Description; Engine Lubrication - GMC G Service Manual

6A3-2 4.3 LITER V6
4.3L engines are 90-degree V6 type, overhead valve,
water cooled engines with a cast-iron block and cylinder
heads.
The crankshaft is supported by four precision-insert
main bearings, with crankshaft thrust taken at the number
four (rear) bearing.
The camshaft is supported by four plain-type bearings
and is chain-driven. Motion from the camshaft is transmit­
ted to the valves by hydraulic lifters, pushrods and ball-type
rocker arms. The valve guides are integral in 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 piston.

DESCRIPTION

Lubrication schematics are shown in figures 1 and 2.
The gear-type oil pump is driven from the distributor 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 oil pressure, a bypass valve is provided. Filtered oil
flows into the main gallery and then to the camshaft and
crankshaft bearings. The valve lifter oil gallery supplies oil
to the valve lifters. Oil flows from the hydraulic lifters
through the hollow pushrods to the rocker arms. Oil from
the overhead drains back to the crankcase through oil drain
holes.
The timing chain is drip-fed from the front camshaft bear­
ing. The pistons and piston pins are lubricated by oil splash.

ENGINE LUBRICATION