The gases burn the valve and seat and may cause a leak
between these two surfaces even though the original
causes of the sticking are eliminated.
Completely disassemble and inspect a leaking
valve. It is subject to a resinous deposit similar to that
found in a pressure-actuated air valve. Use a specified
cleaning compound to remove the deposit. Be sure the
valve stem is not bent. Check the valve and valve seat
surfaces carefully. Eliminate scoring or discoloration by
lapping with a fine lapping compound. You may use
jewelers rouge or talcum powder with fuel oil for
From the preceding discussion, you have learned
that the air starting system may be the source of many
troubles that will prevent an engine from cranking even
though it can be barred over. You will avoid a few of
these troubles by following prestarting and starting
instructions. One such instruction, sometimes
overlooked, is that of opening the valve in the air line.
Obviously, with this valve closed the engine will not
crank. Recheck the instructions for such oversights as a
closed valve, an empty air storage receiver, or an
engaged jacking gear before starting any disassembly.
ELECTRIC START MALFUNCTION
Electric starting system malfunctions fall into the
1. Nothing happens when the starter switch is
2. The starter motor runs, but it does not engage the
3. The starter motor engages, but it cannot turn the
If nothing happens when you close the starter
switch, there is a failure in the electrical system. The
failure could be an open circuit caused by broken
connections or burned out components. Test the circuit
continuity to make sure the relay closes and the battery
provides sufficient voltage and current to the starter
circuit. If the circuit is complete, there may be resistance
through faulty battery connections. Considerable
current is needed to operate the solenoid and starter
If the starter runs without engaging, it will produce
a distinctive hum or whine. The lack of engagement is
usually caused by dirt or corrosion, which keeps the
solenoid or Bendix gears from operating properly.
If the starter motor engages the flywheel ring gear
but is not able to turn the engine or cannot turn it quickly
enough to obtain starting speed, the cause may be lack
of battery power or, more likely, a mechanical problem.
If the engine can be barred over, there is excessive
friction in the meshing of the starter pinion and the ring
gear. Either the teeth are burred, or the starter pinion is
out of alignment. Either case would have been preceded
by noise the last time the starter was used. A major repair
may be necessary.
Other problems and malfunctions of electric
starting systems are discussed in association with
gasoline engines at the end of this chapter.
ENGINE CRANKS BUT FAILS TO START
Even when the starting equipment is in an operating
condition, an engine may fail to start. Most troubles that
prevent an engine from starting are associated with fuel
and the fuel system. However, defective or inoperative
parts or assemblies may be the source of some trouble.
Failure to follow instructions may be the cause of an
engine failing to start. The corrective action is obvious
for such items as leaving the fuel throttle in the OFF
position and leaving the cylinder indicator valves open.
If an engine fails to start, follow the prescribed starting
instructions and recheck the procedure.
Foreign Matter in the Fuel Oil System
In the operation of an internal-combustion engine,
cleanliness is of paramount importance. This is
especially true in the handling and care of diesel fuel oil.
Impurities are the prime source of fuel pump and
injection system troubles. Sediment and water cause
wear, gumming, corrosion, and rust in a fuel system.
Even though fuel oil is generally delivered clean from
the refinery, handling and transferring increase the
chances that fuel oil will become contaminated.
Corrosion often leads to replacement or at least to
repair of the part. You must continually take steps to
prevent water from accumulating in a fuel system, not
only to eliminate the cause of corrosion but also to
ensure proper combustion in the cylinders. Centrifuge
all fuel, and drain the fuel filter cases periodically to
prevent excessive collection of water.
Water in fuel will cause irreparable damage to the
entire fuel system in a short time. It corrodes the fuel
injection pump, where close clearances must be
maintained, and also corrodes and erodes the injection
nozzles. The slightest corrosion can cause a fuel
injection pump to bind and seize which, if not corrected,