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Cylinder Block / Lost Foam Casting Process
Technical 2
August 2000
Cylinder Block / Lost Foam Casting Process
The all-aluminum cylinder block construction features a deep skirt design and is lighter than
conventional cast iron truck engines. The premium A356 aluminum primary material is used with
a T6 heat treatment to provide the strength requirements of a truck engine. This material is very
similar to the aluminum used in wheels. The engine block and cylinder head are cast using
General Motors lost foam process. It offers a number of environmental benefits when compared
to conventional casting.
GM pioneered lost foam cylinder block casting in 1982, and has continuously refined the process.
The process begins with a styrofoam assembly that replicates the part being cast. Loose sand is
poured around the assembly and shaken into its voids. Molten aluminum is then poured through
a foam sprue into the sand where the hot metal melts the foam, displaces it and cools in the shape
of the part.
Unlike conventional casting, the lost foam process allows passages and other features to be cast
directly into the part. Oil galleries, ventilation and oil drain back passages (which keep oil away
from the crank) are cast into the block. Coolant passages, which would otherwise require drilling
or external plumbing (with a potential for leaks) are also cast into the block. This results in less
machining and fewer opportunities for error. Technical 3
August 2000
Another benefit of the lost foam process is that it allows narrow water jacket passages, which keep
coolant velocities high. In addition, the lost foam process allows for a coolant jacket design that
sweeps coolant in and out of the siamese region. The detailed design of the coolant jacket was
optimized extensively using computational fluid dynamics. The result is a low volume coolant
jacket that warms up quickly, yet provides cooling for 90 percent of the stroke, with even heat
transfer.
This engine features pressed in cast iron liners. The installation process includes chilling the liner
prior to placement and sophisticated precision force monitoring to insure proper installation.
The press-fit, ground outside diameter of the liner against the precision bored aluminum cylinder
provides optimal heat transfer. After installation, the iron liner is bored to a mass saving 1.5 mm
wall thickness.
The sand used in conventional casting, typically seen heaped in large mounds outside of
foundries, requires a binder and must be disposed of in landfills. The sand used in lost foam
casting requires no binder and can be used again. Landfill waste is minimized. There is a
substantial reduction in raw material disposed of and used. Crank Bearing Structural Ladder
A bearing beam or ladder connects the seven main powder-metal bearing caps, stiffening the
engine blocks structure. The deep skirt cylinder block design contributes to the increase in
structural stiffness, which reduces overall engine vibration and noise. The beam offers many
advantages of a separate cast lower crankcase with less manufacturing complexity and less
potential for oil leaks.
Technical 4
August 2000 Crankshaft
Designing the Vortec inline six-cylinder crankshaft was a challenging process because of its
length and natural tendency to twist. Thorough engineering was required to ensure quiet
operation, durability, and long-term reliability. Math-based computer tools were utilized to
optimize the design and accelerate the pace of development. Durable nodular iron was selected as
the crankshaft raw material, due to its superb material properties and manufacturability.
The crankshaft length and stroke can drive significant torsional vibration, a wave of flexing, from
one end of the shaft to the other. The torsional vibration challenge was solved by using 70mm
diameter main bearings, minimizing the crankshaft polar mass moment of inertia with an
optimized counterweight design and adding a dual-frequency harmonic damper. The damper
consists of a steel ring and a steel disk which are bonded to the hub, with injection molded
premium rubber inserts of different thickness. It attaches directly to the front of the crank to
counteract the inherent flex and greatly reduces the vibration. The damper is retained to the
crankshaft with a hardened 16mm bolt and a press fit to the crankshaft.
Technical 5
August 2000 Flexplate / Flywheel
The flexplate is the link that transfers power from the engine to the automatic transmission. It is
attached to the crankshaft with eight bolts. A hardened steel retainer plate, in the center of the
flexplate, adds strength and maximizes robustness of the mounting surface. The single-piece
flexplate material is roll-formed steel. Gear teeth are hobbed and flame hardened at the flexplate
perimeter to allow the starter motor engagement to start the engine. By using blind threaded holes,
the potential for oil leaks are eliminated at the crankshaft flange.
The manual flywheel is attached to the crankshaft with eight bolts. The flywheel material is
durable nodular iron with a pressed-on steel flame hardened ring gear that engages with the starter
motor to start the engine. Since the crankshaft is internally balanced, a symmetrical bolt pattern
is used at the crankshaft flange and no external counter weighting is required with the flywheel.
Technical 6
August 2000
Flexplate
Flywheel Piston / Connecting Rods
The piston, found inside the cylinder bore of an engine block, transfers energy through the
connecting rod to the crankshaft. Pistons are made of hyper-eutectic aluminum alloy. Surrounding
the piston are piston rings. They seal the piston in the cylinder bore to control compression of
air/fuel and flow of oil.
The piston features a short 3mm top ring land height, reducing the hydrocarbon crevice. The top
ring is a moly filled, barrel faced steel ring, with a 1.2mm thick iron second ring. The engine
features a full floating piston pin, riding in a bronze connecting rod bearing.
The distance a piston travels is called the stroke. From the bottom to the top of a stroke there is a
change in volume; that change is referred to as the compression ratio (10:1).
The connecting rod connects the piston at one end, with a free floating wrist pin, to the crankshaft
at the other end. The rod is steel, formed from powder metal, and hot forged. The rod is machined
and then the cap is fractured from the rod portion. This fracture joint is used to accurately position
the cap to the rod during engine assembly. Rod bearings are installed into the crankshaft end of
the connecting rods. They provide a smooth surface for the connecting rods to rotate on the
crankshaft. The bearings, sometimes called inserts, are made of steel with an aluminum alloy
bearing surface, using a cladding process to the steel backing to provide the appropriate wear
surface.
An arrow on top of the piston identifies how to install the piston for correct pin offset. The arrow
always points toward the front of the engine.
Technical 7
August 2000 Cylinder Head
Dual overhead camshafts with four valves per cylinder and roller-follower valve actuation can be
found on some premium passenger car engines, but are still rare in trucks. The cylinder head
contributes to the engines overall smoothness and high output. Overhead cams are one of the
most direct, efficient means of operating the valves, while four valves per cylinder improves the
flow of air in and out of the engine. Roller followers create less friction than conventional valve
lifters. The lower friction improves fuel economy.
Compression ratio is important for both torque and horsepower output, as well as fuel economy.
The combustion chamber and cooling system design used on this engine provides for a high
(10:1) compression ratio. Typically, this high compression ratio would require high-octane
gasoline to produce maximum power, or to avoid the hard knocking sound known as detonation.
However, this engine was designed to maximize fuel economy and it does premium gasoline is
not needed. Customers can use regular, unleaded fuel and benefit from the high horsepower this
engine provides. The intake port and combustion chamber configuration provides exceptional air
flow capability and provides appropriate