binding,  replacing  faulty  parts,  adding  oil  to hydraulic type trips, or adjusting the speed sen- sitive element, always in accordance with the in- struction manual. If the trip has been damaged, it is advisable to install a spare overspeed trip and completely rebuild or overhaul the damaged one. REPAIR OF INTERNAL COMBUSTION   ENGINES The  Navy  uses  so  many  models  of  diesel engines that it is not possible to describe in any detail  all  the  overhaul  procedures  used  by  the Navy. Detailed repair procedures are listed in the manufacturers’  technical  manuals  and  in  your PMS.  Always  consult  the  manuals  and  the maintenance requirement cards (MRCs) before starting any type of repair work. Pay particular attention to installation tolerances, wear limits, adjustments,  and  safety  procedures.  Also  be  sure to follow the general rules, listed below, which apply to all engines. 1. Observe the highest degree of cleanliness in handling engine parts. Engines have been com- pletely wrecked by the presence of abrasives and various objects which have been carelessly left in the engines after overhaul. Make sure that any engine   assembled   for   post-repair   running   is scrupulously free of foreign matter prior to run- ning. Too much emphasis cannot be given to the necessity  for  maintaining  engines  clean  both  in- ternally and externally. Since dirt entering the engine  during  overhaul  causes  increased  wear  and poor operation, it is essential that all repair work be done under clean conditions. When overhaul or  repair  of  precision  parts  and  surfaces  is  re- quired,  the  parts  and  the  surface  should  be thoroughly cleaned and wrapped in a clean cloth or suitable paper. The parts should then be stored in a dry place until reinstalled. During installa- tion, parts should be wiped with a cloth free of lint  and  coated,  where  applicable,  with  clean lubricating oil. When removing or installing parts such  as  pistons,  connecting  rods,  camshafts,  and cylinder liners, make sure that these parts are not nicked or distorted. Take precautions to keep dirt and  other  foreign  material  in  the  surrounding atmosphere from entering the engine while it is being overhauled. As an example, during shipyard overhaul  periods  the  engine  should  be  protected when  sandblasting  is  occurring  in  areas  adjacent to the ship. 2. Before starting repair work, make sure that all required tools and spare parts are available. Plan  ahead  for  repair  periods  so  everything needed is available to ensure successful and ex- peditious completion of the work. WARNING Never attempt to jack the engine over by hand without first disabling the starter circuit. 3. Disable the starter circuit and tagout the starter before you start working, particularly when the jacking gear is to be engaged. 4. Keep detailed records of repairs, including measurements of worn parts (with hours in use), and the new parts installed. Later, an analysis of these records will indicate the number of hours of  operation  that  may  be  expected  from  the various parts and will facilitate prediction as to when they should be renewed before a failure occurs. Measurement of new parts are needed to determine whether or not they come within the tolerances listed in the manufacturers’ instruction books or the wear limit charts. In addition, before installation, all replacement parts should be com- pared with removed parts to ensure that they are suitable. 5. Do not test an overhauled diesel engine at 125% of full load or any other overload before the  engine  is  returned  to  service.  It  has  been reported  that  some  overhauled  diesel  engines used for driving generators are being tested at 125% of full load before being returned to serv- ice.  The  original  purpose  for  this  test  was  to demonstrate  a  25%  overload  capability  for  a 2-hour  period  to  absorb  occasional  electrical  peak loads. The nameplate rating of many of the older generator sets indicates a 25% temporary overload capacity. (More recent generator sets have a single rating  with  no  stated  overload  requirement.)  The earlier  practice  was  a  reasonable  approach  since the engine was frequently capable of substanti- ally greater power than could be absorbed by the generator and the 125% test was not likely to be detrimental to the engine. Now that these engines have aged, the margin of excess power available Chapter  3—ENGINE  MAINTENANCE 3-25