DETROIT DIESEL 53
Fig. 8 Checking Rack and Plunger for Free Movement
injector in case the valve is accidentally held open by a small particle of dirt. The injector plunger is then returned to its
original position by the injector follower spring. Figure 4 shows the various phases of injector operation by the vertical
travel of the injector plunger.
On the return upward movement of the plunger, the high pressure cylinder within the bushing is again filled with fuel oil
through the ports. The constant circulation of fresh cool fuel through the injector renews the fuel supply in the chamber,
helps cool the injector and also effectively removes all traces of air 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 directly adjacent to the inlet opening.
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 position (full rack _movement), the contour of_ the, upper helix advances the closing of the ports and the
beginning of injection.
General Instructions for Injector Care and Overhaul
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 exactly the right time depends upon this unit. Because the injector operates
against high compression pressure in the combustion chamber, efficient operation 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
type fuel filters and clean water-free fuel are the keys to trouble-free operation of the injectors.
Due to the close tolerances of various injector parts, extreme cleanliness and strict adherence to service instructions is
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 fan which draws air into the room through a filter. This pressure prevents particles of
dirt and dust from entering the room through the doors and windows. A suitable air outlet will remove solvent fumes
along with the outgoing air. Also provide a source for 110 volt alternating current electric power.
Fig. 9 Injector High Pressure Test