ELECTRICAL EQUIPMENT—Q.15 9. Unhook  the  plunger  spring  (14)  from  the  sliding plunger (11). 10. Take  off  the  moving  contact  plate,  remove  the contact spring (42). 11. Remove  both  solenoid  and  main  terminals  (46) and (47) from the end-shield. 12. Unscrew    the    three    solenoid    end-plate    fixing screws    (49),    (53)    and    (56).        Take    out    the endplate (43) complete with the solenoid housing.    If  the  plate  offers  resistance,  screw  in two  2BA  screws,  (approx.    2  in  (50  mm)  long) one  into  the  trip  gear  fixing  hole,  the  other  into the  stop-plate  fixing  hole.    The  end  plate  may then be easily extracted. Under no circumstances should the solenoid windings and resistor assembly be disturbed or any damage done to the mica housing. REPAIR AND TESTING INSTRUCTIONS COMMUTATOR Examine  commutator  for  wear  which,  if  not  severely pitted  or  grooved  can  be  cleaned  up  with  fine  glass  or carborundum   paper   (do   not   use   emery   cloth),   whilst spun  in  a  lathe.    If  however,  the  commutator  is  badly worn  it  should  be  skimmed,  taking  a  very  light  cut,  if possible with a diamond tool to provide the desired high quality finish. The    commutator    insulating    segments    must    not    be undercut. ARMATURE COILS The    respective    armature    coils    can    be    tested    for continuity   or   short   circuits   by   mounting   the   armature between  centres  and  connecting  the  commutator  to  an ordinary   battery   through   the   medium   of   two   brass   or copper   brushes   mounted   at   an   angle   of   90°   to   each other.      Contact   is   then   made   to   any   two   adjacent commutator   bars   by   means   of   hand   spikes   which   are connected direct to a milli-volt meter. A variable resistance should be included in the battery circuit  capable  of  carrying  the  full  output  of  the  battery and  adjusted  to  give  2  volts  or  less  on  the  armature. The armature is then rotated until every commutator bar has  been  tested,  the  reading  on  the  milli-volt  meter  in each case should read approximately the same; any big variation, indicating   a   fault   in   the   coil   connected   to   one   of   the commutator bars under test.  A reduction in the milli-volt reading   will   be   generally   found   due   to   a   short   circuit while  an  increased  reading  will  indicate  either  an  open circuit or a faulty connection. In the event of an armature being found to be faulty, it should be returned direct to a C.A.V. Agent. ARMATURE SHAFT Examine  the  elliptical  recesses  in  the  armature  shaft for burrs caused by the steel balls and carefully file these off.  Finally inspect the helices for any signs of damage. Thoroughly clean with a suitable cleaning fluid and lightly oil using Cal tex Thuben 90 or SAE 90 oil. FIELD COILS These can be simply  tested  when  in  position  for  short circuits to the yoke and poles by means (of hand spikes connected to a mains supply and in series with a lamp of suitable    voltage    positioned    on    the    live    side    of    the system.    One  spike  should  be  applied  to  the  end  of  the winding and the other to the yoke.  If the lamp does not light  then  insulation  is  intact.    Take  care  to  remove  all other connections to the coils and insulate bare ends. There  is  no  easy  way  of  testing  internal  shorts  in  the coils as the resistance is very low ; new coils should be tried if existing ones are suspect. BEARINGS If   either   the   commutator   or   drive   end   bearings   are worn and need replacing, proceed as follows: (a) Commutator End Bearing 1. Press the old bearing bush out of the end shield. 2. Press  the  new  bearing  into  the  end  shield  by using   a   stepped   highly   polished   mandrel.     A special  fitting  pin,  with  a  dimension  of  0.6263  in 0.0002 in (15,908 0,005 mm), is supplied by the makers.      After   assembly,   the   bore   should   be within the limits 0.6258 in to 0.6268 in (15,895 to 15,921    mm).        No    machining    should    be attempted. Note— Before  fitting  a  new  bearing  bush  it should   be   completely   immersed   for 24 hours in clean thin engine oil.