1. Ag Science and Tech
Small Gas Engines

2. Objectives
Understand correct safety procedures when working with small gas engines in the shop.
Identify tools used when working with small gas engines.
Describe the strokes of 2-stroke and 4-stroke engines.
Define the components of a small gas engine and their functions.

3. Terms Engine Internal combustion engine Piston Piston rings
Connecting rod
Crankshaft
Crankcase
Valves
Intake valve
Exhaust valve
Valve lifters
Cylinder head
Camshaft
Carburetor
Flywheel
Spark plug

4. Internal combustion engine
Function of engines
Engine
A device for converting chemical energy into mechanical energy.
Internal combustion engine
Device that burns fuel inside a cylinder to create a force that drives a piston.

5. Safety Safety glasses must be worn at all times.
Keep hands and feet away from all moving parts during operation.
Keep all ignition sources away from the work area.
Stop engine and allow it to cool before refueling.
Handle gasoline outdoors if possible.
Disconnect the spark plug lead when making adjustment to prevent accidental start-up.
Never disengage any of the safety equipment or devices.

6. Safety Keep all shields in place.
Do not operate engines above the specified speed.
Never overload engines or force equipment beyond it the designed capacity.
Never use gasoline as a solvent to clean parts.
Only start and run engines where ventilation is adequate, preferably outdoors.
Never pour gasoline or oil on the ground or down a drain, dispose of it in the correct container to be recycled.

7. Engine components Piston Crankshaft Crankcase Valves Camshaft Cylinder
Cylinder head
Carburetor
Flywheel
Spark plug

8. piston Located in the cylinder
Piston rings- an expanding ring placed in the grooves of the piston to seal it against the passage of fluid or gas.

9. Connecting rod
Piston is connected to the crankshaft by the connecting rod.

10. Crankshaft
Converts up and down motion into rotating force.

11. crankcase Holds the crankshaft in place.
Also houses the camshaft and oil.

12. Valves Intake valve Exhaust valve Valve lifters
Allows air/fuel mixture to enter the combustion chamber.
Exhaust valve
Allows fumes to exit the cylinder.
Valve lifters
Moves the valves up and down
Powered by the camshaft

13. Camshaft Operates opening and closing of the valves.
Rotated by a gear on the crankshaft.

14. cylinder Combustion chamber Where the piston is located
Cylinder head- seals the cylinder

15. Carburetor
Mixes air and fuel before it is pulled into the combustion chamber.

16. flywheel
Turned by crankshaft to induce electrical current with magnet through the magneto.
Momentum

17. Spark plug
Supplies spark.

18. 2-stroke engines
Combustion
Compression

19. 4-stroke engines
Intake
Compression
Power
Exhaust

20. Classifying engines 2- or 4-stroke Amount of power they produce
<25 hp = small engine
>25 hp = large engine
Number of cylinders
Single-cylinder
Multi-cylinder

21. Classifying engines Engine displacement Cylinder arrangement Fuel
Total swept volume of the engine cylinders as the piston completes one stroke.
Cylinder arrangement
In-line
Vee-block
Fuel
Gasoline
Diesel

22. Micrometer

23. Inside micrometer

24. feeler gauges

25. Spark plug gap

26. Torque wrench

27. Compression gauge

28. Telescoping gauge