Chevrolet 10 Series 1968, Service Manual, Page: 444 / 713

ENG IN E -E LE C TR IC A L 6 Y -1 9
Field Relay Adjustment
1. Point Opening: The point opening is checked as il­
lustrated in Figure 21c. If adjustment is necessary,
carefully bend the armature stop.
2. A ir Gap: Check the air gap with the points just
touching (fig. 22c). The air gap normally need not be
adjusted. If the point opening and closing voltages
are within specifications, the relay will operate
satisfactorily even though the air gap may not be
exactly according to specifications. If adjustment is
necessary, bend the flat contact spring.
IGNITION SYSTEMS
INDEX
Page
General D e s c r ip t io n ............................................................. 6Y-19
Maintenance and A d ju s tm e n ts ............................................. 6Y-19
P e rio d ic Maintenance....................................................... » 6Y-19
B reaker Point S y s t e m ....................................................6Y-19
B reak erless S y s t e m ....................................................... 6Y-19
Ignition Coil C h e c k .......................................................... 6Y-20
Spark P lu g s ....................................................................... 6Y-20
C a b le s ............. . ................................................................ 6Y-20
G o v e r n o r .......................................................................... 6Y-21
Service O p e r a tio n s .................................................................6Y-21
Distributor Contact P o in ts ................................................ 6Y-21
C l e a n i n g .......................................................................... 6Y-21
R e p la c e m e n t....................................................................6Y-21
Setting Dwell A n g l e ....................................................... 6Y-23
Distributor C o n d e n s e r....................................................... 6Y-24
P erform ance D ia g n o s is ................................................ 6Y-24
R e p la c e m e n t....................................................................6Y-24
Distributor
B reaker Point T y p e .......................................................... 6Y-24
Page
R e m o v a l............................................................................. 6Y-24
D isassem b ly.......................................................................6Y-25
Cleaning and I n s p e c t io n ................................................ 6Y-26
A s s e m b l y .......................................................................... 6Y-27
Governor S e t t in g .......................... . . ............................ 6Y-28
Installation.......................................................................... 6Y-28
Magnetic Pulse D is t r ib u t o r ............................................. 6Y-30
R e m o v a l............................................................................. 6Y-30
D isassem bly.......................................................................6Y-30
Installation ....................................................................... 6Y-31
Ignition Pulse A m p l i f i e r .......................................................6Y-31
D isassem bly.......................................................................... 6Y-31
Component C h e c k s ............................................................. 6Y-31
R e a s se m b ly .......................................................................... 6Y-33
Ignition Switch R e p la c e m e n t............. . ................................6Y-33
Spark P lu g s ............................. . ............................................ 6Y-33
Cleaning and R e g a p p in g ............................................. 6Y-33
I n s t a lla t io n .......................................................................... 6Y-34
Truck Engine Overspeed W a rn in g ............................. ... 6Y-34
GENERAL DESCRIPTION
There are two ignition systems available on 1968
vehicles. The breaker point type which is continued as
the regular production system and the optional transistor
controlled breakless ignition system (magnetic pulse
type). The transistor ignition system features a specially
designed distributor, control unit (ignition pulse ampli-
flier), and a special coil. Two resistance wires are also
used in the circuit; one as a ballast between the coil
negative terminal and ground, while the other resistance
wire provides a voltage drop for the engine run circuit
and is by-passed at cranking. The other units in the
system (the ignition switch, spark plugs, and battery)
are of standard design. The distributor and control unit
(ignition pulse amplifier) are shown in Figures li and 2i.
Although the external appearance of the distributor
resembles a standard distributor, the internal construc­
tion is quite different. As shown in the exploded view
(fig. 23i) an iron timer core replaces the conventional
breaker cam. The timer core has the same number of
equally-spaced projections, or vanes as engine cylinders.
The timer core rotates inside a magnetic pick-up
assembly, which replaces the conventional breaker plate,
contact point set, and condenser assembly. The magnetic
pick-up assembly consists of a ceramic permanent mag­
net, a pole piece, and a pick-up coil. The pole piece is
a steel plate having equally spaced internal teeth, one
tooth for each cylinder of the engine.
The magnetic pick-up assembly is mounted on a plate
over the main bearing of the distributor housing. The
timer core is made to rotate about the shaft by
conventional advance weights, thus providing centrifugal
advance.
MAINTENANCE AND ADJUSTMENTS
PERIODIC MAINTENANCE
Breaker Point System
The distributor breaker points and spark plugs are the
only ignition system components that require periodic
service. The remainder of the ignition system requires
only periodic inspection to check operation of the units,
tightness of the electrical connections, and condition of
the wiring. When checking the coil, test with a reputable
tester.
Breaker type distributors are equipped with cam lubri­
cator and should have the wick replaced at the same time
contact point set is replaced. It is not necessary to
lubricate the breaker cam when using a cam lubricator.
Do not attempt to lubricate the wick - Replace when
necessary. When installing a new wick, adjust its position
so the end of the wick just touches the lobe of the breaker
cam.
Distributor shaft lubrication is accomplished by a
reservoir of lube around the mainshaft in the distributor
body or through a hinged cap oiler on governor type units.
Breakerless System
Since there are no moving parts in the ignition pulse
amplifier unit mounted forward of the radiator bulkhead,
and the distributor shaft and bushings have permanent
CHEVROLET TRUCK SERVICE MANUAL