1. Systems
of the
Engine

2. Compression System
-Upward movement of piston in the cylinder (compression stroke) compresses the gases into the combustion chamber at the top of piston.
-Downward movement of piston (power stroke) turns crankshaft and creates power for engine
-Compression is usually lost in 1 of 3 places:
- the fit of the piston in the cylinder
- a bad head gasket
- valves that close improperly

3. Fuel System
Consists of the fuel tank, fuel lines, carburetor, and intake system
As piston moves down cylinder on intake stroke, a vacuum is created that pulls through the intake valve and through the carburetor
As air is drawn in, it passes through restrictions in throat of carburetor called venturi and creates a low pressure area that makes air come through more rapidly
Valves are opened and closed by a lobed rod called a camshaft. It is timed to open and close valves at a precisely correct time.
To prevent the engine from running too fast, a governor is attached to carburetor that slows engine when a certain speed is reached.

4. Ignition System
When fuel mixture has entered the combustion chamber and been compressed, a spark must occur for fuel to ignite
Most small gas engines have an ignition system called a magneto in which a spark is created by electrical current generated by process called electrical induction. A low-voltage current is generated when a strong magnet located in flywheel passes very close to armature coil.
Spark plug consists of 2 parts:
Center electrode that runs length of middle of plug
Ground electrode that’s grounded to the block of the engine

5. Cooling System
A small engine can fire and ignite fuel mixture over 2,000 times per minute.
Heat generated by combustion can be as much as 3,000 degrees F
Fins on flywheel serve as a fan to move air across and around engine

6. Lubricating System
It’s essential oil is circulated to all internal parts within the crankcase.
Oil serves 4 purposes:
1.) lubricates moving parts
2.) cleans engine
3.) movement of liquid oil helps to cool interior of engine
4.) oil helps to seal gap between rings and cylinder wall