3
Since the fi rst edition of Small Gas Engines,
many revolutionary developments in other fi elds
have found their way into the design of small gas
engines. Some of these include higher horsepower-
to-weight ratios, fuel injection, electronic ignition,
pressure lubrication, and advanced materials.
Today’s engines last longer, use less fuel, run
quieter, are more reliable, and are much safer to
use. Because of various types of legislation, engine
manufacturers have made engines environmen-
tally safer. Mandates for safer levels of emissions
have spawned signifi cant changes to small gas
engines. The high level of technology associated
with the design and manufacture of modern en-
gines calls for closer tolerances and precise air-
fl ow, lubrication, and emission control. As engines
have become more effi cient, they have also become
more complex.
The small gas engine now serves as a labor-
saving power source for more products than ever
before.
• General applications for small gas engines
include lawn mowers, edgers, lawn tractors,
garden tillers, snow throwers, string
trimmers, brush cutters, chain saws, portable
pumps, posthole drills, and leaf blowers.
• Industrial and more specialized applications
for small gas engines include portable electric
generators, conveyor systems, cement mixers,
welding generators, lifting mechanisms,
portable winches, tampers, horizontal boring
units, trenchers, farm equipment, and golf
course maintenance equipment.
• Recreational applications for the small gas
engines include personal watercraft, minibikes,
go-carts, all-terrain vehicles (ATVs), ultralight
aircraft, outboard engines, and golf carts.
Because of the growing number of small gas
engine applications, the related career opportu-
nities are increasing. There are jobs as engineers,
Introduction
designers, lawn and garden shop owners, sales dis-
tributors, product representatives, and service tech-
nicians. For technicians, earning an Equipment &
Engine Training Council (EETC) certifi cation dem-
onstrates that the technician is profi cient at diag-
nosing and repairing outdoor power equipment.
Design Flexibility
Small Gas Engines is designed to provide stu-
dents, do-it-yourselfers, and aspiring technicians
with practical information about small gas engine
theory, construction, operation, lubrication, main-
tenance, troubleshooting, service, rebuilding, and
repair. Small engine users at all levels are fi nding
it benefi cial to have a thorough understanding of
engine fundamentals and service procedures. This
text provides detailed information about single-
and multi-cylinder, two-cycle and four-cycle gaso-
line engines.
Fonts in This Text
Throughout the chapters of this text, different
fonts are used to emphasize the meaning or use of
words, to identify important terms, and to identify
fi gure references.
Words or terms that are called out and empha-
sized always appear in italic type. For example, the
letter L may be stamped on the fastener with left-
handed threads.
Important technical terms appear in bold-
italic type. These important terms can be found
in the Technical Terms list at the beginning of the
chapter in which they appear, and most are listed
in the glossary at the back of this text. For example,
a combination wrench has a box-end wrench on
one end and an open-end wrench on the other.