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Daily Lesson

Daily Lesson. Small Engine Valve Types, Valve Trains, and Compression Prepared by: Brian D. Alexander Virginia Tech This presentation has not been edited by the Georgia Curriculum Office. What do a Heart and an Engine have in common?. They both contain Valves!.

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Daily Lesson

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  1. Daily Lesson Small Engine Valve Types, Valve Trains, and Compression Prepared by: Brian D. Alexander Virginia Tech This presentation has not been edited by the Georgia Curriculum Office.

  2. What do a Heart and an Engine have in common?

  3. They both contain Valves! This unit will cover valves, valve trains and the effect they have on compression.

  4. Valves and Compression • Performance Objectives: SWBAT (Students Will be Able To): 1. Describe the valve parts of a small engines 2. Explain the function of valves in an engine

  5. Valves and Compression • Enabling Objectives SWBAT: 1. Identify three types of valve systems 2. Describe the function valves serve 3. Identify the components of a poppet valve train 4. Differentiate between intake and exhaust valves

  6. Valves and Compression • Enabling Objectives (continued) SWBAT: 5. List the advantages of Over Head Valve systems 6. List and identify six different valve problems 7. List ways valves affect compression

  7. Purpose of Engine Valves • Intake valve - a valve that permits a fluid or gas to enter a chamber and seals against exit. • Exhaust valve - a valve that permits burned and unburned gases to escape, and seals against exit.

  8. Valve Systems • Poppet valves • Overhead valves (OHV) • Reed Valves

  9. Poppet Valve Assembly • Valve • Valve spring • Retainer(s)

  10. Components of a Complete Valve Train • Valve • Valve guide • Spring • Cam

  11. Overhead Valve System

  12. Overhead Valve System • Improves volumetric efficiency • Eliminates combustion chamber hot-spots • Increases fuel efficiency by as much as 25% • Improves engine service life

  13. Valves Effect Compression • It is essential that valve springs meet manufacturer specifications. • Through overheating and extensive use, valve springs can lose their elasticity and become distorted.

  14. Reed Valve System • The reed valve system can be found in 2-cycle engines • Reed valve - a flat , flexible plate that permits air or liquid to pass in one direction but seals when the flow reverses. • Picture from Ag Mec book

  15. Valve Part Names • Sec 14 p. 5 Fig 11 Briggs book

  16. Valve Operating Conditions • 1200 - 2500 degrees F • High pressure - 500 pounds/sq. inch • Open and close - 1/50 of a second (at 3000 RPM) • section 14 p. 3 fig 8 (Briggs book)

  17. Inspecting Valves & Seats • 1) Eroded, cracked, or pitted valve faces, heads, or stems • 2) Warped head • 3) Worn or improperly ground valve stems • 4) Bent valve stems • 5) Margin less than 1/64 inches • 6) Partial seating

  18. Valves Affect Compression • The correct valve seat angle is necessary for proper valve seating. • Valve seats are generally cut to a 45 degree angle, although 30 degree seat angles are used in a few engines. • Fig 16-37 p.281 yel

  19. Valves Affect Compression • The value seat width is important for effective valve system operation. • Valve seat widths range from .030 to .060 in. (1/32 - 1/16 in.) • Fig 16-36 p.281 yellow

  20. Valves Affect Compression • It is essential that valve springs meet manufacturer specifications. • Through overheating and extensive use, valve springs can lose their elasticity and become distorted. • Fig 16-30 p.279 yellow

  21. Valves Effect Compression • Valve guides align and “steer” the valves so that they can open fully and close completely. • Valve-to-guide clearance should run about .002 to .003 in.

  22. Valves Effect Compression • There are two types of valve guides • Bored in block • Pressed in block

  23. Valve Failures

  24. Engine Valves are Essential • Control intake and exhaust • Affect compression • Three major systems • Poppet, OHV and Reed

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