Engine Lubrication - GMC G Service Manual

6A7-2 4.8 LITER L6
4.8L engines are inline six-cylinder (L6) type, overhead
valve, water-cooled engines, with a cast iron block and
head.
The crankshaft is supported by seven precision-insert
main bearings, with crankshaft thrust taken at the number
seven (rear) bearing.
The camshaft is supported by four plain-type bearings
and is gear-driven. Motion from the camshaft is transmitted
to the valves by hydraulic lifters, pushrods, and ball-type
rocker arms. The valve guides are integral with the cylinder
head.
The connecting rods are forged steel, with precision-
insert-type crankpin bearings. The piston pins are a press-
fit in the connecting rods.
The pistons are cast-aluminum alloy. The piston pins are
a floating-fit in the pistons.

ENGINE LUBRICATION

Lubrication schematics are shown in figures 1 and 2.
The gear-type oil pump is driven through an extension shaft
from the distributor drive shaft, which is gear-driven from
the camshaft. Oil is drawn into the oil pump through a
pickup screen and pipe.
Pressurized oil is routed to the oil filter. In case of exces­
sive back-pressure at the oil filter, a bypass valve is pro­
vided. This valve will allow oil flow to the main oil gallery at
the right side of the block. This galiery supplies oil to the
camshaft bearings, hydraulic lifters and main bearings. The
connecting rods are supplied with oil from the main bear­
DESCRIPTION
ings by means of drilled passages in the crankshaft. The
valve train is supplied with oil by the hydraulic lifters. Oil is
pumped from the lifters through the hollow pushrods to the
rocker arms, and drains back to the crankcase through oil
drain holes and the pushrod holes. The piston, piston pin
and timing gears are lubricated by oil splash from the rota­
tion of the crankshaft and connecting rods in the pool of oil
in the oil pan.