CYLINDER HEAD—E.4 Hand Grinding The efficiency of a diesel engine depends largely on the maintenance    of    good    compression,    therefore    when grinding  in  valves,  make  certain  that  no  signs  of  pitting are  left  on  the  seatings.    At  the  same  time  care  should be   taken   to   avoid   unnecessary   grinding   away   of   the valve seat. 1. With   the   valve   removed   apply   a   thin   coating   of medium   or   fine   grinding   paste   according   to   the surface  condition  of  the  seat  and  replace  the  valve in its guide. 2. Lightly rotate the valve using a suitable suction tool in   alternate   directions,   raising   the   valve   from   its seat from time to time and turning it continuously to ensure a concentric seat. 3. Add more grinding paste if necessary and continue the   operation   until   an   even   grey   matt   finish   is obtained. 4. After   grinding   operations   have   been   completed. check the valve head depths relative to the cylinder head    face    to    ensure    that    they    are    within    the specified limit below the head face (see Page B.7). 5. Thoroughly     wash     off     the     cylinder     head     with cleaning  fluid  and  ensure  that  all  traces  of  grinding paste have been removed. Valve Seat Inserts Valve   scat   inserts   are   not   fitted   to   4.236   marine engines  during  production.    It  is,  however.    permissible to   fit   inserts   to   valve   seats   where   it   is   considered necessary, i.e.  if the existing seat is damaged or worn to such  an  extent  that  recutting  and  lapping  would  place the valve depth relative to the cylinder head face beyond the maxi mum limits as given on Page B.7. When fitting inserts ensure that genuine Perkins Parts are used. 1. Using  the  appropriate  size  piloted  reamer  0.015  in (0,38  mm),  or  0.030  in  (0,76  mm)  according  to  the condition  of  the  valve  bores  in  the  cylinder  head- ream out the valve bores. NOTE It    is    well    to    remember    that    the appropriate oversize stem replacement   valves   will   be   needed when this operation has been carried out on guideless cylinder heads. Fig. E.6. Valve Seat Cutting Dimensions. Inlet A.—0.283/0.288 in (7,19/7,31 mm) B.—2.0165/2.0175 in (51,22/51,24 mm) C —Radius 0.015 in (0,38 mm) max Exhaust A.—375 to .380 in B.—1.678 to 1.679 in C.—Radius 015 in (max.) 2. Using  the  new  valve  bore  as  a  pilot,  machine  the recess  in  the  cylinder  head  face  to  the  dimensions shown in Fig. E.6. 3. Remove  all  machining  swarf  and  thoroughly  clean the insert recess (removing any burrs which may be present),  and  once  more  using  the  valve  bore  as  a pilot,  press  the  insert  home  using  the  inserting  tool (see Fig. E.7) using a steady pressure with either a hand or hydraulic press. This  tool  will  ensure  squareness  which  is  essential whilst the insert is being pressed home. The  insert  must  not,  under  any  circumstances.    be hammered   in,   neither   should   any   lubrication   be used. 4. Visually  inspect  to  ensure  that  the  insert  has  been pressed  fully  home,  i.e.    is  flush  with  the  bottom  of the recess. 5. Once    again    using    the    valve    bore    as    a    pilot, machine   the   "flare"   to   the   dimensions   given   in Fig. E.8. 6. Remove  all  machining  swarf  and  any  burrs  which may be present.