Small Engine Terminology
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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
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.