Chevrolet 70 1969 Series, Shop Manual

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ENGINE FUEL SYSTEM 6M-21
1 Camshaft 5 Rocker A r m
2 Cam Follower Assy. 6 Injector Assy.
3 Push Rod
7 Cylinder Head
4 Hold-Down Clamp
tpm z i 8 2
Figure 6—Fuel Injector Installed
into the fuel injector in case the valve is accident­
ally held open by a small particle of dirt. The in­
jector plunger is then returned to its original posi­
tion by the injector follower spring. Figure 4 shows
the various phases of injector operation by the
vertical travel of the injector plunger.
Figure 7— Timing Fuel Injector
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 re­
moves all traces of air which might otherwise ac­
cumulate 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 pass­
age and then back to the fuel tank, is directly ad­
jacent to the inlet opening and contains a filter
element exactly the same as the one on the fuel in­
let side.
Changing the position of the helixes, by rotat­
ing the plunger, retards or advances the closing of
the ports and the beginning and ending of the in­
jection period. At the same time, it increases or
decreases the amount of fuel injected into the cyl­
inder. Figure 3 shows the various plunger positions
from N O - L O A D to F U L L - L O A D . 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 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 in­
jection position to full injection position (full rack
movement), the contour of the upper helix advances
the closing Of the ports and the beginning of in­
jection.
The unit fuel injector is one of the most im ­
portant and precisely built parts of the engine. On
this unit depends the injection of the correct amount
of fuel at exactly the right time into the combustion
chamber. Because the injector operates against
high compression in the combustion chamber, ef­
ficient operation demands that injector assemblies
be 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 oper­
ation of the injectors.
IN JE C T IO N TIM IN G
To properly time the injectors, the injector
follower must be adjusted to a definite height rel­
ative to the injector body.
All injectors can be timed during one full rev­
olution of the crankshaft.
1. Place the engine stop lever in the NO-FUEL
position.
2. Rotate the crankshaft in the direction of
engine rotation until the exhaust valves are fully
depressed on the particular cylinder to be timed.
CHEVROLET SERIES 70 -80 H EAVY DUTY TRUCK SH O P M A N U A L