daily lesson small engine valve types, valve trains, and compression prepared by: brian d. alexander...
TRANSCRIPT
Daily Lesson
Small Engine
Valve Types, Valve Trains,
and Compression
Prepared by: Brian D. Alexander
Virginia TechThis presentation has not been edited by the Georgia Curriculum
Office.
What do a Heart and an Engine have in common?
They both contain Valves!
This unit will cover valves, valve trains and the effect they have on
compression.
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
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
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
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.
Valve Systems
• Poppet valves
• Overhead valves (OHV)
• Reed Valves
Poppet Valve Assembly
• Valve• Valve spring• Retainer(s)
Components of a Complete Valve Train
• Valve• Valve guide• Spring• Cam
Overhead Valve System
Overhead Valve System
• Improves volumetric efficiency
• Eliminates combustion chamber hot-spots
• Increases fuel efficiency by as much as 25%
• Improves engine service life
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.
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
Valve Part Names
• Sec 14 p. 5 Fig 11 Briggs book
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)
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
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
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
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
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.
Valves Effect Compression
• There are two types of valve guides– Bored in block– Pressed in block
Valve Failures
Engine Valves are Essential
• Control intake and exhaust
• Affect compression
• Three major systems Poppet, OHV and Reed