When fuel pressure drops below injection
pressure, the return spring closes the fuel valve.
For information on the removal and repair
of the fuel injector nozzle, consult the
manufacturers service manual.
DISTRIBUTOR-TYPE FUEL SYSTEMS
The distributor-type fuel system is found on small-
to medium-sized diesel engines. Its operation is similar
to an ignition distributor found on gasoline engine. A
rotating member, called a rotor, within the pump
distributes fuel at high pressure to the individual
injectors in engine firing-order sequence.
There are several manufacturers of distributor-type
fuel injection systems. Operation of the fuel
distribution is similar, in that a central rotating member
forms the pumping and the distributing rotor is driven
from the main drive shaft on which the governor is
The distributor-type fuel system that will be
discussed is the DB2 Roosa Master diesel fuel-injection
pump, manufactured by Stanadyne's Hartford Division.
The Roosa Master fuel injection pump is described
as an opposed plunger, inlet metering, distributor-type
pump. Simplicity, the prime advantage of this design,
contributes to greater ease of service, low maintenance
cost, and greater dependability. Before describing the
injection pump components and operation, lets
familiarize ourselves with the model numbering
system. For example, model number DB2833JN3000
breaks down like this:
8Number of cylinders
33Abbreviation of plunger diameter; 33, 0.330
JNAccessory code that relates to special pump
Figure 5-12.Drive shaft.
For information on the accessory code and
the specification number for a particular pump,
always refer to the manufacturers service
The main components of the DB2 fuel injection
pump are the drive shaft, distributor rotor, transfer
pump, pumping plungers, internal cam ring, hydraulic
head, end plate, governor, and housing assembly with
an integral advance mechanism. The rotating members
that revolve on a common axis include the drive shaft,
distributor rotor, and transfer pump.
DRIVE SHAFT (fig. 5-12)The drive shaft is the
driving member that rotates inside a pilot tube pressed
into the housing. The rear of the shaft engages the front
of the distributor rotor and turns the rotor shaft. Two lip
type seals prevent the entrance of engine oil into the
pump and retain fuel used for pump lubrication.
DISTRIBUTOR ROTOR (fig. 5-13)The
distributor rotor is the drive end of the rotor, containing
Figure 5-13.Distributor rotor.