Chevrolet Silverado / GMC Sierra. Manual — part 1889

bearing caps. The engine block is cast iron. The 5 crankshaft bearing caps each have 4 vertical
M10 and 2 horizontal M8 mounting bolts. The camshaft is supported by 5 camshaft bearings
pressed into the block.

Exhaust Manifolds

The exhaust manifolds are a 1-piece cast iron design. The exhaust manifolds direct exhaust gasses
from the combustion chambers to the exhaust system. Each manifold also has an externally
mounted heat shield that is retained by bolts.

Intake Manifold

The intake manifold is a 1-piece composite design that incorporates brass threaded inserts for
mounting the fuel rail, throttle body, and wire harness studs. Each side of the intake manifold is
sealed to the cylinder head by a non-reusable silicone sealing gasket/nylon carrier assembly. The
electronically actuated throttle body bolts to the front of the intake manifold. The throttle body is
sealed by a 1-piece push in place silicone gasket. The fuel rail assembly, with 8 separate fuel
injectors, is retained to the intake by 4 bolts. The injectors are seated into their individual
manifold bores with O-ring seals to provide sealing. A fuel rail stop bracket is retained to the rear
of the left cylinder head by a mounting bolt. The manifold absolute pressure (MAP) sensor is
installed and retained to the top front of the intake manifold and sealed by an O-ring seal. The
evaporative (EVAP) emission canister purge solenoid valve is mounted to the fuel rail at the left
front of the intake manifold. There are no coolant passages within the intake manifold.

Oil Pan

The structural rear-sump oil pan is cast aluminum. Incorporated into the design is the oil filter
mounting boss, drain plug opening, baffle, and oil level sensor. The oil filter bypass valve is now
incorporated into the new design oil filter assembly. The oil filter bypass valve is no longer part
of the oil pan assembly as in earlier design applications. The active fuel management oil pressure
relief valve is also internal to the oil pan. Alignment of the structural oil pan to the rear of the
engine block and transmission housing is critical.

Piston and Connecting Rod Assembly

The pistons are cast aluminum. The pistons use 2 compression rings and 1 oil control ring
assembly. The piston is a low friction, lightweight design with a flat or recessed top and barrel
shaped skirt. The piston pins are chromium steel and are a full-floating design. The connecting
rods are powdered metal. The connecting rods are fractured at the connecting rod journal and
then machined for the proper clearance. All applications use a piston with a graphite coated skirt.
The piston and pin are to be serviced as an assembly.

2008 Chevrolet Silverado 1500

2008 ENGINE Engine Mechanical - 4.8L, 5.3L, 6.0L, 6.2L, or 7.0L - Cab & Chassis Sierra, Cab & Chassis Silverado,

Sierra & Silverado

Valve Rocker Arm Cover Assemblies

The valve rocker arm covers are cast aluminum and use a pre-molded silicon gasket for sealing.
Mounted to each rocker cover are the coil and bracket assemblies. Incorporated into the left
cover is the positive crankcase ventilation (PCV) system dirty air passage. Incorporated into the
right cover is the oil fill tube and the PCV fresh air passage.

Valve Train - RPO LY2/LY6/L92

Motion is transmitted from the camshaft through the hydraulic roller valve lifters and tubular
pushrods to the roller type rocker arms. The nylon valve lifter guides position and retain the valve
lifters. The valve rocker arms for each bank of cylinders are mounted on pedestals or pivot
supports. Each rocker arm is retained on the pivot support and cylinder head by a bolt. Valve lash
is net build.

Valve Train - RPO LH6/LMG/LY5/LC9/L76

Motion is transmitted from the camshaft through the hydraulic roller valve lifters and tubular
pushrods to the roller type rocker arms. The nylon valve lifter guides position and retain the valve
lifters. The valve rocker arms for each bank of cylinders are mounted on pedestals or pivot
supports. Each rocker arm is retained on the pivot support and cylinder head by a bolt. Valve lash
is net build. Cylinders 1, 4, 6, and 7 are active fuel management. Refer to Cylinder Deactivation
(Active Fuel Management) System Description.

CYLINDER DEACTIVATION (ACTIVE FUEL MANAGEMENT) SYSTEM DESCRIPTION

System Operation

General Motors Active Fuel Management engine control system has the ability, under certain
light load driving conditions, to provide maximum fuel economy by deactivating 4 of the engines
8 cylinders. The engine will normally operate on 8 cylinders in V8 mode during starting, idling,
and medium or heavy throttle conditions. When commanded ON, the engine control module
(ECM) will direct the active fuel management system and deactivate cylinders 1 and 7 on the left
bank and cylinders 4 and 6 on the right bank, forcing V4 mode. Refer to Lubrication
Description (RPO LY2) or Lubrication Description (RPO LH6/LMG/LY5/LC9) or
Lubrication Description (RPO LY6/L92) or Lubrication Description (RPO L76) and
Cylinder Deactivation (Active Fuel Management) System Description .

Valve Lifter Oil Manifold Assembly

2008 Chevrolet Silverado 1500

2008 ENGINE Engine Mechanical - 4.8L, 5.3L, 6.0L, 6.2L, or 7.0L - Cab & Chassis Sierra, Cab & Chassis Silverado,

Sierra & Silverado

Fig. 31: View Of Engine Oil Flow
Courtesy of GENERAL MOTORS CORP.

The valve lifter oil manifold assembly (1) is bolted to the top of the engine block beneath the
intake manifold assembly. The oil manifold consists of 4 electrically operated and normally-
closed solenoids (2). Each solenoid directs the flow of pressurized engine oil to the active fuel
management intake and exhaust valve lifters (5). The active fuel management oil pressure relief

2008 Chevrolet Silverado 1500

2008 ENGINE Engine Mechanical - 4.8L, 5.3L, 6.0L, 6.2L, or 7.0L - Cab & Chassis Sierra, Cab & Chassis Silverado,

Sierra & Silverado

valve (6), located in the oil pan, regulates engine oil pressure to the lubrication system and the oil
manifold.

When enabling conditions are met for active fuel management operation, the ECM will ground
each solenoid control circuit in firing order sequence, allowing current to flow through the
solenoid windings. With the windings energized, the solenoid valves open and direct pressurized
engine oil through the valve lifter oil manifold into 8 vertical passages in the engine block lifter
valley. The 8 vertical passages, 2 per cylinder, direct pressurized oil to the valve lifter bores of
the cylinders to be deactivated. When vehicle operating conditions require a return to V8 mode,
the ECM will turn OFF the ground circuit for the solenoids, allowing the solenoid valves to
close. When the solenoid valves are closed, remaining oil pressure is exhausted through the bleed
passages of the valve lifter oil manifold into the engine block lifter valley. The housing of the oil
manifold incorporates several oil bleed passages that continually purge trapped air from the
manifold and engine block.

To help control contamination within the active fuel management hydraulic system, a small
replaceable oil filter (4) is located in the valve lifter oil manifold oil inlet passage. The oil
pressure sensor (3) monitors engine oil pressure and provides information to the ECM.

Active Fuel Management Valve Lifters

Fig. 32: Displacement On Demand Valve Lifters

2008 Chevrolet Silverado 1500

2008 ENGINE Engine Mechanical - 4.8L, 5.3L, 6.0L, 6.2L, or 7.0L - Cab & Chassis Sierra, Cab & Chassis Silverado,

Sierra & Silverado