ENGINEMAN  1  &  C (low speed) spring. Maximum speed control is ef- fected by the action of the high speed (small) flyweights acting against a heavy (high speed) spring. (See figure 3-16.) Mechanical  governor  faults  usually  manifest themselves  in  speed  variations;  however,  not  all speed  variations  indicate  governor  faults.  When improper   speed   variations   appear   do   the following: 1.  Check  the  load  to  be  sure  that  speed changes are not the result of load fluctuations. 2. If the load is found to be steady, check the engine to be sure all cylinders are firing properly. 3. Make sure there is no binding in the gover- nor  mechanism  or  operating  linkage  between governor and engine, and that no binding exists in  the  injector  control  rack  shaft  or  its  mounting brackets. If you find no binding anywhere and the governor still fails to control the engine prop- erly, you may assume the governor is worn or unfit for further service until the unit has been completely  disassembled,  inspected,  and  rebuilt or replaced. 121.23 Figure  3-16.—Mechanical  governor  control  mechanism. Adjustment procedures for the replacement of any  governor  are  listed  in  the  manufacturer’s instruction  manual  and  should  be  followed  with particular attention given to the precautions listed. OVERSPEED  SAFETY  DEVICES Mechanical overspeed trips depend on the cen- trifugal forces developed by the engine and should be  maintained  in  good  working  condition.  A faulty overspeed device can endanger not only the engine  but  also  personnel  if  the  engine  explodes or flies apart because of uncontrolled speed. The engine instruction manual contains infor- mation as to the speed at which the overspeed is supposed to function. Most overspeed trips are adjustable. Prior to making any change in the ad- justment of the overspeed trip, determine if the engine did not trip out for some reason other than the action of the element of the overspeed trip. It is highly advisable that you first check the ac- curacy   of   the   tachometer   and   then   test   the overspeed trip. All spring tension adjustments and linkage  adjustments  to  an  overspeed  trip  are critical. Instructions given for making these ad- justments  are  found  in  the  manufacturer’s  instruc- tions manual and must be followed. Hydraulic  overspeed  trips  are  extremely  sen- sitive to dirt. Dirt or lacquer-like deposits may cause a trip to bind internally. The speed sensitive element must be kept clean and so should all parts of the linkage and mechanisms incorporated in this  speed  sensitive  element.  When  painting around  the  engine,  the  painter  should  be  cau- tioned against allowing paint to fall on joints, springs,  pins,  and  other  critical  points  in  the linkage. All linkage binding should be eliminated. If parts  are  bent,  badly  worn,  improperly  installed, dirty, or if their motion is restricted by some other part  of  the  engine,   the  trip  will  not  function properly.  On  occasion  the  drive  shaft  of  the overspeed trip may be broken and prevent rota- tion  of  the  flyweight  and  the  overspeed  trip. Insufficient  oil  in  the  hydraulic  trip  may  be another  source  of  this  problem.  Oil  should  be maintained at the level specified in the instruc- tion manual. The cause of any malfunction should be deter- mined and eliminated. This will involve cleaning the trip and its linkage, removing the source of 3-24