Engine Construction and Principles of Operation

Chapter 4

Objectives

Explain simple engine operation. List the qualities of gasoline that make it an

efficient fuel for small engines. Explain why gasoline is atomized in the small

engine. Identify the basic components of a small

engine and describe the function of each part.

How does an Engine Work?

Gasoline

Hydrocarbon fuel (mix of hydrogen and carbon)

Gas should Ignite readily, burn cleanly, resist detonation Vaporize easily w/o vapor lock Free of dirt, water, and abrasives

Octane Number

Ability to resist detonation

Low Compression = Regular

High Compression = Premium

Video 1

Video 2

Octane Number

Lead

Oxygenates

Ethanol

How does gasoline burn?

Liquid?

Vapor?

Atomizing

Containing Our Explosion

Minimizing Lost Energy

Combustion Chamber

Questions on Page 71

Cylinder Block

Keeps all parts aligned

Cast Iron

Aluminum Alloy

Cooling Fins

Function

Design

Crankshaft

Major rotating part of the engine

Forged or Cast Steel with precisely machined and ground bearings

Crankshaft

Counterweights

Crankpin or Connecting Rod Journal

Throw

Flywheel

PTO

Crankcase

Rigid and Strong

Keep Parts Aligned

Hold Oil and Keep Out Dirt

Piston

Straight line driving member of the engine

Subject to direct heat from combustion

Piston

Adequate clearance to allow for expansion

Piston rings Compression Ring:

Scraper Ring (Compression):

Oil Ring:

Piston

Ring grooves

Characteristics of a Piston

Wrist Pin (Piston Pin):

Retainers

Connecting Rod

Connects piston to crankshaft

Bearings

Bearing Cap

Intake and Exhaust Ports

Ports (Two Stroke)

Poppet Valves

Poppet Valves

Intake (Usually Larger):

Exhaust:

Poppet Valves

Valve Face

Valve Seat

Valve Stem

Poppet Valves

Valve Guide

Valve Spring

Valve Rotator

Retainer (Keeper) Pin Collar Keyhole

Valve Lifter or Tappet

Link b/w camshaft lobe and valve stem

Camshaft

Timing Gear

Lobe

Compression Release

Position?

Flywheel

Three Functions Momentum

Cooling

Ignition/Accessories

Objectives

Explain simple engine operation. List the qualities of gasoline that make it an

efficient fuel for small engines. Explain why gasoline is atomized in the small

engine. Identify the basic components of a small

engine and describe the function of each part.