Valve Types, Valve Trains, 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! 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 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