1. Agricultural Mechanics
Small Gas Engines

2. Terms Four-stroke cycle engine – an engine with four strokes per cycle
Internal combustion engine – a device that converts the energy in fuel into rotating power
Stroke – the movement of a piston from top to bottom or from bottom to top
Top Dead Center (TDC) – position of the piston at its highest point
Two-stroke cycle engine – an engine with two strokes per cycle

3. Uses of Small Gas Engines
Mowers
Trimmers
Chainsaws
Water pumps and wells
4 wheelers
Welders
Generators

4. Parts (Four Stroke Engine)

5. Strokes Of A Four-Stroke-Cycle Engine
Intake – fuel-air mixture is taken into the cylinder.
Compression – fuel-air mixture is compressed.
Power – spark from the spark plug ignites fuel-air mixture causing an explosion in the cylinder.
Exhaust – burnt gases are expelled out of the cylinder through the muffler.

7. Parts (Two Stroke Engine)

8. Strokes Of A Two-Stroke-Cycle Engine
The two-stroke-cycle engine completes the intake, compression, power, and exhaust in two strokes of the piston.
Two stroke engines are lighter weight and can be used at all angles because there is no oil in the engine. Two stroke engines use a fuel-oil mixture.

9. Strokes of a Two-stroke-Cycle Engine

10. Safety Practices For Small Engines
Wear safety glasses and leather shoes.
Keep hands and feet a safe distance from all moving parts.
Do not use flames or sparks near oil, solvents, or gasoline.
Stop the engine and allow it to cool before refueling.
Whenever possible, handle gasoline outdoors.

11. Safety Practices For Small Engines
Disconnect the spark plug before making adjustments or working on the engine.
Never disengage any of the safety equipment or devices.
Keep all shields in place.
Do not overload engines or force equipment beyond the designed capacity.
Never leave engines running indoors.

12. Safety Practices For Small Engines
Never use gasoline as a solvent or to clean engine parts.
Dispose of gasoline, oil, and other solvents properly.
Store gasoline and other fuels in approved containers.
Work in well-ventilated areas.
Keep approved fire extinguishers in the area.