Chevrolet 70 Series 1970, Service Manual

Page: 399 / 841

53 AND 71 SERIES DIESEL ENGINES 6C-2
IMPORTANT: F uel sy ste m m ust be prim ed
when engine has run out of fu el.
If ga so lin e is inadvertently poured in the fuel
tank and the engine is operated, the entire sy ste m
m ust be drained, otherw ise the life of fuel sy ste m
com ponents may be ad v ersely affected.
THE FUEL FOR GMC TRUCK DIESEL ENGINE
MUST BE OF GOOD QUALITY. GRADE 2 AND
SHOULD BE OBTAINED FROM ARELIABLE SUP­
PLIER. USE CARE IN STORAGE AND IN HANDL­
ING DIESEL FUEL TO PREVENT CONTAMIN­
ATION BY DIRT AND WATER. DO NOT SMOKE
WHEN HANDLING FUEL.
NOTE: In c a se of com plaints of hard starting
in cold w eather, refer to su ggested r e m ed ies in
"Troubleshooting" under "Hard Starting" la ter in
th is sectio n .
CRANKCASE OIL LEVEL AND
VISCOSITY CHECK
An o il le v e l dipstick at left sid e of engine is
provided for checking crankcase o il le v e l. D ipstick
is marked "L" and "F."
When checking engine o il le v e l, make note of
o il v is c o s ity . If there is evidence of cran k case oil
dilution a s indicated by o il appearing too "thin" or
by le v e l above the "F." mark on dipstick, make
n e c e ssa r y investigation to determ ine cau se of di­
lution and make n e c e ssa r y co rrectio n s.
ENGINE OIL FILTER ELEMENT
O il filte r elem ent changing p eriod s are related
to crankcase o il changing p erio d s, the quality of o il
u sed and se v e r ity of s e r v ic e . R efer to LUBRICA­
TION (SEC. 0) for elem ent replacem ent, o il change
p erio d s, o il sp ecifica tio n s, and v isc o sity .
COOLING SYSTEM INSPECTION
R efer to ENGINE COOLING SYSTEM (SEC. 6K)
fo r arrangem ent of cooling sy ste m units and for
inspection and required m aintenance p roced u res.
CYLINDER HEAD BOLTS
N orm ally the cylinder head bolts should not
require retightening at tune-up in te r v a ls. When
n e c e ssa r y to tighten cylinder head b o lts, refe r to
"Cylinder Head Replacem ent" covered la te r in this
se ctio n , for bolt tightening sequence.
BATTERY AND BATTERY CABLES
If battery is weak or show s other evidence of
being defective, refer to appropriate coverage in
ENGINE ELECTRICAL (SEC. 6Y) of th is manual,
for method of diagnosing battery d e fic ie n c ie s.
CHARGING CIRCUIT WIRING AND
GENERATOR INSPECTION
R efer to ENGINE ELECTRICAL (SEC. 6Y) in
th is manual for procedure required to check p e r ­
form ance of charging circu it units.
CHECKING DRIVE BELTS
1. Inspect drive b elts for e x c e s s iv e w ear and
dam age. If no d efects a re found, check b elts for
proper tension.
2. When installing new drive b elts or adjust­
ing old b e lts, u se tension gauge to provide co rrect
ten sion .
IMPORTANT: Adjusting drive b elts too tightly
w ill im pose too great a load on b earings in the
driven units. Slipping w ill occur if drive b elts a re
not adjusted tight enough. B elt life w ill be shorten­
ed if b e lts a re not properly tightened.
R efer to ENGINE COO LING SYSTEM (SEC. 6K)
for fan b e lts, to AIR COMPRESSOR AND GOV­
ERNOR (SEC. 6T) for a ir co m p resso r b e lts, to
ENGINE ELECTRICAL (SEC. 6Y) for generator
b e lts, and STEERING SYSTEM (SEC. 9B )forp ow er
ste erin g b elts in th is manual for adjustm ent p ro ­
cedure of drive b e lts.
MANIFOLD BOLTS
Exhaust m anifolds a re secu red by lo ck s and
nuts. At tune-up in terval, check a ll exhaust mani­
fold nuts fo r proper torque.
ENGINE TUNE-UP OPERATIONS
PRELIMINARY OPERATIONS
P erfo rm the p relim in ary p roced u res a s d e s­
cribed following:
B efo re tune-up adjustm ents are started , it is
important that a ir cle a n e rs and fuel filte r are
se r v ic e d . C rankcase breather tube and a ir box
drains m ust be kept clean and unobstructed. A ir
box drains may be cleaned with co m p ressed a ir.
IMPORTANT: R em ove or lo o sen an a ir box
hand hole cover, oth erw ise blower or end plate
ga sk ets may be damaged by e x c e s s iv e air p r e ssu r e .
R eferen ce should be made to "Diagnosis and
Troubleshooting" la ter in th is sectio n .
To com pletely tune up an engine, a ll m ajor
adjustm ents m ust be made by follow ing the applic­
able tune-up sequence, after the engine has reach ­
ed its norm al operating tem perature.
CHEVROLET SERIES 70-90 HEAVY DUTY TRUCK SHOP MANUAL