General Description; Engine Construction; Cylinder Block; Cylinder Heads - GMC T Series 1994 Repair Manual

ENGINE CONSTRUCTION

The 4.3L engine, RPO LB4 (VIN Z), is a liquid-cooled
90-degree V6 type with overhead valves, cast iron
block, and cylinder heads. 4.3L (VIN Z) engines used in
C/K/S/T vehicles have a cast-iron balance shaft mount­
ed in the crankcase above and inline with the camshaft.
For engine identification, refer to SECTION OA. For
engine com ponent identification refer to figures 1
through 6.

CYLINDER BLOCK

The cylinder block has 6 cylinders arranged in a "V"
shape with 3 cylinders in each bank. Starting at the
front of the engine, cylinders in the right bank are num­
bered 1-3-5 and cylinders in the left bank are numbered
2-4-6 (when viewed from the front of the engine). The
firing order of the cylinders is 1-6-5-4-3-2. The cylinders
are encircled by coolant jackets.

CYLINDER HEADS

The cylinder heads have one intake and one exhaust
valve for each cylinder. A spark plug is located between
the valves in the side of the cylinder head. The valve
guides are integral and the rocker arms are retained on
individual threaded-in or pressed-in studs (depending
on where the engine was built).
CRANKSHAFT
The crankshaft is supported by four main bearing
inserts. The number four bearing at the rear of the
engine is the end thrust bearing. The bearings are
retained by bearing caps that are machined with the
block for proper alignment and clearances.
CAMSHAFT
The camshaft is supported by four full round, sleeve
type bearings. A sprocket on the crankshaft drives a
timing chain which in turn drives the camshaft through a
sprocket.

PISTONS AND CONNECTING RODS

The pistons are made of cast aluminum alloy using
two compression rings and one oil control ring. Piston
pins are offset 1.6 mm (1/16 inch) toward the major
thrust side (right-hand side) to reduce piston slap as the
connecting rod travels from one side of the piston to the
other side after a stroke. The pins are a press fit in the
connecting rod and a floating fit in the piston.

GENERAL DESCRIPTION

BALANCE SHAFT

S/T Vehicles and C/K Vehicles with light duty
emissions
The cast-iron balance shaft is mounted in the crank­
case above and in line with the camshaft. A camshaft
gear drives the gear attached to the balance shaft. The
front end of the balance shaft is supported by a ball
bearing and the opposite end uses a sleeve bearing.

VALVE TRAIN

The valve train is a ball pivot type. Motion is transmit­
ted from the camshaft through the hydraulic lifter and
pushrod to the rocker arm. The rocker arm pivots on its
ball and transmits the camshaft motion to the valve.
The hydraulic valve lifters with roller followers keep all
parts of the valve train in constant contact. Each lifter
acts as an automatic adjuster and maintains zero lash
in the valve train and eliminates the need for periodic
valve adjustment.

INTAKE MANIFOLD

A cast-iron intake manifold is used that has an
exhaust gas recirculation (EGR) port cast into it for the
mixture of exhaust gases with the fuel and air mixture.

ENGINE LUBRICATION

Lubrication schematics are shown in figures 7 through
10. 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
excessive oil pressure, a bypass valve is provided. Fil­
tered oil flows into the main gallery and then to the
camshaft, balance shaft rear bearing (S/T vehicles), 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 overhead drains back to the crankcase through oil
drain holes.
The timing chain is drip fed from the front camshaft
bearing. The pistons and piston pins are lubricated by
oil splash.