are marked as point A. All indications point to a definite internal problem in one cylinder. No rise in lube oil consumption is indicated (point A on figure 2-15) because a slightly worn set of rings or liner probably would not cause a measurable increase in lube oil consumption. The logs should now be consulted to find the problem cylinder and initiate appropriate repairs. If   only   firing   pressures   and   exhaust temperature are low, the fuel system should be checked on the problem cylinder. The crankcase vacuum graph (figure 2-10) indicates ring, piston, or liner condition. As long as everything is normal, this curve will also be flat. A cracked piston, worn rings, or liner will increase blow-by, causing decreased crankcase vacuum. If crankcase vacuum decreases with no change in other  indicators,  the  crankcase  scavenging  system should  be  checked  for  proper  operation.  An increase in crankcase vacuum may be caused by a  clogged  intake  screen. The  exhaust  temperature  graph  (figure  2-11) indicates  general  cylinder  conditions  and  engine balance, although this item is not necessarily a definite indication of trouble itself. Any abnor- mal temperature with no accompanying change in  the  various  other  indicators  can  usually  be attributed to a faulty pyrometer. The pyrometer in question should then be carefully inspected and tested before any other inspections or adjustments are  accomplished. The  lube  oil  pressure  graph  (figure  2-12) indicates the engine bearing condition, lube oil pump condition, piping conditions, by-pass relief valve  conditions,  etc.  Lube  oil  pressure  obtained at the upper header of Fairbanks Morse opposed piston  engines  is  particularly  useful  in  monitor- ing the condition of the internal portion of the lube oil system. The  manifold  pressure  graph  (figure  2-13) indicates the condition of the scavenging system. Increasing   air   box   pressures   indicate   port clogging, while reduced air box pressures indicate some  abnormality  in  the  air  intake  systems, blower, or turbocharger. Both of these cases re- quire immediate attention. The fuel rack or governor power piston posi- tion graph (figure 2-14) indicates the general con- dition of the fuel system. Increased rack settings for  a  given  power  output  indicate  fuel  pump deterioration or a decrease in engine combustion efficiency. The lubrication oil consumption graph (figure 2-15) is for the lubricating oil consumption in gallons  per  200  hours  operation.  It  should  be noted that the values on this curve are initially very high. They decrease and then remain nearly constant  until  the  engine  is  approaching  its overhaul time. The initial high consumption is due to unseated piston rings. As rings become seated, the consumption will decrease to a normal value and remain nearly constant until the rings or liners begin to wear. Any significant increase in lube oil consumption must be carefully evaluated to deter- mine if the oil is really being consumed in the engine or is being lost because of external leaks. Too many times an engine is assumed to be at fault when lube oil is really being lost due to leakage. Review of figures 2-8 through 2-15 will also indicate other problems that are not discussed in this text. Each sample problem is marked on the various graphs at the appropriate engine hours so a study of the samples can be made. In conclusion, operational graphs show the condition of the engine. They show what is hap- pening, what needs to be done, and what has to be planned for in advance. The life expectancy of vital parts can be determined from these curves, and the parts can be renewed before they reach the point of failure. The trend analysis program must be followed closely, especially during the initial period of the program when care must be taken to ensure that the data gathered are meaningful. However, if the condition  of  any  particular  engine  indicates  that an overhaul is required to maintain it operational, this should be accomplished at the earliest possi- ble time. ENGINE   LUBE   OIL   ANALYSIS.— Spectrometric oil analysis is another valuable tool which  can  be  used  to  determine  the  extent  of accelerated  wear  in  internal  combustion  engines and other machinery which use closed lube oil or hydraulic oil systems. By the use of spectrometric oil analysis, the accelerated wear in machinery can be detected without disassembling the equipment long  before  there  is  any  other  indication  of ENGINEMAN  1  &  C 2-18