Engine Lubrication - Chevrolet 1980 Light Duty Truck Service Manual

6A1-2 IN-LINE 6
V A LV E TRAIN
A very simple ball pivot-type train is used. Motion is
transmitted from the camshaft through the hydraulic lifters
and push rods to the rocker arms. The rocker arm pivots
on its ball and transmits the camshaft motion to the valve.
The rocker arm ball is retained by a self locking nut.
H Y D R A U LIC V A LV E LIF T E R S
Hydraulic Valve Lifters are used to keep all parts of
the valve train in constant contact for quiet operation.
The hydraulic lifter assembly consists of: the lifter
body, which rides in the cylinder block boss, a plunger, a
push rod seat, a metering valve, a plunger spring, a check
ball and spring, a check ball retainer and a push rod seat
retainer.
When the lifter is riding on the low point (base circle)
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 check ball traps the oil in the reservoir below the
plunger. The plunger and lifter body then rise as a unit,
pushing up the push rod and opening the valve. A very small
amount of oil will leak out between the plunger and the
body.
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
Full pressure lubrication, through a full flow oil filter
is furnished by a gear-type oil pump. The distributor, driven
by a helical gear on the camshaft, drives the oil pump.
Oil drawn by the pick-up screen and pipe is pressurized
in the pump and routed to the oil filter. If excessive
backpressure is encountered at the filter, a bypass valve
allows oil flow to the main oil gallery, located along the right
side of the block. This rifle drilled gallery supplies oil to the
camshaft bearings, the hydraulic lifters and the crankshaft
main bearings.
rod. The ball check valve will then move off its seat and the
lifter reservoir will be refilled with oil.
IN TA KE M AN IFO LD
The intake manifold is of cast iron, single level design
for efficient fuel distribution. The 4.1 L (D) manifold is an
integral unit with the head on all vehicles. 4.8 L (T) engines
use separate components. The carburetor pad is centrally
located with an early fuel evaporation (EFE) passage
running underneath the pad, through which exhaust gases
are forced, to promote faster fuel vaporization when the
engine is cold. An exhaust gas recirculation port is also cast
into the manifold on 4.1 L (D ) engines, for the induction
of a metered amount of exhaust gases into the air and fuel
mixture which has entered through the carburetor.
E X H A U S T M AN IFO LD
On 4.8 L (T) engines a single four port, underslung,
center take down manifold of cast ironl is used to direct
exhaust gases from the combustion chambers. On 4.1 L (D )
engines a single four port, underslung, dual center take
down manifold of cast iron is used. A heat shield is mounted
to the manifold that is used to route heated air to the air
cleaner for better fuel vaporization.

Engine Lubrication

The connecting rod bearings are supplied oil from the
crankshaft main bearings by means of cross drilled passages.
The valve train is supplied its lubrication from the valve
lifters. Oil within the lifters is pumped up through the top
of the lifters through the hollow push rods to the rocker
arms. From the head, oil is drained back to the crankcase
through oil drain back holes and the push rod holes. (Fig.
6A1-1).
LIG H T T R U C K S ER V IC E M ANUAL