Small Engine Terminology
Performance Objectives:
 Students will be able to define, recognize, and
utilize terms concerning small engines
effectively.
Enabling Objectives
 Students will define small gas engine terms.
 Students will use correct terminology in
discussion of small engines.
 Students will recognize small gas engine
terminology and be able to effectively apply
terms to usage and maintenance of the engine.
“How does this whachamacallit fit into
the whozamathingy?”
“I need a flappy white thing that goes
on the top of the engine.”
“ Effectively communicating your
intentions is a key point to success.
Terminology is the key!”
Small Engine Maintenance
 Internal Combustion Engine-
Device that
burns fuel inside a cylinder to create a force
that drives a piston.
 Piston- A sliding cylinder fitting within a
cylindrical vessel that receives the force of
combusting fuel.
 Crankshaft- A shaft with an offset projection
that converts circular motion to reciprocal
motion, or vice versa.
 Reciprocating- return; move back and forth
 Horizontal shaft engine-
An engine with a
crankshaft that lies crossways for normal
operation
 Vertical shaft engine- an engine whose
crankshaft is vertical for normal operation
 Stroke- the movement of a piston from top to
bottom or from bottom to top
 Cycle- All the event that take place as an
engine takes in air and fuel, compresses the
air fuel mixture, burns the fuel, and expels
the burned gasses. Also the current
produced by one turn of a generator
armature.
 Four- stroke cycle-
four strokes per cycle
 Two-stroke cycle- two strokes per cycle
 Poppet valve- a valve that controls the flow
of air and gasses by moving up and down.
 Port- a special hole in the cylinder wall of a
two cycle engine to permit gasses to flow in
or out of the cylinder.
 Reed valve- a flat, flexible plat that permits
air or liquid to pass on one direction but
seals when the flow reverses.
 Intake stroke- engine process of taking fuel
and air into the combustion chamber
 Compression stroke- Movement of an engine
piston to squeeze or compress the air-fuel
mixture
 Compression ratio- the relationship between
the volume of an engine cylinder at the
beginning and end of the compression
stroke.
 Top Dead Center (TDC)- position of a piston
when at its highest point (furthest from the
crankshaft)
 Bottom Dead Center (BDC)-
piston at its
lowest point ( point nearest the crankshaft)
 Fire- flame; to make a spark jump across an
air gap
 Ignition- a spark igniting an air-fuel mixture
 Power stroke- the engine process in which
burning fuel expands rapidly but evenly to
drive the piston down
 Exhaust- burned gasses removed by the
motion of a piston
 Exhaust Stroke-
Movement of a piston which
expels burned gases from a cylinder
 Revolution- one complete turn of 360
degrees
 Momentum- turning force of the flywheel and
other moving parts that carries an engine
through nonpower strokes.
 Maintenance- doing the tasks that keep a
machine in good condition
 Troubleshooting- determining what causes a
malfunction in a machine or process.
 Repair- to replace a faulty part or make it
work correctly.
 Adjust- to set a part or parts to function as
designed.
 Contaminant- any material that does not
belong in a substance
 Saturate- to add a substance until the excess
starts to run out.
 Dual-two
 Precleaner- a device that removes large
particles from air entering an air cleaner
 Shroud- to cover; a cover
 Score- to scratch
 Torqued- A twisting force; to twist
 Speed indicator- a device used to measure
revolutions per minute (RPM) of a turning
shaft or part.
 RPM-revolution per minute
 Leaner-
a greater proportion of air and lesser
proportion of fuel in an air-fuel mixture.
 Richer- a mixture with an increased
proportion of fuel to air
 Labor- to struggle or work hard to keep
running
Small Engine Adjustment and
Repair
 Overhaul- complete disassembly with
cleaning and reconditioning or replacement
of most moving parts.
 Governor- Speed control device
 Air Vane- type of governor used on small
engines
 Carburator- Provides fuel and air to the
engine in appropriate portions and volume.
 Needle- A long tapered shaft
 A hole shaped to receive the needle and
control the flow of fuel.
 Jet or Seat- a hole shaped to receive the
needle and control the flow of fuel.
 Battery- produces electricity by chemical
action.
 Magneto- produces electricity by magnetism
 Condensor- stores and releases current to
boost current in the Primary circuit
 Primary circuit-
low-voltage circuit of an
ignition system
 Secondary circuit- high-voltage circuit of an
ignition system.
 High-tension wire- high voltage wire in a
secondary circuit
 Electromagnetic induction- conversion of
low-voltage current to high-voltage current
with a coil.
 Ignition spark- hot electrical arc across an
air gap
 Ignition points-
interrupt the flow in the
primary circuit at the correct time to induce
the high voltage flow to the spark plug.
 Discharge- loss of power from a battery
 Electrolyte- acid solution in a battery
 Distilled water- free of iron or other parts
 Armature- the rotating part of a motor. Also
the iron core portion of a magneto.
 Head gasket- seal between the head and the
cylinder block
 Valve Spring Compressor-
compresses the
valve spring to remove keepers.
 Valve keeper- transfers spring force to valve
stem
 Stem- long, round section of a valve
 Margin- outer edge of a valve head
 Face- surface that is intended for use. Also
tapered section of a valve head.
 Lapped in- grinding valves to fit the seat for
a perfect seal
 Lapping compound- gritty material used for
lapping in valves
 Valve grinding- the process of grinding
valves
 Valve guide- holds valve stem in alignment
 Valve stem clearance- air gap between valve
and push rod.
 Cylinder- engine cavity containing a piston
 Head- flat part of a valve; cylinder cover
containing the spark plug and combustion
chamber.
 Piston- a sliding cylinder fitting within a
cylindrical vessel that receives the force of
combusting fuel.
 Rings- complete the seal between the piston
and cylinder wall.
 Inside micrometer- telescoping gauge used
to measure inside surfaces of hollow objects.
 Telescoping gauge- inside micrometer
 Cylinder hone- Tool for restoring cylinders
 Ring expander-
tool used to remove and
install piston rings
 Blow-by- compression leakage past pistons
 Piston ring compressor- used to force piston
rings into their grooves
 Wrist pin (Crank pin)- pin between a
connecting rod and piston
 Micrometer- Used to measure outside
surfaces of round objects
 Plastigage- carefully designed material that
flattens out uniformly when pressed.
 Rope starter-
rope wrapped around a pulley
for turning power to start an engine
 Wind up starter- uses a lever to coil a
spring for cranking an engine.
 Valve pin- Transfers spring force to valve
stem
 Head- flat part of a valve; cylinder cover
containing the spark plug and combustion
chamber.
Vocabulary Quiz
1.
2.
3.
4.
5.
Burned gases removed by the motion
of the a piston.
The movement of a piston from top to
bottom or from bottom to top.
A sliding cylinder fitting within a
cylindrical vessel that receives the
force of combusting fuel.
The engine process in which burning
fuels expands rapidly but evenly to
drive the piston down.
Movement of a piston which expels
burned gases from a cylinder.
A.
B.
C.
D.
E.
Exhaust stroke
Power Stroke
Piston
Stroke
Exhaust
6.
7.
8.
9.
10.
11.
Doing the tasks that keep a machine
in good condition.
Engine process of taking fuel and air
into the combustion chamber
Movement of an engine piston to
squeeze or compress the air-fuel
mixture.
A spark igniting an air-fuel mixture
Turning force of the flywheel and
other moving parts that carries an
engine through nonpower strokes.
To replace a faulty part or make it
work correctly
A.
B.
C.
D.
E.
F.
Repair
Momentum
Intake stroke
Ignition
Compression
Stroke
Maintenance
Determining what causes a
malfunction in a machine or process.
13. All the events that take place as an
engine takes in air and fuel,
compresses the air-fuel mixture,
burns the fuel, and expels the
burned gases.
14. Device that burns fuel inside a
cylinder to create a force that drives
a piston.
15. A shaft with an offset projection that
converts circular motion to reciprocal
motion, or vice versa.
12.
Crankshaft
B. Troubleshooting
C. Cycle
D. Internal
Combustion
Engine
A.
16.
17.
18.
19.
20.
21.
Provides fuel and air to the
engine in appropriate portions
and volume.
Produces electricity by
magnetism
The rotating part of a motor.
Seal between the head and the
cylinder block
Complete the seal between the
piston and the cylinder wall.
Stores and releases current to
boost current in the Primary
circuit.
A.
B.
C.
D.
E.
F.
Head gasket
Armature
Condensor
Magneto
Carburetor
Rings
21.
22.
23.
24.
25.
Used to measure outside
surfaces of round objects.
Inside Micrometer
Flat part of the valve
A twisting force
Compression leakage past
pistons
A.
B.
C.
D.
E.
Telescoping
gauge
Blow-by
Torque
Head
Micrometer