TM 10-3930-653-14&P 4-7-3-2. OPERATION When the ignition switch is turned fully clockwise to the    START    position,    battery    current    flows    through "series"  and  "shunt"  coils  of  the  solenoid,  magnetizing the solenoid.  The plunger is pulled into the solenoid so that  it  operates  the  shift  lever  to  move  the  drive  pinion into  the  flywheel  ring  gear.    Then  the  solenoid  switch contacts close after the drive pinion  is  partially  engaged with the ring gear. Closing  of  the  solenoid  switch  contacts  causes  the motor  to  crank  the  engine  and  also  cut  out  the  "series" coil of the solenoid, the magnetic pull of the "shunt" coil being   sufficient   to   hold   the   pinion   in   mesh   after   the shifting has been performed. After  the  engine  starts  running,  the  driver  releases the  ignition  key  and  it  automatically  returns  to  the  ON position. This   breaks   the   solenoid   circuit   so   that   reverse current  flows  through  the  series  coil,  and  the  magnetic field builds up in the direction in which the plunger moves back.      As   this   happens,   the   resultant   force   of   the magnetic   fields   in   the   shunt   coil   and   the   series   coil becomes zero.  The return spring then actuates the shift lever  which  pulls  the  plunger,  and  allows  it  to  open  the solenoid   switch   contacts.      Consequently,   the   starting motor stops. Fig. 4-152.  Starting Motor Circuit More positive meshing and demeshing of the pinion and the ring gear teeth is caused by means of the over- run clutch.  The over-run clutch  employs  a  shift  lever  to slide  the  pinion  along  the  armature  shaft,  into  or  out  of mesh  with  the  ring  gear  teeth.    The  over-run  clutch  is designed    to    transmit    driving    torque    from    the    motor armature  to  the  ring  gear,  but  permit  the  pinion  to  over run the armature after the engine has started. 4-94