Chapter 3—ENGINE MAINTENANCE
common rail system and the modified common
rail system.
The fuel injection systems used on Atlas
engines and some older models of Cooper-
Bessemer engines are of the basic type. In this
system one untimed, high-pressure pump supplies
fuel at injection pressure to a main header (com-
mon rail). The fuel flows from the header to the
injector valves and nozzles at each cylinder. The
injector valves are cam-operated and timed.
Metering of the fuel is controlled by the length
of time the nozzle remains open and by the
pressure maintained by the high-pressure pump
in the common rail.
The modified common rail system (constant
pressure), found on newer models of Cooper-
Bessemer engines, uses a high-pressure pump to
maintain fuel at the injection pressure in an
accumulator bottle. The fuel is metered by
individual valves mounted on the side of the
engine; it then flows to the pressure-operated
nozzles in the cylinder head, to be atomized and
distributed in the cylinder.
Since complete details for the maintenance and
repair of each of the various fuel systems in serv-
ice are beyond the scope of this book, specific
information on a particular fuel injection system
must come from the appropriate manufacturer’s
technical manual.
FUEL INJECTION PUMPS
AND INJECTORS
In any discussion of a fuel system, the impor-
tance of each of its parts cannot be overlooked.
The first requirement for trouble-free operation
of a fuel system is clean fuel. Accordingly, the
filters, the strainers, the tanks, the transfer pumps,
and the lines must be maintained according to
prescribed instructions. Even when these parts
function properly, the principal elements of the
injection system—pressure pump, injection
valves, and injection nozzles—are subject to
troubles. The following discussion covers some
of these troubles, their symptoms and causes, and
provides general information concerning
maintenance and repair of this equipment. As you
study this information, keep in mind the dif-
ferences which may exist between the various
systems. (A system, for example, may be of the
jerk pump or common rail type, or the pressure
pump and the injector may be separate or
combined.)
Damaged Plunger
In the plunger and barrel assembly of a high-
pressure pump and in the plunger and bushing
assembly of a unit injector, the symptoms and
causes of damage are similar.
Damage may become apparent through erratic
engine operation. Symptoms vary widely and may
include failure of the engine to develop full power,
low exhaust temperature, low firing pressure for
the affected cylinder, difficulty in balancing
(calibrating) the pumps or injectors, and failure
of one or more cylinders of the engine to fire.
Damage to a plunger and the part in which it slides
may also be recognized by testing the unit on a
test stand. However, the best way to determine
the extent of damage is to disassemble the unit,
clean it thoroughly, and then carefully inspect
each part.
Cleaning of the units can be best accomplished
by use of an approved solvent. Clean diesel fuel
may be used when more effective cleaners are not
available. A brush must be used with diesel fuel
and even then, removal of gummy deposits is dif-
ficult. Keep each plunger and barrel (bushing)
together during the inspection to avoid improper
assembly, as they are manufactured in matched
sets.
The use of a magnifying glass during the
examination of a plunger will facilitate the detec-
tion of damage. Inspect for fine scratches, dull
surface appearance, cracks, pit marks (usually
accompanied by dark discoloration), and erosion
and roughness at the edge of the helix or at the
end of the plunger. An example of a badly scored
plunger is illustrated in A of figure 3-14.
A plunger with the lapped surface and helix edge
in good condition is shown in B of figure 3-14.
Surface irregularities in the region illustrated are
serious because they affect metering and, conse-
quently, engine operation.
When examining a barrel or bushing, search
for erosion of the ports or scoring of the lapped
surfaces. Pay particular attention to the lapped
plane surface at the end of a pump barrel. Rust
or pit marks on this surface must be removed by
lapping before reassembly.
3-17
