Whenever a General Motors 53 or 71 series diesel
engine injector has been removed and reinstalled, or a
new injector has been installed, the injector must be
timed and the injector control rack positioned.
To properly time an injector, adjust the injector
follower to a definite height in relation to the injector
body (fig. 4-51). This will vary according to the size of
the injector being used. Check the manufacturer's
manual to determine the proper gauge to use.
Place the engine speed control lever to the shutoff
position and rotate the crankshaft in the direction of
engine rotation until the exhaust valves are fully
depressed on the particular cylinder to be timed. Place
Figure 4-53.--Checking rotating movement of injector control
the small end of the injector timing gauge in the hole
provided in the top of the injector body. Loosen the
control lever to the full fuel position, and hold it in that
pushrod locknut, turn the pushrod, and adjust the
position with light finger pressure. Turn the inner
injector rocker arm until the extended part or shoulder
adjusting screw on the rear injector rack control lever
of the gauge will just pass over the top of the injector
down until a slight movement of the control lever is
follower. Hold the pushrod and tighten the locknut.
observed. This will place the rear injector rack in the
Check adjustment after tightening the locknut and
full fuel position. Turn down the outer adjusting screw
readjust as necessary. By following the sequence of the
until it bottoms lightly on the control tube. Then,
engine firing order, you can time the injectors in one
alternate tightening of the inner and outer adjusting
revolution of the crankshaft.
screws. Torque both to 24 to 36 inch-pounds.
To check the proper adjustment, hold the speed
control in the full fuel position and press down on the
injector rack with a screwdriver. Note the rotating
racks so that all injectors in an engine inject the same
movement of the rack (fig. 4-53). Holding the rack in
amount of fuel at any given engine speed. This is done
the same full fuel position, push downward on the
by adjusting the inner and outer adjusting screw on the
injector control rack with the screwdriver (fig. 4-54).
rack control lever (fig. 4-52). This is a rather delicate
The rack should tilt downward and then spring back
adjustment to make. To equalize the injectors on the
common 53 or 71 series GM diesels used in today's
QEC kits, all inner and outer injector rack control lever
adjusting screws must be loosened. Move the speed
Figure 4-52.--Positioning rear injector rack control lever.
Figure 4-54.--Checking injector rack "spring" action.