DETROIT DIESEL 53
upper helix advances the closing of the ports and the
beginning of Injection.
General Instructions for Injector Care and
The fuel injector is one of the most important and
precisely built parts of the engine The injection of the
correct amount of fuel into the combustion chamber at
exactIy the right time depends upon this unit Because
the injector operates against high compression
pressure in the combustion chamber. effecient opera-
tion demands that the injector assembly is maintained
in first-class condition at all times. Proper maintenance
of the fuel system and the use of the recommended
Fig. 8 Checking Rack and Plunger for Free
type fuel filters and cleatn water-free fuel are the keys
to trouble-free operation of the injectors.
injector in case the valve is accidentally held open by a
Due to the close tolerances of various injector parts.
small particle of dirt The injector plunger is then
extreme cleanliness and strict adherence to service
returned to its original position by the injector
instructtons is required.
follower spring. Figure 4 shows the various phases of
injector operation by the vertical travel of the injector
Perform all injector repairs in a clean. well lighted
room with a dust free atmosphere. An ideal injector
room is slightly pressurized by means of an electric
On the return upward movement of the plunger. the
fan which draws air into the room through a filter.
high pressure cylinder within the bushing is again
This pressure prevents particles of` dirt and dust from
entering the room through the door\ and windows. A
filled with fuel oil through the ports. The constant
circulation of fresh cool fuel through the injector
suitable air outlet will remove solvent fumes along
renews the fuel supply in the chamber. helps cool the
with the outgoing air. Also provide a source for 110
injector and also effective removes all traces of air
volt alternating current electric power
which might otherwise accumulate in the system and
Interfere with accurate metering of the fuel.
The fuel injector outlet opening. through which the
excess fuel oil returns to the fuel return manifold and
then back to the fuel tank is directIy adjacent to the
Changing the position of the helices by rotating the
plunger. retards or advances the closing of the ports
and the beginning and ending of the injection period.
At the same time. it increases or decreases the amount
of fuel injected into the cylinder. Figure 3 shows the
various plunger positions - from no-load to full-load.
With the control rack pulled out all the way (no
injection). the upper port is not closed by the helix
until after the lower port is uncovered. Consequently.
with the rack in this position. all of the fuel is forced
back into the supply chamber and no injection of fuel
takes place. With the control rack pushed all the way
in (full injection). the upper port is closed shortly after
the lower port has been covered. thus producing a
maximum effective stroke and maximum injection.
From this no injection position to full injection
Fig. 9 Injector High Pressure Test
position (full rack movement). the contour of the