learning to recognize and locate engine troubles,
experience is the best teacher.
Instruments play an important part in detecting
engine troubles. You should read the instruments and
record their indications regularly. If the recorded
indications vary radically from those specified by
engine operating instructions, the engine is not
operating properly and some type of corrective action
must be taken. You must be familiar with the
specifications in the engine operating instructions,
especially those pertaining to temperatures, pressures,
and speeds. You should know the probable effect on the
engine when instrument indications vary considerably
from the specified values. When variations occur in
instrument indications, before taking any corrective
action be sure the instruments are not at fault before you
try corrective actions on the engine. Check the
instruments immediately if you suspect them of being
inaccurate.
Periodic inspections are also important in detecting
engine troubles. Such inspections will reveal the failure
of visible parts, presence of smoke, or leakage of oil,
fuel, or water. Cleanliness is probably one of the greatest
aids in detecting leakage.
When you secure an engine because of trouble, your
procedure for repairing the casualty should follow an
established pattern, if you have diagnosed the trouble.
If you do not know the location of the trouble, find it.
To inspect every part of an engine whenever trouble
occurs would be an almost endless task. You can find
the cause of the trouble much more quickly by following
a systematic and logical method of inspection,
Genernlly speaking, a well-trained troubleshooter can
isolate the trouble by identifying it with one of the
engine systems. Once you have associated the trouble
with a particular system, the next step is to trace out the
system until you find the cause of the trouble. Troubles
generally originate in only one system, but remember
that troubles in one system may cause damage to another
system or to basic engine parts. When a casualty
involves more than one system of the engine, trace each
system separately and make corrections as necessary. It
is obvious that you must know the construction,
function, and operation of the various systems as well
as the parts of each system for a specific engine before
you can satisfactorily locate and remedy troubles.
Even though there are many troubles that may affect
the operation of a diesel engine, satisfactory
performance depends primarily on sufficiently high
compression pressure and injection of the right amount
of fuel at the proper time. Proper compression depends
basically on the pistons, piston rings, and valve gear,
while the right amount of fuel obviously depends on the
fuel injectors and their actuating mechanism. Such
troubles as lack of engine power, unusual or erratic
operation, and excessive vibration may be caused by
either insufficient compression or faulty injector action.
You can avoid many troubles by following the
prescribed instructions for starting and operating the
engine, The troubles discussed in the following sections
do not comprise a complete list, nor do they all
necessarily apply to all diesel engines because of
differences in design. Specific information on
troubleshooting for all the diesel engines used by the
Navy would require more space than is available here.
Even though a successful troubleshooter generally
associates certain troubles with a particular system or
assembly, the following sections discuss troubles
according to when they might be encountered, either
before or after the engine starts.
ENGINE FAILS TO START
In general, the troubles that prevent an engine from
starting are (1) the engine can neither be cranked nor
barred over, (2) the engine cannot be cranked, but it can
be barred over, and (3) the engine can be cranked, but it
still fails to start. Figure 3-36 illustrates various
conditions that commonly cause difficulties in cranking,
jacking over, or starting the engine.
Engine Cannot Be Cranked nor Barred Over
Most prestarting instructions for large engines
require you to turn the crankshaft one or more
revolutions before applying starting power. If you
cannot turn the crankshaft over, check the turning gear
to be sure it is properly engaged. If the turning gear is
properly engaged and the crankshaft still fails to turn
over, check to see whether the cylinder test valves or
indicator valves are closed and are holding water or oil
in the cylinder. When the turning gear operates properly
and the cylinder test valves are open but the engine still
cannot be cranked or barred over, check for a serious
problem. A piston or other part may be seized or a
bearing may be fitting too tightly. Sometimes you may
need to remove a part of an assembly to remedy the
difficulty.
3-23