1. SMALL ENGINES
ENGINE
OPERATION FOR
A FOUR STROKE
ENGINE

2. SMALL ENGINES
An engine is a device which converts energy into mechanical motion to do work.
Small engines are described as internal combustion engines rated up to 25 horsepower.
A small engine has either a spark ignition or a compression ignition based on how the fuel is ignited.
Small engines are classified as either four-stroke cycle engines or two-stroke cycle engines.

3. PARTS OF THE ENGINE CYLINDER BLOCK
Engine component which consists of the cylinder bore, cooling fins, and valve train components. Made of cast aluminum alloy that are lightweight and dissipate heat rapidly.
CYLINDER HEAD
Engine component made out of cast aluminum alloy fastened to the end of the cylinder block farthest from the crankshaft.
COOLING FINS
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.
HEAD GASKET
A filler material placed between the cylinder block and cylinder head to seal the combustion chamber. Made of soft metals and graphite layered together.
SPARK PLUG
Component that isolates the electricity and produces the spark for the engine

4. PARTS OF THE ENGINE PISTON
A cylindrical engine component that slides back and forth in the cylinder bore by forces produced during the combustion process.
CONNECTING ROD
Engine component that transfers motion from the piston to the crankshaft and functions as a lever arm.
CRANKSHAFT
An engine component that converts linear (reciprocating) motion of the piston into rotary motion.
FLYWHEEL
A cast iron disk that is mounted at one end of the crankshaft to provide inertia for the engine.
COUNTERWEIGHTS
A protruding mass cast into the crankshaft which partially balances the forces of a reciprocating piston.

5. PISTON PARTS OF THE ENGINE
A cylindrical engine component that slides back and forth in the cylinder bore by forces produced during the combustion process.

6. PISTON PARTS OF THE ENGINE DIFFERENT PISTON TYPES: FLAT DOMED
IRREGULAR
DISHED

7. PISTON PARTS OF THE ENGINE
PISTON RINGS:
An expandable split ring used to provide a seal between the piston and the cylinder wall
Three types:
COMPRESSION RING
WIPER RING
OIL RING 1 2 3

8. VALVE TRAIN PARTS OF THE ENGINE VALVE HEAD MARGIN VALVE FACE
VALVE SEAT
VALVE NECK
VALVE GUIDE
VALVE SPRING
VALVE ROTATOR
VALVE SPRING RETAINER

9. INTAKE STROKE COMPRESSION STROKE POWER STROKE EXHAUST STROKE
FOUR STROKE CYCLE ENGINE
INTAKE STROKE
COMPRESSION STROKE
POWER STROKE
EXHAUST STROKE

10. INTAKE STROKE Occurs from TDC to BDC Intake valve opens
Air-Fuel that was previously mixed in the carburetor is now sucked into the combustion chamber due to the low pressure created inside.

11. COMPRESSION STROKE Compresses the Air-Fuel mixture
By compressing the Air-Fuel mixture:
Allows for more energy to be released.
Increases fuel vaporization
Allows for more complete burning

12. POWER STROKE Spark occurs igniting compressed air-fuel mixture
Spark occurs 20 degrees before TDC so the flame front can spread throughout combustion chamber
Gases ignite pushing piston away from the cylinder head
Linear motion from the piston is transferred into a rotary motion on the crankshaft

13. EXHAUST STROKE Exhaust valve opens
Inertia from the flywheel and other parts push the piston back up toward TDC, pushing the spent gases out of the combustion chamber.

14. THE END