Chevrolet 70 1969 Series, Shop Manual

Page: 285 / 913

G ASO LINE ENGINES 6A-14
1 Bearing
2 Housing
3 G ear and Shaft A ssy .
4 Thrust W a sh er
5 Cover and Bushing Assy.
6 Cover Screw and Lock
W a sh er
7 Drive Gear
8 Drive Bolt (In Camshaft)
9 Gasket
10 Bushing (In Housing)
11 G ear Shaft Bushing
Figure 20— Tachometer Drive Components
3. On engines with hydraulic type governor,
position oil line (2, fig. 18) at fittings on cylinder
block and oil pump and start oil line nuts.
4. Install oil pump-to-cylinder block bolts
and tighten to 30 to 35 foot-pounds torque. Tighten
oil line nuts on engine with hydraulic governor.
5. Install engine oil pan, following instructions
previously given in "Engine Oil Pan Replacement."
TACHOMETER DRIVE ADAPTER
REPLACEMENT
R E M O V A L (Fig. 19)
1. Remove floor pan from cab on conventional
cab models, or remove shield from cab rear sup­
port on tilt cab models.
2. Disconnect tachometer drive shaft housing
(1) from adapter (3).
3. Remove two bolts and lock washers (4) at­
taching adapter (3) to cylinder block.
4. Remove adapter assembly and gasket from
cylinder block.
N O T E : If there is insufficient clearance for
adapter removal, try turning engine crankshaft to
position drive bolt (8, fig. 19) in camshaft so drive
slot is in vertical position.
5. Referring to figure 20, remove cover (5)
and inspect teeth on gears (3 and 7). Clean oil holes
in cover.
IN S T A L L A T IO N
1. Lubricate adapter parts with clean engine
oil and attach cover to housing with screws and
lock washers (6, fig. 20).
2. Check drive bolt (8, fig. 20) to make sure it
is firmly tightened into threads in camshaft. If
necessary, turn engine crankshaft to position drive
bolt slot in vertical position.
3. Align tongue on adapter shaft with drive
bolt slot, then place new gasket at cylinder block
and install adapter assembly. Connect flexible
drive shaft housing to adapter.
4. Check tachometer drive cable and housing
routing. There must be no sharp bends or kinks
in the assembly. Lubricate tachometer drive cable
with approved lubricant (Type ST-640) or equiv­
alent.
VALVE TIMING CHECK
When a check of valve timing is necessary,
the following procedure may be used referring to
markings at crankshaft pulley hub or pulley for
determining upper-dead-center on No. 1 cylinder.
1. Remove left-hand rocker cover from cyl­
inder head to provide access to rocker arms at
No. 1 cylinder.
2. Turn engine clockwise (viewed from front
of engine) to U D C #1 mark at crankshaft pulley on
compression stroke. Both the intake and the ex­
haust valve on No. 1 cylinder will then be closed.
3. Set No. 1 exhaust valve lash on 401M and
478M engines at 0.099 inch.
4. Turn engine clockwise until No. 1 exhaust
valve opens and begins to close, then with fingers,
try turning push rod of No. 1 exhaust valve as en­
gine is cranked slowly. When push rod rotates with
finger pressure, the 5 degree (BUDC) mark on
pulley should be at pointer. This will be about 1
revolution from starting point. H push rod starts
to rotate at any point between 10 degree mark and
UD C #1 mark, the valve timing is correct. Be sure
to adjust exhaust valve clearance to 0.018 inch
after performing the foregoing check.
N O T E : A mismatched gear tooth or chain en­
gagement can be recognized by the following error
in timing mark position when following the above
procedure:
401M or
478M E n g i n e ................ ..................................
12°
5. To correct the timing, remove the engine
front cover assembly, then align marks on sprock­
ets or gears.
CHEVROLET SERIES 70-80 HEAVY DUTY TRUCK SH O P M ANUAL