorted armature. Check armature further. d. A grounded armature or field: (a.)    Remove input terminal. (b.)    Raise two negative side brushes from commutator. (c.) Using a circuit tester.  place one probe onto yoke. (d.)    If  tester  indicates  continuity.    raise  the  other  two brushes  and  check  the  field  and  armature  separately  to determine whether the field or armature is grounded. (2) Failure to operate with high current draw may result from the following items. a. A grounded or open field coil: Inspect  connection  and  trace  circuit  with  a  circuit tester. b. Armature coil does not operate: Inspect  commutator  for  excessive  burning.    In  this case.    an  arc  may  occur  on  malfunctioning  commutator when motor is operated with no-load. c. Burned out commutator bar: Weak  brush  spring  tension,  broken  brush  spring, rubber bush, thrust out of mica in commutator or a loose contact   between   brush   and   commutator   would   cause burned-out commutator bar. (3) Low  current  draw  and  low  no-load  speed  Å  would cause high internal resistance due to loose connections, faulty  leads,  dirty  commutator  and  causes  listed  in  item 2-C. (3) MAGNETIC SWITCH ASSEMBLY TEST Fig. 4-169.  Magnetic Switch Assembly Test If   starting   motor   check   is   "OK,"   check   magnetic switch  assembly.    Connect  cables  between  "negative" battery     terminal     and     starting     motor     "M"     terminal, "positive" battery terminal and starting motor "S" terminal connecting  ignition  switch  in  series  as  shown  in  Fig.  7- 20. With    ignition    switch    on,    measure    the    gap    "Q" between pinion front edge and pinion stopper. 4-100