1. Small Engine Theory What is the purpose of a Small Engine?
When does a small engine Get classified into a large engine?

2. Internal Combustion Engine
Internal: To happen inside
Combustion: Burning of some sort of fuel and air.
Engine: Converts heat energy into a useful mechanical energy.

3. Four Main Parts
Piston
Connecting Rod
Cylinder
Crankshaft

4. Piston
A plunger that slides in the cylinder converting heat energy into mechanical energy
Light weight material (Aluminum alloy) so it can spin at high revolutions per minute.
Must withstand pressures up to 2,000PSI
Must withstand heat up to 1,200 F
Must not expand

5. Connecting Rod Used to connect the piston to the crankshaft
I-Beam construction, saves weight and makes the rod stronger.
Connecting rod cap is bolted to the end with the use of two hardened bolts.
Piston pin connects piston to the connecting rod

6. Cylinder Made from Aluminum alloy or Cast iron
TWO PARTS OF THE CYLINDER ARE:
Cylinder Head
Cylinder Block

7. Cylinder Head Houses the combustion chamber and the spark plug.
I-Head (OHV) Houses:all the above plus valves, seats, valve guides, intake and exhaust ports, rocker stud, pushrod guide plate.

8. Cylinder Block The foundation for all moving parts.
Houses the cylinder: the area the piston moves up and down in.
Houses the crankshaft
Makes-up the crankcase, area where the crankshaft rotates.
Houses the following in a L-head engine;

9. Valves
Valve Seats
Intake and Exhaust Ports
Valve Springs and Retainers
Tappets
Camshaft

10. Crankshaft Made of nodular steel.
Changes Reciprocating motion into rotary motion.
Parts
PTO JOURNAL
ROD JOURNAL
MAGNETO JOURNAL
COUNTER-WEIGHTS

11. FLYWHEEL
Carries the crankshaft through the three non power producing strokes.
A heavy weight; takes a lot of energy to start and stop
Provides the crankshaft with inertia.

12. COMBUSTION CHAMBER
Area in the cylinder head where fuel and air are burned.
Spark plug is always located in the combustion chamber.

13. Fuel
A combustible that will burn effectively in the combustion chamber
Types
Gasoline (petro)
Diesel
Propane
Compressed natural gas

14. Fuel Stages Liquid Atomized Vaporized
Purchased and delivered to the carburetor in this state.
Atomized
Carburetor mixes with air in this state. To the proper stochiometric ratio of 14:1 air to fuel
Vaporized
Fuel becomes a gas in the combustion chamber on the compression stroke

15. Valve train
All components that allow for the transfer of fuel and air both fresh and burnt.

16. Valves Open and close the combustion chamber.
Seals the combustion chamber.
Allows for the transfer of fuel and air.

17. Valve seats
Inserts in the block or head that allow the valves face to rest on, and to cool and seal the combustion chamber.
Made from high carbon steel to withstand high heat and pressure.

18. Valve guide
Tube like structure in the head or block that guides the valve, and is concentric with the valve seat.

19. Valve spring
Used to keep the valve closed.

20. Valve Retainers
Used to retain the valve spring onto the valve.

21. Camshaft
Used to open and close the valves at the proper time (phasing), for a specific length of time (duration).
Driven by the crankshaft.
Gear, chain or belt driven

22. Tappets/ Lifters
Used to transfer the motion of the camshaft to the valve (L-head) or the push-rod (ohv)

23. Passageways Fuel and Air must pass into and out of the combustion chamber. Fresh fuel and air is called INTAKE Burnt fuel and air is called EXHAUST Cylinder head passageways are called PORTS MANIFOLD passageways are called RUNNERS

24. Four stroke cycle Intake Compression Power Exhaust

25. Intake stroke Piston moves down from TDC to BDC
Intake stroke Piston moves down from TDC to BDC. Cylinder creates a vacuum. Fuel and Air rush into the cylinder when the Intake Valve opens. Cylinder is now filled with the fresh fuel and air charge. Exhaust valve stays closed.

26. Compression Piston moves from BDC to TDC
Compression Piston moves from BDC to TDC. Fuel and Air is squeezed so tight that heat is generated. Fuel becomes Vaporized. Intake and Exhaust valves are closed.

27. Power Piston moves from TDC to BDC
Power Piston moves from TDC to BDC. Fuel and air is Ignited by the spark plug. Fast burning of the fuel creates a tremendous heat and pressure increase. Pressure forces the piston down with 2000 PSI of Force. Both the Intake and Exhaust valves are closed.

28. Exhaust Piston moves from BDC to TDC Exhaust valve opens,
Intake stays closed
Burnt fuel and air is forced out of the exhaust Ports and exhaust manifold Runners.

30. Four stroke cycle

31. HEAD AND BLOCK

32. CLYINDER BLOCKS

33. ALUMINUM BLOCKS

34. CYLINDER SLEEVES

35. GREY IRON

36. CYLINDER HEADS

37. Alloys

38. RECIPROCATING

39. PISTONS RINGS AND RODS

40. PRESSURE AND TEMPERATURE

41. PRESSURE AND VOLUME

42. ENERGY

43. CAMSHAFT

44. CAM PHASING

45. COMBUSTION CHAMBER

46. TURBULANCE

47. GASKETS