Chevrolet 70 Series 1970, Service Manual

Page: 377 / 841

GASOLINE ENGINES 6A-6
1 Crankcase Ventilation 4 Rocker Arm Cover
Valve Assembly 5 Cylinder Heads
2 Carburetor Air Cleaner 6 Ventilation Hose
3 Breather Cap
1 -4 3 2 :
Figure 5 —Schematic Arrangement of Crankcase
Ventilation System Components
CHECKING GENERATOR
AND CHARGING CIRCUIT
R efer to ENGINE ELECTRICAL (SEC. 6Y) in
th is manual for procedure required to check p e r ­
form an ce of charging circu it units and w iring.
COOLING SYSTEM INSPECTION
R efer to ENGINE COOLING SYSTEM (SEC.
6K) in th is manual for arrangem ent of cooling
s y s te m units and for inspection and required
m aintenance p ro ced u res.
CARBURETOR THROTTLE
AND CHOKE LINKAGE
On m ost v e h ic le s it w ill be n e c e ssa r y to r e ­
m ove a ir clean er or a ir intake hose adapter at
carburetor to o b serv e choke operation and action
o f throttle linkage. A ll linkage must be m aintained
in fr e e working condition and should be checked as
p art of tune-up p roced u re. Oil linkage pivot points
if any binding is evident. Com plete inform ation on
th rottle linkage is given in ENGINE FUEL SYSTEM
(SEC. 6M) in this manual.
CARBURETOR IDLE SPEED AND
IDLE MIXTURE ADJUSTMENTS
R efer to ENGINE FUEL SYSTEM (SEC. 6M)
in th is manual for appropriate p roced u res for ad­
justing carburetors.
INSPECTING ELECTRICAL EQUIPMENT AND
ENGINE PERFORMANCE WITH INSTRUMENTS
1. Hook up te st equipment for u se in making
final adjustm ents. Equipment required c o n sists of
dw ell m eter, tachom eter, vacuum gauge andtim ing
light.
2. With engine running at id le speed, check
dwell angle and readjust if n e c e ssa r y .
3. With vacuum lin e to distributor d iscon n ect­
ed and plugged, run engine at id le speed and check
ignition tim ing with tim ing light. L oosen d istrib ­
utor clam p and rotate distributor body to change
tim ing as required. Tighten distributor clamp and
connect vacuum lin e after checking tim ing.
4. While observing vacuum gauge and tach­
o m ete r, s e t engine id le sp eed and adjust carburetor
id le m ixture sc r e w s to provide steady running
engine. ENGINE FUEL SYSTEM (SEC. 6M) in th is
manual c o v ers in stru ction s for adjusting carbur­
etors .
NOTE: If difficulty is experienced in obtaining
sa tisfa cto ry engine id le p erform ance, the cause
may be due to m alfunction of crankcase ventilation
v a lv e s. Inspection and s e r v ic e of ventilation valves
are covered la ter under appropriate headings
under "Crankcase V entilation S y ste m .”
5. R efer to ENGINE ELECTRICAL (SEC. 6Y)
of th is manual for in stru ction s for checking voltage
and current regulator settin g s, generator output,
and sp ecifica tio n s on e le c tr ic a l equipment units.
CRANKCASE VENTILATION SYSTEM
A ll engines have c lo sed , p o sitiv e type crank­
c a se ventilation sy ste m . Fum es and vapors which
would contam inate atm osphere are evacuated from
cran k case and valve com partm ent through ven tila­
tion va lv es which regulate the flow of g a s e s into
intake valve p orts in cylinder heads.
Figure 5 shows, schem atic arrangem ent of
crankcase ventilation units fo r V6 engine.
Ventilation va lv es on V6 engines cannot be
d isa ssem b led but can be rem oved with w rench for
inspection. F igure 6 shows the d esign of v a lv es
for each type of engine.
If, when perform ing tune-up operations, the
engine does not id le sm oothly i t e r a ll checking
and adjusting is done, the crankcase ventilation
v a lv es may be cau se of u n satisfactory perform ance
at id le speed.
INSPECTION AND UNIT REPLACEMENT
1. Rem ove rock er arm cover from each c y l­
inder head.
CHEVROLET SERIES 70-90 HEAVY DUTY TRUCKSHOP MANUAL