Chapter 3—ENGINE MAINTENANCE
This is impossible if backlash, looseness, or play
exists in the control system. Continuous or inter-
mittent movement of the rack may indicate ex-
cessive looseness. Engine speed variations are also
indicative of this problem. Note that even though
these symptoms are characteristic of a loose rack,
a governor which is dirty or out of adjustment
will present similar symptoms.
Backlash in a fuel control system is generally
due to a wornout gear, rack, or control sleeve.
When you disassemble a pump or injector for
overhaul be sure to inspect all parts of the con-
trol system for signs of excessive wear. If the rack
may be moved more than a prescribed amount
without moving the plunger, find the parts that
are worn, and replace them.
Improper Calibration
When improper calibration (balance) of fuel
injector pumps or injectors occurs, there is a dif-
ference in the amount of fuel injected into each
of the cylinders. If some pumps or injectors
deliver more fuel per stroke than others, the
engine will be UNBALANCED; that is, some
cylinders will carry a greater load than others. This
condition may be detected by differences in
cylinder exhaust temperatures and firing
pressures, and by smoky exhaust from the
overloaded cylinders. Roughness in operation and
engine vibration are also indicators of an
unbalanced condition.
It is important to remember that many other
types of engine difficulties may cause engine
symptoms identical with those due to unbalance.
So when unbalance is suspected, consider first a
few of the other faults that may be present such
as poor condition of piston rings, inaccurate
exhaust pyrometers and thermocouples, mistimed
or faulty engine exhaust or inlet valves.
Improper Timing
Improper timing of a fuel system will result
in uneven operation or vibration of the engine.
Early timing may cause the engine to detonate and
lose power. Cylinders which are timed early may
show low exhaust temperatures. Late timing
usually causes overheating, high exhaust
temperatures, loss of power, and smoky exhaust.
Although, usually, improper fuel injection
timing is caused by failure to follow the manufac-
turer’s instructions for timing, there may be other
causes for the difficulty, depending upon design
of the particular systems. For example, fuel
injection time in the injection pump of a Bosch
system may get out of time because of a worn
pump camshaft. The same problem may occur
when the adjusting screw on the injector control
rack of a GM system becomes loose. Either of
these conditions will change fuel injection timing.
Faulty calibration and improper timing are
generally due to failure to follow instructions
given in the engine technical manual and the fuel
injection equipment maintenance manual. These
manuals should always be consulted and fol-
lowed whenever timing or calibration difficulties
arise.
GOVERNORS
To control an engine means to keep it run-
ning at a desired speed, either in accordance with,
or regardless of, the changes in the load carried
by the engine. The degree of control required
depends on two factors: The engine’s performance
characteristics and the type of load which it drives.
In diesel engines the speed and power output of
the engine is determined by varying the amount
of fuel that is injected into the cylinders to con-
trol combustion. There are two principal types of
governors: hydraulic and mechanical.
Hydraulic Governors
It is beyond the scope of this training manual
to list all of the possible troubles which may be
encountered with a hydraulic governor. This sec-
tion deals only with the most common ones. Poor
regulation of speed may be due to the faulty ad-
justment of the governor or to faulty action of
an engine, a generator, a synchronizing motor,
a voltage regulator, or any piece of equipment
which has a direct bearing on the operation of the
engine.
Manufacturers state that 50% of all governor
troubles are caused by dirty oil. For this reason,
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