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Chapter 5

Chapter 5. Two & Four Cycle Engines page 77 Questions on pg 90. Small Engine Identification. # of strokes for a cycle 2 4 rotary. Four Stroke Cycle Engine. Intake Compression Power Exhaust. Intake. Intake open Exhaust closed Piston moves downward Vacuum. Compression.

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Chapter 5

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  1. Chapter 5 Two & Four Cycle Engines page 77 Questions on pg 90

  2. Small Engine Identification • # of strokes for a cycle • 2 • 4 • rotary

  3. Four Stroke Cycle Engine • Intake • Compression • Power • Exhaust

  4. Intake • Intake open • Exhaust closed • Piston moves downward • Vacuum

  5. Compression • Both valves closed • Piston moves up • Compression 9:1

  6. Power • Both valves closed • Spark • Ignites air/fuel mixture • 14.7:1 • Piston forced down

  7. Exhaust • Exhaust valve opens • Intake valve closed • Piston moves up • Pushes exhaust out

  8. Valve Timing • Valves must open and close at correct time • Align marks • Backfire • Lack power

  9. Lubrication • Splash • Pressure • Hybrid

  10. Two Stroke Cycle Engine • See: • http://science.howstuffworks.com/two-stroke2.htm

  11. Variation in Design • Cross-scavenged • Contoured piston head • Deflect air upward • Reed valves/rotary valves • Loop-scavenged • Flat or domed piston • Intake offset for exhaust

  12. Principles of Operation • Location of parts essential

  13. Intake into Crankcase • Piston moves up • Causes vacuum • Reed/rotary valve opens

  14. Fuel Transfer • Piston moves down • Pressurizes crankcase • Transfer port • Intake port uncovered • Air/fuel rush in

  15. Ignition Power • Air/fuel compressed • 8:1 compression • TDC-spark • BTDC-advance (warm)

  16. Exhaust • Exhaust port exposed • Intake pressure in • forces exhaust out

  17. Scavenging & Tuning • Proper design • Full scavenging

  18. Rotary Disc Valve Engine • Intake in crankcase • No reed valve • better fuel transfer

  19. Reed Valve Engine • Intake directly into crankcase • Flexible spring steel • Reed stop • Limits valve opening • Reed opened by atmospheric pressure • Closed seals crankcase

  20. 4 Cycle VS 2 Cycle • 4 cycle • More power • More fuel efficient • No-premix • 2 cycle • Simple design • Smaller lighter • Runs at any angle • High speeds

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