TYPES OF SMALL ENGINES

• Two stoke- two cycle engine

• Four stroke- four cycle engine

• Stroke= movement of the piston within the cylinder

TWO STROKE ENGINES

• Two stroke advantages• Don’t have valves• Quick power- fire every revolution• Lighter/cheaper• All orientations- no issue with oil delivery

• Two stroke disadvantages• No lubrication system- shorter life• Expensive oil/less efficient fuel

FOUR STROKE ENGINES

• Four stroke advantages• More power• Longer lasting• More efficient with fuel/oil

• Four stroke disadvantages• Complicated• Heavy• More expensive• Limited orientation

BASIC CYCLES OF A 4 STROKE

• Intake- piston goes down, valves open • Goal: Air/fuel mixture enters cylinder

• Compression- piston heads up, valves close• Goal: Creates pressure

• Power- piston pushed down, valves closed• Goal: Spark ignites gases

• Exhaust- piston moves up, valves open• Goal: Exhausted mixture pushed out of engine

• Repeat!

IGNITION SYSTEM

PURPOSE

• Produce a spark within the spark plug • Ignites air/fuel mixture

• Timing is essential

ELECTRON THEORY

• Electrons travel in orbits around the center of an atom

• Electrons carry a negative charge• Protons carry a positive charge• Neutrons carry no charge

• Conductors allow electrons to move from one atom to another easily.

• Electrons travel when a circuit is complete & there is a difference in charge

PRODUCING ELECTRICITY

• Mechanically- generator run by water• Chemically- batteries• Statically- lightning

MEASURING ELECTRICITY

• Amperes- rate of electron flow• Volts- force that causes electrons to flow• Ohm’s- resistance to electron flow

MAGNETS & ELECTRICITY

Magnets have north & south polesOpposite attract

Magneto system- Electricity can be made through magnets

MAGNETO SYSTEM

• Armature the armature is shaped like a capital "U". The two ends of the U point toward the flywheel.• A primary coil of perhaps 200 turns of thick wire

wrapped around one leg of the U• A secondary coil of perhaps 20,000 turns of very

thin wire wrapped around the primary coil• Breaker points• A pair of strong permanent magnets embedded in

the engine's flywheel.

STEPS IN MAGNETO SYSTEM

• 1. Magnets fly past the U-shaped armature, • Creates a magnetic field• Small amount of current in coils

• A breaker point opens. This switch breaks the flow of current through the primary coil and causes a voltage spike (of perhaps 200 volts). The secondary coil, having 100 times more turns than the primary coil, amplifies this voltage to approximately 20,000 volts

• Sparks instant that breaker point opens

SPARK PLUG

• Center electrode- runs through middle• Carries high voltage current to the spark gap.• Jumps gap• Creates spark• Ignites air/fuel mixture