procedure varies to some extent, depending on the valve
Except in emergencies, it is advisable to shut the
engine down when troubles cause safety valve popping.
Clogged or partially obstructed exhaust ports may
also cause the cylinder safety valve to lift. This condition
will not occur often if proper planned maintenance
procedures are followed. If it does occur, the resulting
increase in cylinder pressure may be enough to cause
safety valve popping. Clogged exhaust ports will also
cause overheating of the engine, high exhaust
temperatures, and sluggish engine operation.
You can prevent clogged cylinder ports by removing
carbon deposits at prescribed intervals. Some engine
manufacturers make special tools for port cleaning.
Round wire brushes of the proper size are satisfactory
for this work You must be careful in cleaning cylinder
ports to prevent carbon from entering the cylinder-bar
the engine to such a position that the piston blocks the
SYMPTOMS OF ENGINE TROUBLE
In learning to recognize the symptoms that may help
locate the causes of engine trouble, you will find that
experience is the best teacher. Even though written
instructions are essential for efficient troubleshooting,
the information usually given serves only as a guide. It
is very difficult to describe the sensation that you should
feel when checking the temperature of a bearing by
hand; the specific color of exhaust smoke when pistons
and rings are worn excessively; and, for some engines,
the sound that you will hear if the crankshaft
counterweights come loose. You must actually work
with the equipment to associate a particular symptom
with a particular trouble. Written information, however,
can save you a great deal of time and eliminate much
unnecessary work. Written instructions will make
detection of troubles much easier in practical situations.
A symptom that indicates that trouble exists may be
in the form of an unusual noise or instrument indication,
smoke, or excessive consumption or contamination of
the lube oil, fuel, or water. Figure 3-43 is a general listing
of various trouble symptoms that you may encounter.
The unusual noises that may indicate that trouble
exists or is impending may be classified as pounding,
knocking, clicking, and rattling. Each type of noise must
be associated with certain engine parts or systems that
might be the source of trouble.
Pounding or hammering is a mechanical knock (not
to be confused with a fuel knock). It may be caused by
a loose, excessively worn, or broken engine part. Gen-
erally, troubles of this nature will require major repairs.
Detonation (knocking) is caused by the presence of
fuel or lubricating oil in the air charge of the cylinders
during the compression stroke. Excessive pressures
accompany detonation. If detonation is occurring in one
or more cylinders, stop the engine immediately to
prevent possible damage.
Clicking noises are generally associated with an
improperly functioning valve mechanism or timing
gear. If the cylinder or valve mechanism is the source of
metallic clicking, the trouble may be due to a loose valve
stem and guide, insufficient or excessive valve tappet
clearances, a loose cam follower or guide, broken valve
springs, or a valve that is stuck open. A clicking in the
timing gear usually indicates that there are some
damaged or broken gear teeth.
Rattling noises are generally due to vibration of
loose engine parts. However, an improperly functioning
vibration damper, a failed antifriction bearing, or a
gear-type pump operating without prime are also
possible sources of rattling noises.
When you hear a noise, first make sure it is a trouble
symptom. Each diesel engine has a characteristic noise
at any specific speed and load. The noise will change
with a change in speed or load. As an operator, you must
become familiar with the normal sounds of the engine.
Investigate all abnormal sounds promptly. Knocks that
indicate a trouble may be detected and located by special
instruments or by the use of a sounding bar, such as a
solid iron screwdriver or bar.
As an engine operator, you will probably rely more
on the instruments to warn you of impending troubles
than on all the other trouble symptoms combined.
Regardless of the type of instrument being used, the
indications are of no value if the instrument is
inaccurate. Be sure an instrument is accurate and
operating properly before you accept a low or high
reading. Test all instruments at specified intervals or
whenever you suspect them of being inaccurate.