Pontiac FIREBIRD 1972 Service Manual page 526

1972 PONTIAC SERVICE MANUAL
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1
Fig. 6 - 1 3 Intake and Exhaust Manifolds
FUEL DISTRIBUTION SYSTEM
A single-barrel Monojet carburetor with an automatic
choke provides fuel to the intake manifold.
The intake manifold is positioned directly above the ex-
haust manifold (Fig. 6-1
3).
This design allows hot exhaust
to heat the cool, incoming fuel mixture.
The side-by-side location of the intake and exhaust valves
along with joined parts permit the use of a three-port
intake manifold and four-port exhaust manifold (Fig. 6-
13).
EXHAUST SYSTEM
The four-port, cast iron exhaust manifold contains a heat
riser valve. This thermostetically controlled valve is
located below the exhaust manifold in front of the exhaust
pipe inlet. When the engine is cold, the valve closes, direct-
ing the exhaust upward in the exhaust manifold and caus-
ing the hot exhaust to warm the stove beneath the
carburetor. The fuel mixture is warmed by passing above
Fig. 6-14 Combustion Chamber
the stove. The heat riser valve opens as the engine warms
UP.
COMBUSTION CHAMBERS
Combustion chambers are cast to insure uniform shape for
all cylinders. Spark plugs are located near intake valves for
maximum power and to properly fire economically lean
mixtures.
The contoured wedge shape of the combustion chamber
(Fig. 6-14) minimizes the possibility of detonation, facili-
tates breathing and provides swirling turbulence for
smooth, complete combustion.
Intake valves are large and have 46" seat angles to further
provide easy breathing for high combustion efficiency.
Exhaust valve seat angle is also 46".
GENERAL INFORMATION ON ENGINE SERVICE
The following information on engine service should be noted easiest way to keep the lifters clean. Second, lifters should
carefully, as it is important in preventing damage and in always be replaced in the same bosses from which they
contributing to reliable engine performance. were removed.
Cleanliness is a primary factor when servicing the engine.
The slightest particle of dirt that finds its way into a
hydraulic lifter may cause a malfunction.
Since any dirt which may enter the oil galleries or passages
in the engine could eventually get to a lifter, cleanliness
should be exercised when any part of the engine is
removed or disassembled.
When lifters are removed for any reason, they should
immediately be placed in order in a valve lifter storage
box. This is important for two reasons. First, it is the
Valves, valve lifters, push rods, rocker arms, rocker arm
balls and nuts should always be kept in sets and returned
to their original positions. These parts will tend to mate
as the engine operates and will provide more satisfactory
operation when kept together. By storing lifters in a stor-
age box and valves, push rods, rocker arms, balls and nuts
in a holding stand (Fig. 6- 15) whenever they are removed,
they can easily be kept in sets for identification during
assembly. In addition to keeping the parts in sets, the push
rods should be replaced with the same end up. In other
words, the same end will contact the rocker arm as before
the engine was disassembled. The upper end can usually