1. Two-Cycle and Four-Cycle Engines
Chapter 5

2. Objectives
Describe four-stroke cycle engine operation and explain the purpose of each stroke.
Explain the concept of valve timing.
Compare the lubrication system in a four-cycle engine to the system in a two-stroke engine.
Describe two-stroke cycle engine operation and explain the principles of two-cycle operation.
List the advantages and disadvantages of two-cycle and four-cycle engines.

3. Stroke
Each time the piston moves from one end of its travel to the other (BDC to TDC and vice-versa).
Strokes are identified by the job they do.
Four-cycle engines require four strokes to complete one operating cycle.
Two stroke engines require?-

4. Four- Stroke Cycle Engine
Intake-
Compression-
Power-
Exhaust-

5. Intake
Intake Valve-
Key Functions: 1. 2. 3.

6. Compression Valves- Piston Rings-
Why does compression increase the force of combustion? 1. 2.

7. Power
Valves-
What happens?
Top dead center (TDC)-
Compression Ratio

8. Exhaust
Valves-
Scavenging-
How does the valve cool?

9. Valve Timing Figure 5-5 in book. Valve Overlap-
How are the valves timed?

10. Lubrication of a Four-Stroke
Provided by placing the correct quantity and quality of oil in the crankcase.
Pressurized System-
Splash System-
Can engine operate upside-down?

11. Lubrication of a Two-Stroke
Can be operated at extreme angles…Why?
Fuel Mixture-
Advantages-
Disadvantages-

12. Two-Stroke Design Two Basic Designs (Fig 5-8)
Cross-scavenged-(Rotary and Reed Valves)
Loop-scavenged-(3rd port design)

13. Principles of Operation
Intake into Crankcase:
Fuel Transfer:
Ignition/Power
Exhaust

14. Scavenging and Tuning
How to get the exhaust out and keep the fuel in?

15. Different Valves
Rotary Disc:
Reed:

16. List at least 10 differences in the characteristics between 4 and 2 stroke engines.

17. Objectives
Describe four-stroke cycle engine operation and explain the purpose of each stroke.
Explain the concept of valve timing.
Compare the lubrication system in a four-cycle engine to the system in a two-stroke engine.
Describe two-stroke cycle engine operation and explain the principles of two-cycle operation.
List the advantages and disadvantages of two-cycle and four-cycle engines.