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6A3-2
1977 PONTIAC SERVICE MANUAL
removed.
The intake manifold utilizes a low restriction, dual
intake manifold. It is bolted to the inner edges of both
cylinder heads so that it connects with all inlet ports. Since
the intake manifold is cast iron, as is the carburetor throttle
body, the manifold incorporates a special exhaust heat
passage to warm the throttle body.
The E.G.R. System, used has a cast passage from the
exhaust heat passage to the E.G.R. valve and from the valve
to a hole in the floor of the intake manifold under the
carburetor.
Each exhaust and intake valve has a spring of
ample capacity to insure positive seating throughout the
operating speed range.
The valve rocker arms for each bank of cylinders are
mounted on a tubular steel shaft supported on the cylinder
head by three pedestals. The rocker arms are stamped steel.
Hydraulic valve lifters and tubular push rods are
used to operate overhead rocker arms and valves of both
banks of cylinders from a single camshaft. This system
requires no lash adjustment at time of assembly or in service.
Construction and operation of hydraulic valve lifters are
described below.
In addition to its normal function of a cam follower, each
hydraulic valve lifter also serves as an automatic adjuster
which maintains zero lash in the valve train under all
operating conditions. By eliminating all lash in the valve train
and also providing a cushion of oil to absorb operating
shocks, the hydraulic valve lifter promotes quiet valve
operation. It also eliminates the need for periodic valve
adjustment to compensate for wear of parts.
As shown in Fig. 6A3-2 all parts of a hydraulic lifter are
housed in the lifter body, which is the cam follower.
LIFTER BODY
PUSH ROD SEAT
METERING VALVE
CHECK BALL
CHECK BALL
RETAINER
PUSH ROD SEAT
RETAINER
PLUNGER
CHECK BALL SPRING
1
1
9. PLUNGER SPRING
4801
Fig. 6A3-2 Hydraulic Valve Lifter
Oil is fed to all lifters through galleries in the crankcase.
Oil enters each lifter through grooves and oil holes in the lifter
body and plunger, flows down into the chamber below the
plunger through the feed hole and around the check ball. The
first few cycles of operation after the engine is started forces
out all air and completely fills the plunger and lower chamber
of each lifter with oil.
LUBRICATION SYSTEM
The engine lubrication system is of the force-feed type
in which oil is supplied under full pressure to crankshaft,
connecting rods, and camshaft bearings, and is supplied
under controlled volume to the rocker arms, and push rods.
All other moving parts are lubricated by gravity flow or
splash. See Fig. 6A3-3.
Fig. 6A3-3 Schematic Diagram of Engine Oil Flow
The supply of oil is carried in the lower crankcase (oil
pan) which is filled through a filler opening in the left rocker
arm cover. A removable oil gage rod on the left side of the
crankcase is provided to check oil level.
The oil pump is located in the timing chain cover where
it is connected by a drilled passage in the cylinder crankcase
to an oil screen housing and pipe assembly. The screen is
submerged in the oil supply and has ample area for all
operating c~nditions. If the screen should become clogged for
any reason, oil may be drawn into the system through the
relief valve in the screen.
Oil is drawn into the pump through the screen and
pipe assembly and a drilled passage in the crankcase which
connects to drilled passages in the timing chain cover. All oil
is discharged from the pump to the oil pump cover assembly.
The cover assembly consists of an oil pressure relief valve,
an oil filter by-pass valve and a nipple for installation of an
oil filter. The spring loaded oil pressure relief valve limits the
oil pressure. The oil filter by-pass valve opens when the filter
has become clogged, to the extent that approximately 10- 15
pounds pressure difference exists between the filter inlet and
discharge, to by-pass the oil filter and channel unfiltered oil
directly to the main oil galleries of the engine.
An AC full flow oil filter is externally mounted to
the oil filter cover nipple on the lower right front side of the
engine. Normally, all engine oil passes through the filter
element, however, if the element becomes restricted, a spring
loaded by-pass valve opens as mentioned above.
The main oil galleries run the full length of the
crankcase and cut into the valve lifter guide holes to supply
oil at full pressure to the lifters. Holes drilled from the
crankshaft bearings to the main gallery intersect the cam
bearing bores to supply oil to the cam bearings.
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