Chapter  3—ENGINE  MAINTENANCE Another  source  of  trouble  during  installation is due to the interchanging of the upper and lower shells. The installation of a plain upper shell in place  of  a  lower  shell,  which  contains  an  oil groove, completely stops the oil flow and leads to early bearing failure. The resulting damage not only may ruin the bearing but may also extend to  other  parts,  such  as  the  crankshaft  connecting rod, piston, and wrist pin. 8. Failure to follow recommended procedures in  the  care  of  lubricating  oil.  Lack  of  proper amount   of   lubricating   oil   will   cause   the overheating  of  a  bearing,  causing  its  failure  (see figure 3-22). In large engines, the volume of the lubricating oil passages is so great that the time required to fill them when starting an engine could be sufficient to permit damage to the bearings. To  prevent  this,  separately  driven  lubricating  oil priming pumps are installed, and by their action, the  oil  is  circulated  to  the  bearings  before  an engine  is  started.   Priming  pumps  should  be secured  prior  to  starting  the  engine  when  the prescribed pressure has been obtained. circulation,   and   sufficiently   low   to   prevent excessive oxidation of the lubricating oil. Nor- mally,   the   manufacturer’s   technical   manual should be followed as to the correct lubricating oil  temperature  to  maintain.  However,  if  no manual is available, the temperature of the oil leaving the engine should be maintained between 160°  and  200°F.  When  possible,  oil  must  be analyzed  at  recommended  intervals  to  determine its suitability for further use. In addition, regular service of oil filters and strainers must be main- tained, and oil samples must periodically be drawn from the lowest point in the sump to determine the presence of abrasive materials or water. The lube oil purifier should be used in accordance with required procedures. Strict adherence to recom- mended practices will reduce the failure of bear- ings and other parts because of the contaminated oil or insufficient supply of clean oil. FRICTIONLESS  BEARINGS Maintenance of recommended oil pressures is essential to ensure an adequate supply of oil at all bearing surfaces. Refer to the oil pressure gage as it is the best source of operational information to indicate satisfactory performance. Figure  3-23  lists  the  troubles  that  may  be encountered with all types of (antifriction fric- tionless)  bearings. Use  Navy-approved,  low-corrosive  lubricating oils at recommended oil temperatures. Recom- mended temperatures have been determined by extensive  tests  in  laboratory  and  in  service. They are sufficiently high to assure satisfactory Since dirty bearings will have a very short serv- ice  life,  every  possible  precaution  must  be  taken to prevent the entry of foreign matter into bear- ings. Dirt in a bearing which has been improperly or insufficiently cleaned may be detected by noise when  the  bearing  is  rotated,  by  difficulty  in rotating, or by visual inspection. Do not discard an antifriction bearing until you have definitely established that something in addition to dirt has caused the trouble. You may determine this by properly cleaning the bearing. Spalled or pitted rollers or races may be first recognized by the noisy operation of the bearing. Upon removal and after a very thorough clean- ing, the bearing will still be noisy when rotated by hand. (Never spin a frictionless bearing with compressed air.) Roughness may indicate spall- ing at one point on the raceway. Figure 3-22.—Overheated bearing. 121.6 Pay particular attention to the inner surface of the inner race, since it is here that most sur- face disintegration first occurs. Since pits may be covered with rust, any sign of rust on the rollers or  contact  surfaces  of  the  races  is  a  probable indication that the bearing is ruined. 3-35