PowerPoint ® Presentation Chapter 4 Compression System Compression Valves Valve Guides Valve Seats...

PowerPoint® PresentationPowerPoint® Presentation

Chapter 4Compression System

Compression • Valves • Valve Guides • Valve Seats • Pistons • Cylinder Bore •

Crankcase Breather System • Compression Release System • Valve

Resurfacing System • Valve Resurfacing Service Procedures

Chapter 4 — Compression SystemChapter 4 — Compression System

Competencies Describe the compression process in a small engine. List and describe compression problems. Describe important characteristics of valves. Describe valve head design and valve dynamics. Explain the function of valve guides. Explain the function of valve seats.


Competencies Explain piston design. Describe the function and types of piston rings. Explain piston ring dynamics. List and describe common piston ring materials. Describe cylinder block and bore design, and

compression release systems.


Compression Process

an adiabatic process heat is derived from the process

work applied by the piston during compression produces heat

as compression continues, temperature of the charge increases

as temperature increases, additional volatile vapor is produced


Compression Problems from inadequate or

excessive compression

compression leaks detonation Pre-ignition excessive carbon

build up


Valves one-piece valves

made from single piece of metal projection-tip welded valves

small piece of metal welded to stem two-piece-stem welded valves

head welded onto stem hardfacing

Heat treated coating added on valve face for better wear valve stem surface treatments


Valve Head Design and Valve Dynamics

45° exhaust valve face angle

30° intake valve face angle

valve spring retainer


Valve Guides

foundation of the valve system provide consistent paths for valve stems valve guide length to valve stem

diameter ratio is typically 7:1 no standard clearance specifications aluminum, brass, or sintered iron


Valve Seats

mate with valve face seals combustion

chamber removes heat

away from valves used for exhaust

valves


Piston Design

made from aluminum alloy cast and machined at the factory into a

cam ground shape designed with a taper or with a barrel-

shaped piston skirt piston windows machined channel near the piston pin


Piston Rings

seal the combustion chamber, transferring heat to cylinder wall

control oil consumption taper-faced or barrel-faced wiper ring oil ring


Piston Ring Dynamics

combination of inertia, radial pressure, and conformability ensure required seal

piston ring twist alignment of the piston ring end gaps


Piston Ring Materials

Chromium plating break-in is accomplished at any speed

above idle piston ring expander prevents improper

stressing or bending of the piston ring


Cylinder Block and Bore Design

the number and size of cooling fins on a cylinder block are determined by the thermal characteristics of the engine

compression release system


Chapter 4 Review

What types of valves are commonly used in small engines? Valves commonly used in small engines

include one-piece, projection-tip welded, or two-piece-stem welded valves.

What is the function of a piston ring? A piston ring seals the combustion chamber.

PowerPoint ® Presentation Chapter 4 Compression System Compression Valves Valve Guides Valve Seats...

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