Gasoline Engines - Chevrolet HM80 Series Service Manual

S ec. 6A-54

GASOLINE ENGINES

AIR HOSE
BUSHING
(As req'd)
3 / 8 " PIPE
THREAD
SPARK PLUG BODY
Figure 2 —A ir Supply A dap ter Tool
and at every 12-m onth or 12,000 m ile interval
th ereafter. A te ste r (AC Type CT-3) is available
for u se in checking the condition of the crankcase
ventilation sy stem . Follow the instructions furn­
ish ed with the te ste r when making sy stem check.
The C T-3 T ester functions a s a p r e ssu r e and
or vacuum gauge. Changes in either the p ressu re
or vacuum w ill m ove a colored viewing drum up­
ward or downward in relation to fixed window open­
in gs. A se le c to r knob on the bottom of te ste r , with
settin g s "A" through "O" perm its te ster calibration
to match air flow through v a lv es. With the CT-3
properly connected to an idling engine, a sin gle
color or a combination of colors of red, green or
orange v isib le in the window openings, indicates
the operating condition of the P o sitiv e Crankcase
Ventilation System . Window reading interpretations,
probable troubles, and rem ed ies are fully covered
in the PCV D iagn osis Chart (fig. 1).
B rief instructions for using the C T -3 tester
are as follow s:
1. Install the dipstick tube plug provided in
the te ste r kit.
2. Set parking brake, sta rt engine, and allow
to id le.
3. Rem ove the breather connection from the
air clean er and p lace the PCV te ste r connection
at the opening to the crankcase (rocker arm cover).
The PCV te ste r should be set to the "M" position
for V6 engine, or to "K" position on V8 engines.
4. A green reading indicates the sy ste m is
operating sa tisfa cto rily and no further testin g is
required. An orange or red reading indicates in­
su fficien t a ir flow in the ventilation lin e. Addition­
al testin g is required to determ ine the cau se.
5. Rem ove rocker arm co v ers and inspect
the crankcase ventilation valves which are screw ed
into threaded ports in cylinder heads.
REMOVE INSULATOR
T -8132
NOTE: One valve is used in each cylinder
head on V6 engines, and two valv es are used in
each cylinder head on V8 engines.
U se socket wrench to rem ove crankcase vent­
ilation valv es in c a se the testin g in dicates a m al­
function in crankcase ventilation sy stem .
Clean valves, h o se s, and breather a ssem b ly,
then in stall p arts and repeat the te st a s previously
d escribed.
If, after ventilation v a lv es an d /or h o ses and
other sy stem components a re in stalled , the test
in dicates unsatisfactory p erform ance of the vent­
ilation sy stem , a check should be made to s e e that
crankcase openings w ere a ll com pletely sealed
during test.
It may be n ec e ssa r y to make rep a irs to engine
components such a s valves, piston rin gs, or oil
s e a ls to make p o ssib le a satisfa cto ry operating
crankcase ventilation sy stem .
VALVE SPRING REPLACEMENT
(V6 AND V8 CYLINDER HEAD)
In m ost v eh icles it is p o ssib le to replace a
broken or defective valve spring without rem oving
cylinder head from engine. Figure 2 show s how to
make an air hose adapter from a discarded spark
plug to be used to connect air lin e to cylinder at
which the valve spring is to be replaced. Adapter
is made from spark plug by cutting off electrod e
and the upper portion of plug body a s shown. R e­
move insulator from body, then thread the body
upper cavity with 3 /8 -in c h pipe tap. Install bush­
ing and fittings as n e ce ssa r y to connect a ir hose.
U se sam e procedure a s d escribed in Service
Manuals ST135-70 and ST332-71 to rep lace valve
sp rin gs and /or valve stem o il s e a ls .
CRANKSHAFT PULLEY AND
HUB REPLACEMENT
NOTE: 401M engines do not u se a crankshaft
damper.
CRANKSHAFT PULLEY
AND/OR HUB REMOVAL
1. Remove radiator if n e ce ssa r y , to provide
a c c e s s to crankshaft p ulley. On engines with fan
blades in sta lled on crankshaft pulley, rem ove fan
blades from crankshaft pulley hub. A lso rem ove
a c c e sso r y drive b elts.
CHEVROLET SERIES 70-90 HEAVY DUTY TRUCK SHOP MANUAL SUPPLEMENT