are marked as point A. All indications point toa definite internal problem in one cylinder. Norise in lube oil consumption is indicated (point Aon figure 2-15) because a slightly worn set of ringsor liner probably would not cause a measurableincrease in lube oil consumption. The logs shouldnow be consulted to find the problem cylinder andinitiate appropriate repairs.If only firing pressures and exhausttemperature are low, the fuel system should bechecked on the problem cylinder.The crankcase vacuum graph (figure 2-10)indicates ring, piston, or liner condition. As longas everything is normal, this curve will also be flat.A cracked piston, worn rings, or liner will increaseblow-by, causing decreased crankcase vacuum. Ifcrankcase vacuum decreases with no change inother indicators, the crankcase scavenging systemshould be checked for proper operation. Anincrease in crankcase vacuum may be caused bya clogged intake screen.The exhaust temperature graph (figure 2-11)indicates general cylinder conditions and enginebalance, although this item is not necessarily adefinite indication of trouble itself. Any abnor-mal temperature with no accompanying changein the various other indicators can usually beattributed to a faulty pyrometer. The pyrometerin question should then be carefully inspected andtested before any other inspections or adjustmentsare accomplished.The lube oil pressure graph (figure 2-12)indicates the engine bearing condition, lube oilpump condition, piping conditions, by-pass reliefvalve conditions, etc. Lube oil pressure obtainedat the upper header of Fairbanks Morse opposedpiston engines is particularly useful in monitor-ing the condition of the internal portion of thelube oil system.The manifold pressure graph (figure 2-13)indicates the condition of the scavenging system.Increasing air box pressures indicate portclogging, while reduced air box pressures indicatesome 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 settingsfor a given power output indicate fuel pumpdeterioration or a decrease in engine combustionefficiency.The lubrication oil consumption graph (figure2-15) is for the lubricating oil consumption ingallons per 200 hours operation. It should benoted that the values on this curve are initiallyvery high. They decrease and then remain nearlyconstant until the engine is approaching itsoverhaul time. The initial high consumption is dueto unseated piston rings. As rings become seated,the consumption will decrease to a normal valueand remain nearly constant until the rings or linersbegin to wear. Any significant increase in lube oilconsumption must be carefully evaluated to deter-mine if the oil is really being consumed in theengine or is being lost because of external leaks.Too many times an engine is assumed to be atfault when lube oil is really being lost due toleakage.Review of figures 2-8 through 2-15 will alsoindicate other problems that are not discussed inthis text. Each sample problem is marked on thevarious graphs at the appropriate engine hours soa study of the samples can be made.In conclusion, operational graphs show thecondition of the engine. They show what is hap-pening, what needs to be done, and what has tobe planned for in advance. The life expectancyof vital parts can be determined from these curves,and the parts can be renewed before they reachthe point of failure.The trend analysis program must be followedclosely, especially during the initial period of theprogram when care must be taken to ensure thatthe data gathered are meaningful. However, if thecondition of any particular engine indicates thatan 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 toolwhich can be used to determine the extent ofaccelerated wear in internal combustion enginesand other machinery which use closed lube oil orhydraulic oil systems. By the use of spectrometricoil analysis, the accelerated wear in machinery canbe detected without disassembling the equipmentlong before there is any other indication ofENGINEMAN 1 & C2-18
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