GOVERNORS Speed Limits & Repair If a Service Replacement Engine is used, check the top governed   speed   using   a   tachometer,   with   the   engine operating on a completely assembled mower, to be sure the   blade   tip   speed   will   not   exceed   19,000   feet   per minute.    If   necessary,   change   the   governor   spring   or adjust  the  top  speed  limit  device,  so  the  engine  will  not exceed the recommended speed, based on blade length as  shown.    See  page  6  for  adjustment  procedure  for mechanical governor. If   a   governor   spring   must   be   replaced,   consult   the appropriate   Illustrated   Parts   List.      Choose   the   proper governor spring by engine type number.  AFTER A NEW GOVERNOR SPRING IS INSTALLED, CHECK ENGINE TOP     GOVERNED     SPEED     WITH     AN     ACCURATE TACHOMETER. Run  engine  at  half  throttle  to  allow  the  engine  to  reach normal  operating  temperature  before  measuring  speed with a tachometer.  To account for tolerances, which may be  required  by  tachometer  manufacturers,  we  suggest that the top governed speed of the engine be adjusted at least    200    R.P.M.    lower    than    the    maximum    speeds shown. Since  blade  tip  speed  is  a  function  of  engine  R.P.M., lower tip speeds require lower engine speeds. The chart below lists various lengths of rotary lawnmower    cutter    blades,    and    the    maximum    blade rotational speeds, which will produce blade tip speeds of 19, 000 feet per minute. BLADE MAXIMUM LENGTH ROTATIONAL R.P.M. 18" 4032 19" 3820 20" 3629 21" 3456 22" 3299 23" 3155 24" 3024 25" 2903 26" 2791 NOTE:    For  correct  no  load  R.P.M.  by  model  and  type, see engine sales manual.  Note column. MECHANICAL GOVERNOR MODELS N, 6, 8 (CAST IRON) Disassembly Loosen  the  two  mounting  screws  to  remove  governor housing.    The  cup  can  be  pulled  off  the  governor  gear and the gear will slide off the shaft. See  Fig.  4.    To  disassemble  the  governor  crank,  drive the roll pin out at the end of the governor lever; remove the  governor  crank  bushing.    Then  pull  governor  crank out of the housing. Fig. 4.  Governor Housing and Gear Assembly Re-Assembly To  assemble  the  governor  crank,  bushing  and  lever  to the housing, push the governor crank, lever end first, into the housing.  Slip the bushing onto the shaft:; then thread the bushing into the housing and tighten securely.  Place the  lever  on  the  shaft  with  the  governor  crank  in  the position  shown  in  Fig.  5.    Place  the  governor  gear  on shaft  in  cylinder.    Place   gasket   on   governor   housing; then   assemble   governor   housing   to   the   cylinder   and tighten in place with two mounting screws. Fig. 5 - Install Crank and Lever 2