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
