Engine Block
The engine block is the main structural component of an engine. It supports and helps
maintain alignment of internal and external components. The engine block consists of a
cylinder block and a crankcase. An engine block can be produced as a one-piece or
two-piece unit. The cylinder block is the engine component that consists of the cylinder
bore, cooling fins on air-cooled engines, and valve train components, depending on the
engine design. The cylinder bore is a hole in an engine block that aligns and directs the
piston during movement. The bore of an engine is the diameter of the cylinder bore.
The stroke of an engine is the linear distance that a piston travels in the cylinder bore
from top dead center (TDC) to bottom dead center (BDC).
Top Dead Center (TDC) is the point at which the piston is closest to the cylinder
head. Bottom Dead Center (BDC) is the point at which the piston is farthest from the
cylinder head. Displacement (swept volume) is the volume that a piston displaces in an
engine when it travels from TDC to BDC during the same piston stroke. Generally, the
larger the displacement of the engine, the more power it can produce.
An air-cooled cylinder block has cooling fins on the exterior. A cooling fin is an integral
thin cast strip designed to provide efficient air circulation and dissipation of heat away
from the engine cylinder block into the air stream. Fins or vanes increase the surface
area of the cylinder block contacting ambient air for cooling efficiency. Cooling fins cast
into or bolted onto the flywheel act as fan blades to provide air circulation around the
cylinder block and head. Air circulation dissipates heat generated during combustion to
maintain optimum engine temperatures. A crankcase is an engine component that
houses and supports the crankshaft. In a four-stroke cycle engine, the crankcase also
acts as an oil reservoir for lubrication of engine components. The crankcase may be a
part of the engine block or a separate component.
Cylinder Block Configuration
Cylinder blocks have different configurations based on the design of the engine. This
affects the placement of the cylinders, large holes within the cylinder block building for
holding the pistons. Cars typically have between four to eight cylinders in several
different engine designs.
Engine Type
Description
Example
*Inline Engine
Straight row of cylinders
Inline four engine with a
single row of cylinders
**V Engine
Diagonal row of cylinders V6 engine with six
cylinders in a "V" shape
***W Engine
Diagonal and straight
cylinders
V8 engine with three
diagonal engine banks
The number of cylinders affects the performance of the engine. Generally speaking, the
more cylinders an engine has, the greater its power. However, other factors also affect
engine performance, and modern technology even makes the small four-cylinder engine
a powerful contender on the road.
*The straight or inline engine is an internalcombustion engine with all cylinders aligned in one row
and having no offset. Usually found in four, six and
eight cylinder configurations, they have been used
in automobiles, locomotives and aircraft.
** A V engine, or Vee engine is a common configuration for an internal combustion
engine. The cylinders and pistons are aligned, in two separate planes or 'banks', so that
they appear to be in a "V" when viewed along the axis of the crankshaft. The Vee
configuration generally reduces the overall engine length, height and weight compared
to an equivalent inline configuration.
banks resemble the letter W, in
those of a V engine resemble the letter V.
*** A W engine is
a type
of reciprocating
engine arranged
with its cylinders
in
a configuration in
which the cylinder
the same way
Cylinder Sleeves
Cylinder sleeves are hollow metal tubes inserted inside the holes of the cylinder block.
They allow the pistons to slide back and forth with a minimal amount of friction. Dry
sleeves are permanent additions to the cylinder block and used on both new and
reconditioned engines. Once in place, it is impossible to remove. Flanged sleeves, on
the other hand, work like dry sleeves but are replaceable if they become worn.
Pistons
Each piston fits inside a hole within the cylinder block. In a working engine, the piston
moves due to the combustion that occurs in the combustion chamber at the top of the
cylinder. Air mixed with fuel explodes with the ignition of a spark plug. The force of the
explosion drives the piston down into cylinder. As the piston moves, it pulls on the
connecting rod, which attaches the piston to the crankshaft. This basic up and down
motion is the essence of what gives an engine its power. Pistons also use durable
heavy metal materials because they must be strong enough to bear the force of the
explosion, according to CDX Automotive, an online vehicle encyclopedia.
Connecting Rods
In comparison to the large, round pistons, connecting rods are very slender. Their one
and only purpose is to connect the piston to the crankshaft. As the piston moves back
and forth, it turns the crank within the crankshaft via the connecting rod. If the
connecting rod breaks, the crank will not turn and the car will not move even if all of the
pistons fire correctly.
Crankshaft
The bottom portion of the cylinder block consists of the crankshaft, which houses a
large mechanical crank. The up and down motion of the cylinders turn the crankshaft via
the connecting rods, and this provides the engine with its power. An engine's "cycle" is
one complete rotation of the crank within the cylinder block.
