Small Engine Theory What is the purpose of a Small Engine? When does a small engine Get classified...
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Transcript of Small Engine Theory What is the purpose of a Small Engine? When does a small engine Get classified...
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Small Engine Theory
What is the purpose of a Small Engine?When does a small engine Get classified into a large engine?
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Internal Combustion Engine
Internal: To happen inside Combustion: Burning of some sort of fuel and
air. Engine: Converts heat energy into a useful
mechanical energy.
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Four Main Parts
Piston
Connecting Rod
Cylinder
Crankshaft
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Piston
A plunger that slides in the cylinder converting heat energy into mechanical energy
Light weight material (Aluminum alloy) so it can spin at high revolutions per minute.
Must withstand pressures up to 2,000PSI Must withstand heat up to 1,200 F Must not expand
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Connecting Rod
Used to connect the piston to the crankshaft I-Beam construction, saves weight and
makes the rod stronger. Connecting rod cap is bolted to the end with
the use of two hardened bolts. Piston pin connects piston to the connecting
rod
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Cylinder
Made from Aluminum alloy or Cast iron
TWO PARTS OF THE CYLINDER ARE: Cylinder Head Cylinder Block
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Cylinder Head
Houses the combustion chamber and the spark plug.
I-Head (OHV) Houses:all the above plus valves, seats, valve guides, intake and exhaust ports, rocker stud, pushrod guide plate.
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Cylinder Block
The foundation for all moving parts. Houses the cylinder: the area the piston
moves up and down in. Houses the crankshaft Makes-up the crankcase, area where the
crankshaft rotates. Houses the following in a L-head engine;
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Valves Valve Seats Intake and Exhaust Ports Valve Springs and Retainers Tappets Camshaft
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Crankshaft
Made of nodular steel. Changes Reciprocating motion into rotary
motion. Parts
PTO JOURNAL ROD JOURNAL MAGNETO JOURNAL COUNTER-WEIGHTS
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FLYWHEEL
Carries the crankshaft through the three non power producing strokes.
A heavy weight; takes a lot of energy to start and stop
Provides the crankshaft with inertia.
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COMBUSTION CHAMBER
Area in the cylinder head where fuel and air are burned.
Spark plug is always located in the combustion chamber.
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Fuel
A combustible that will burn effectively in the combustion chamber
Types Gasoline (petro) Diesel Propane Compressed natural gas
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Fuel Stages
Liquid Purchased and delivered to the carburetor in this
state. Atomized
Carburetor mixes with air in this state. To the proper stochiometric ratio of 14:1 air to fuel
Vaporized Fuel becomes a gas in the combustion chamber
on the compression stroke
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Valve train
All components that allow for the transfer of fuel and air both fresh and burnt.
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Valves
Open and close the combustion chamber. Seals the combustion chamber. Allows for the transfer of fuel and air.
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Valve seats
Inserts in the block or head that allow the valves face to rest on, and to cool and seal the combustion chamber.
Made from high carbon steel to withstand high heat and pressure.
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Valve guide
Tube like structure in the head or block that guides the valve, and is concentric with the valve seat.
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Valve spring
Used to keep the valve closed.
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Valve Retainers
Used to retain the valve spring onto the valve.
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Camshaft
Used to open and close the valves at the proper time (phasing), for a specific length of time (duration).
Driven by the crankshaft. Gear, chain or belt driven
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Tappets/ Lifters
Used to transfer the motion of the camshaft to the valve (L-head) or the push-rod (ohv)
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Passageways
Fuel and Air must pass into and out of the combustion chamber.
Fresh fuel and air is called INTAKE
Burnt fuel and air is called EXHAUST
Cylinder head passageways are called PORTS
MANIFOLD passageways are called RUNNERS
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Four stroke cycle
IntakeCompression
PowerExhaust
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Intake stroke
Piston moves down from TDC to BDC.
Cylinder creates a vacuum.Fuel and Air rush into the cylinder
when the Intake Valve opens.Cylinder is now filled with the
fresh fuel and air charge.Exhaust valve stays closed.
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Compression
Piston moves from BDC to TDC.
Fuel and Air is squeezed so tight that heat is generated.
Fuel becomes Vaporized.Intake and Exhaust valves
are closed.
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Power
Piston moves from TDC to BDC.Fuel and air is Ignited by the
spark plug.Fast burning of the fuel creates a
tremendous heat and pressure increase.
Pressure forces the piston down with 2000 PSI of Force.
Both the Intake and Exhaust valves are closed.
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Exhaust
Piston moves from BDC to TDC Exhaust valve opens, Intake stays closed Burnt fuel and air is forced out of the exhaust
Ports and exhaust manifold Runners.
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Four stroke cycle
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HEAD AND BLOCK
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CLYINDER BLOCKS
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ALUMINUM BLOCKS
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CYLINDER SLEEVES
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GREY IRON
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CYLINDER HEADS
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Alloys
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RECIPROCATING
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PISTONS RINGS AND RODS
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PRESSURE AND TEMPERATURE
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PRESSURE AND VOLUME
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ENERGY
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CAMSHAFT
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CAM PHASING
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COMBUSTION CHAMBER
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TURBULANCE
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GASKETS