Transcript Small Engines

Small Engines
The identification and
operating process of
four-cycle and twocycle small engines
Mr. Alan Ford
Performance objectives:
Identification of four-cycle engines
Identification of two-cycle engines
Describe the appropriate
operations of these engines
Students will be able to:
 Discuss
the common uses of small
engines
 Distinguish between two-cycle and fourcycle engines
 Identify the major components of small
engines
 Explain the function of the major
components of small engines
Students will be able to:
 Explain
the position of the piston and
valves during each stroke
 Explain what is taking place during each
stroke of four- and two- cycle engines
What are some uses for Small
Engines???
 Chainsaws
 Lawnmowers
 Weed
Eaters
 Go-Carts
 Compressors
 Garden Tillers
There are two different types
of small engines
Four-cycle
Engines
Two-cycle
Engines
We will now discuss each of the engines
The Four-cycle Engine
Lawn Tillers
Go-Carts
Lawn mowers
Compressors
Ect…..
Does anyone know why it is
called a Four-cycle Engine??
A four-cycle engine operates in a series
of four (cycles or strokes) of a piston
moving up and down within the cylinder
of a motor.
Here are pictures of the piston
as well as the cylinder within
which the piston moves up
and down inside
The piston is connected to the
crankshaft, which converts the linear
motion of the piston into the rotary
motion, that powers the implement.

Crankshaft
The crankshaft extends through the
crankcase and is attached to a flywheel
at one end and the implement such as a
blade, pulley, gear, or transmission at the
other end.

crankcase
The crankcase also houses the
camshaft which connects to and
rotates along with the crankshaft.

The camshaft has a
pair of lobes on it
that are responsible
for lifting a set of
valves that controls
the intake and
exhaust operations
of the engine.
The valves which the camshaft lobes
lift are called the Intake and Exhaust
valves. They are located inside the
engine block which also surrounds
the cylinder block
Intake Exhaust
cylinder
The Intake Valve is used to allow air-fuel
mixture to enter into the cylinder area called
the Combustion Chamber.
The purpose of the Exhaust Valve is to allow
the used up air-fuel mixture (exhaust) to
escape out of the Combustion Chamber.

Combustion
Chamber
The block is capped off by a thick
plate of metal called the Head,
which is used to seal off the the
cylinder.
Cylinder Head

The Head is
secured by
numerous
head bolts.
What provides the engine with
an Air-Fuel mixture?

Gas from the fuel
tank enters into the
Carburetor, where
it is then vaporized
and mixed with
right amount of air
needed for
combustion.
What causes the combustion?

Ignition of the airfuel mixture occurs
from an electrical
spark coming from
the Spark Plug. The
result of the burning
gas generates the
force that moves the
piston.
The spark from the spark plug
comes from a process called
electrical induction.

This process starts
at the Flywheel,
which is a circular
piece of metal that
has a magnetic area
located on part of its
circumference.
Electrical Induction continues
as the magnetic area passes
over the Armature.

The armature captures
the low voltage current
produced by the
passing magnet in its
primary coil. When the
circuit is opened it ups
the voltage as the
current passes through
a secondary coil and
onto the spark plug.
In a four-cycle engine, moving
parts are lubricated by motor oil

The oil is located in the bottom of the
crankcase in an area called the oil sump,
where it is distributed through the motor
usually from an oil slinger or a dipper that
splashes the oil around while the crankshaft
rotates
The Strokes of a Four-Cycle Engine
 It
takes four strokes
(movement of the
piston either up or
down inside the
cylinder) to complete
one full cycle of the
engine
1. Intake Stroke
2. Compression
Stroke
3. Power Stroke
4. Exhaust Stroke
Intake Stroke


The piston moves
downward in the
cylinder creating a
vacuum or area of low
pressure.
The rotating camshaft
lifts the intake valve
allowing air-fuel mixture
to enter into the
combustion chamber.
Intake Stroke:

KEY:
A = Intake passage
B = Intake valve
C = Spark plug
D = Exhaust valve
E = Exhaust passage
F = Piston
G = Piston pin
H = Connecting rod
I = Crankshaft
J = Crankcase
K = Combustion chamber
Compression Stroke

The piston moves
upward in the
cylinder, compressing
the air-fuel mixture
between the top of
the piston and the
cylinder head. That
is the area called the
combustion chamber.
Compression Stroke:

KEY:
A = Intake passage
B = Intake valve
C = Spark plug
D = Exhaust valve
E = Exhaust passage
F = Piston
G = Piston pin
H = Connecting rod
I = Crankshaft
J = Crankcase
K = Combustion chamber
Power Stroke

The spark plug fires
and ignites the
compressed air-fuel
mixture
 The expanding gas
formed forces the
piston back
downward
 Both valves continue
to remain tightly
closed
Power Stroke:

KEY:
A = Intake passage
B = Intake valve
C = Spark plug
D = Exhaust valve
E = Exhaust passage
F = Piston
G = Piston pin
H = Connecting rod
I = Crankshaft
J = Crankcase
K = Combustion chamber
Exhaust Stroke



The piston begins
moving back upward
The exhaust valve is
lifted open by the
exhaust lobe on the
camshaft
The exhaust fumes are
forced out of the
cylinder past the
exhaust valve and out
of the engine through
the muffler
Exhaust Stroke:

KEY:
A = Intake passage
B = Intake valve
C = Spark plug
D = Exhaust valve
E = Exhaust passage
F = Piston
G = Piston pin
H = Connecting rod
I = Crankshaft
J = Crankcase
K = Combustion chamber
The Start of a New Cycle
Once the piston finishes the
Exhaust Stroke and reaches the
top of the cylinder, the Intake Valve
begins to open as the piston moves
downward, starting the Intake
Stroke and beginning the whole
process once again.
Two-Cycle Engines
Two-Cycle Engines
 They
are generally used for smaller,
hand held equipment like chainsaws
and weed eaters because than can be
smaller and lighter weight.
 They are also unique because, unlike
four-cycles, they can be used while on
their sides and up-side down.
Two-Cycle Engines
 These
engines complete all the cycles
of intake, compression, power, and
exhaust in only two strokes of the
piston.
 The crankshaft only has to make one
full rotation to complete a two-stroke
cycle before beginning again.
The Operation of a Two-Cycle
The Operation of a Two-Cycle
The Operation of a Two-Cycle
Unique Features of a Two-Cycle

Two-Cycle engines
do not have valves
like the four-cycles.
 They have an
Exhaust Port for the
emissions and a
Reed Valve for the
air-fuel mixture to
enter in past.
Unique Features of a Two-Cycle



These engines do not
have an oil sump.
The oil needed for
lubricating moving parts
comes from the oil-gas
mixture it is required to
use.
This is why the motor
does not have to remain
upright for operations.
Summary




With the piston moving down, air/fuel mixture
from the carburetor enters the combustion
chamber through the intake valve.
An electrical charge induced from the magnet on
the flywheel is picked up by the armature and is
sent to the spark plug which ignites the mixture.
The burning gases drive the piston downward
while both valves are closed creating the power.
The piston is connected to a crankshaft which
converts the up and down motion of the piston to a
rotary motion which drives the implement.
Summary
 The
crankshaft is responsible for turning
the camshaft, the flywheel, and the
lubrication system.
 The Lobes on the camshaft are
responsible for lifting the Intake and the
Exhaust valves at the appropriate times.
 As the piston moves back upward the
exhaust valve opens and lets the fumes
escape the combustion chamber.
Summary
 The
2-cycle engines undergo the same
events of intake, compression, power,
and exhaust, but only takes 2 piston
strokes to complete the cycle.
 Two-cycle engines have the oil needed
for lubrication of moving parts mixed in
with the fuel. There is not a need for an
oil sump and can be used up-side down