GMC 4000 Series Service Manual page 418

IF ENGINE HAS NOT BEEN CRANKED
(V-6 ENGINE MODELS)
1. If distributor is new, No. 1 firing position
can be determined by the mark made on the old
distributor housing prior to removal. Also locate
mark made on housing after gears were disengaged.
2. Place new distributor to cylinder block gas­
ket on block, and lubricate distributor drive gear.
3. Turn rotor so segment points to the mark
made after disengaging gears. As distributor is
inserted into place, spiral gear will cause rotor
to turn counterclockwise. It may be necessary to
insert the assembly several times to find the cor­
rect position to bring rotor segment to No. 1 firing
position.
4. Tighten distributor clamp bolt snugly and
connect vacuum line(s). Connect primary wire to
coil terminal and install cap. Install sparkplugs
and high tension w ires, if removed.
5. Check ignition timing as explained previ­
ously under "Ignition Timing."
IF ENGINE HAS BEEN CRANKED
(IN-LINE ENGINES)
1. Locate No. 1 piston in firing position by
either of two methods described below:
a. Remove No. 1 spark plug and, with finger
on plug hole, crank engine until compression is
felt in No. 1 cylinder. Continue cranking until tim ­
ing mark on crankshaft pulley is aligned with 4°
BUDC mark on timing tab.
b. Remove rocker arm cover and crank engine
until No. 1 intake valve closes. Continue to crank
slowly about 1/3 turn until timing mark on pulley
lines up with the 4° BUDC mark on timing tab.
2. Place a new gasket on block; then position
distributor to opening in block in normal installed
attitude, noting position of vacuum control unit.
3. Position rotor to point toward front of en­
gine (with distributor held in installed attitude),
then turn rotor counterclockwise approximately
1/8 turn and push distributor down to engine cam­
shaft. It may be necessary to rotate rotor slightly
until engagement is felt.
4. While pressing down on distributor, engage
starter several tim es to make sure oil pump shaft
is engaged. Install distributor hold-down clamp
and bolt and snug up bolt.
5. Turn distributor body slightly until points
just begin to open and tighten clamp bolt.
6. Place distributor cap in position and check
to see that rotor lines up with terminal for No. 1
spark plug.
7. Install distributor cap. Install spark plug
w ires in cap in correct firing sequence - - 1-5-3-
6-2-4 - - starting with No. 1 wire in socket adjacent
to No. 1 firing position mark on distributor hous­
ing, then proceeding clockwise around the cap. In­
stall Hi-tension wire from ignition coil in center
G M C S E R V I C E M A N U A L
socket in distributor cap. Connect distributor prim­
ary wire to negative (-) terminal on ignition coil.
unit on distributor.
under "Ignition Timing" previously.
IF ENGINE HAS BEEN CRANKED
(V-6 ENGINES)
Turn engine over by intermittently operating start­
er and observe movement of No. 1 intake valve
(second valve from front). When intake valve starts
to close (move up), continue to turn engine slowly
until pointer on timing gear cover is at proper
timing mark on crankshaft pulley (fig. 3). Engine
is then in No. 1 firing position.
previously. It may be necessary to turn the oil
pump drive shaft to permit engagement of drive
shaft with distributor drive gear.
screw .
wires in cap in correct firing sequence — 1-6-5-
4_3_2 - - starting with No. 1 wire in socket ad­
jacent to No. 1 firing position mark on distributor
housing, then proceeding clockwise around the cap.
Install secondary wire from ignition coil in center
socket in distributor cap. Connect distributor prim ­
ary wire to negative (-) terminal on ignition coil.
ously directed under "Ignition Timing."
nected across the points, reduces point arc by its
ability to store up electrical energy.
REMOVAL AND INSTALLATION
remove cap, and place it out of the work area.
tact point quick-disconnect terminal.
condenser from breaker plate, and wipe breaker
plate clean.
cedure outlined above.
TEST
each must be considered in making tests.
ing material, causing direct short between metallic
elements of condenser. This condition prevents
any condenser action.
IGNITION SYSTEM
8. Connect vacuum line(s) to vacuum advance
9. Start engine and adjust timing as explained
1. Remove left-hand valve rocker arm cover.
2. Install distributor as described in Step 1
3. Install distributor hold-down clamp and cap
4. Install distributor cap. Install spark plug
5. Check and adjust ignition timing as previ­
DISTRIBUTOR CONDENSER
Condenser, mounted on breaker plate and con­
1. R elease distributor cap hold-down screw s,
2. Remove rotor.
3. Disconnect condenser lead wire from con­
4. Remove condenser attaching screw, lift
5. Install new condenser, using reverse of pro­
Four factors affect condenser operation, and
Breakdown. Breakdown is a failure of insulat­
Sec. 6Y
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