Pontiac FIREBIRD 1972 Service Manual page 564

6-52 1972 PONTIAC SERVICE MANUAL
RETAINER
RING
-
ROCKER FEED
METERING VALVE-
BALL CHECK
VALVE
BALL CHECK
VALVE RETAINER
PUSH ROD
SEAT
.PLUNGER
.
BALL CHECK
VALVE SPRING
-PLUNGER
SPRING
Fig. 6-87 Valve Lifter
-
High Ball Type
The hydraulic valve lifter functions as follows: When the
lifter is riding od the low point of the cam the plunger
spring keeps the plunger and push rod seat in contact with
the push rod.
When the lifter body begins to ride up the cam lobe, the
ball check valve cuts off the transfer of oil from the reser-
voir below the plunger. The plunger and lifter body then
rise as a unit, pushing up the push rod and opening the
valve.
As the lifter body rides down the other side of the cam,
the plunger follows with it, until the valve closes. The lifter
body continues to follow the cam to its low point, but the
plunger spring keeps the plunger in contact with the push
rod. The ball check valve will then move off its seat and
the lifter reservoir will remain full.
During operation a small amount of oil leaks out of the
lifter between the plunger and body. A controlled amount
of leakage is important to provide continuous adjustment
of the plunger position within the lifter. This leakage is
called "leak-down" and must be within certain limits to
provide correct operation.
Oil is supplied to the lifter by the cylinder block oil gallery
to replace that lost through leak down. The annular
groove around the outside of the lifter body indexes with
the passage drilled from the gallery to the lifter boss. Oil
then enters the lifter from this groove and passes into the
plunger cavity. From the plunger cavity, oil under pres-
sure is also fed up the push rod to lubricate the friction
area between the upper end of the push rod and the rocker
arm.
Fig. 6-88 Two Barrel Carburetor llitake Manifold
-
Typical
The hydraulic valve lifter used in all models incorporates
a restricted orifice plate installed in the plunger counter
bore between the plunger cavity and push rod seat. Its
function is to meter the oil supplied under pressure
through the push rod to the drilled rockers in the engine,
using the push rod and drilled rockers for lubricating the
upper valve train.
FUEL DISTRIBUTION SYSTEM
The intake manifold is designed to provide fuel passages
which are short and practically equal in length. With the
two-barrel carburetor, each throat of the carburetor feeds
four cylinders as shown in Fig. 6-88. The intake manifold
used with the four-barrel carburetor is fundamentally the
same as with the two-barrel type, but has four openings to
index with the carburetor throats. With the four-barrel
carburetor the two throats on the right side feed four
cylinders and the two throats on the left side feed four
cylinders.
A stove is included in the intake manifold surrounding the
risers which lead to the carburetor. When the engine is
cold, exhaust gases from both banks of cylinders pass
through a passage in the intake manifold to circulate
around and heat the stove. The fuel-air mixture passing
from the carburetor to the cylinders is thereby pre-heated
to the desired temperature for proper combusiion.
I
COOLAN
r
CIRCULATION
PASSAGE
EXHAUST
CROSSOVER
PASSAGE
INTAKE PORTS
Fig. 6-89 Intake Manifold
-
Side View