COOLING SYSTEM - M.4 4. Remove   rust   and   scale   from   the   impeller   and visually inspect for cracks or damage.  Examine the impeller hub sealing face for excessive wear or scoring.  Renew if unserviceable. 5. Examine  the  water  seal  for  damage.    Excessive wear,   scoring   or   cracks   in   the   carbon   sealing face will necessitate renewal. 6. Inspect   the   bearings   for   pitting,   corrosion   or wear, and renew if necessary. To Re-Assemble the Water Pump 1. Press  the  rear  bearing  on  to  the  shaft,  fit  the bearing  distance  piece  and  then  press  on  the front  bearing.    When  fitting  the  bearings  to  the shaft,   ensure   that   the   shielded   face   of   each bearing   faces   outwards   towards   the   front   and rear end of the shaft. 2. Fit   the   grease   seal   retaining   plate   in   position against  the  back  face  of  the  rear  bearing.    This retaining  plate  is  "dished"  and  when  in  position, the  centre  of  the  plate  must  not  be  in  contact with the bearing. 3. Fit the felt seal and seal retainer housing so that these bear on the retaining plate. 4. Half fill the space between the two bearings with a    high    melting    point    grease    and    press    the complete  bearing  and  shaft  assembly  into  the pump   housing   from   the   front   end.      Securely position  the  retaining  circlip  in  the  recess  of  the pump  housing  immediately  forward  of  the  front bearing. 5. Fit  the  water  seal  into  the  housing  ensuring  that the  carbon  face  is  positioned  towards  the  rear. When  fitted,  the  seal  must  rest  squarely  on  its seat and not be canted in any way. 6. At this stage, the shaft should be turned by hand to  ensure  that  no  undue  resistance  to  rotation exists. 7. Fit the driving pulley key and press on the pulley making sure that no rearward axial movement of the shaft is incurred. 8. Where  ceramic  counter  face  seals  are  fitted,  fit seal   to   shaft   with   counter   face   towards   water seal  and  rubber  bonded  holder  towards  impeller face. Fig. M.5. Checking Impeller to Water Pump Body Clearance. 9. Press the impeller onto the shaft ensuring that a clearance  of  0.012/0.032  in  (0,30/0.81  mm)  is maintained  between  the  impeller  vanes  and  the pump body (see Fig. M.5). 10. Refit  the  plain  washer  and  pulley  retaining  self locking nut, tightening to a torque of 60 lbf ft (8,5 kgf m) - 84 Nm. SEA WATER PUMP (Open Circuit) Description This type of pump consists basically of a shaft, gear driven  from  the  rear  of  the  timing  case,  which  rotates within   bearings   in   a   water   tight   housing.      The   shaft transmits  the  drive  to  a  neoprene  impeller  mounted  on the other end.  This impeller is offset slightly to the water chamber  in  which  it  rotates.    The  impeller  blades,  being flexible have a trailing action when the pump is turned in the  normal  direction  of  rotation.    This  flexibility  permits the  impeller  to  operate  offset  to  the  centre  of  the  water chamber and has the action of drawing in water through the  suction  (inlet)  side  of  the  pump  in  the  large  pockets between  the  impeller  blades,  when  the  impeller  turns, the  blades  become  more  flexed  and  consequently  the volume  of  the  pockets  between  the  blades  decreases forcing  the  water  now  under  pressure  to  escape  as  the blades  uncover  the  outlet  port  on  the  pressure  side  of the pump. The pump is self priming, but it is advisable to prime it when first commencing service or after