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Figure 2-14.—T-head engine. | Up
Construction Mechanic Basic Volume 01 - Construction methods and practices | Next
Figure 2-18.—Horsepower. |
Figure 2-16.—Double overhead camshaft configuration.
Q8.
In a horizontal-opposed engine, the cylinders
are arranged at what number of degrees from
each other?
Q9. What type of head design has the valves
arranged directly over the cylinder?
Q10. What type of head design has exhaust valves
located in the engine block?
ENGINE MEASUREMENTS AND
PERFORMANCE
LEARNING OBJECTIVE: Identify terms,
engine measurements, and performance
standards of an internal combustion engine.
As a Construction Mechanic, you must know the
various ways that engines and engine performance are
measured. An engine may be measured in terms of
cylinder diameter, piston stroke, and number of
cylinders. It may be measured, performance wise, by
the torque and horsepower it develops and by
efficiency.
DEFINITIONS
WORK is the movement of a body against an
opposing force. In the mechanical sense of the term,
this is done when resistance is overcome by a force
acting through a measured distance. Work is measured
in units of foot-pounds. One foot-pound of work is
equivalent to lifting a l-pound weight a distance of 1
foot (fig. 2-17). Work is always the force exerted over a
distance. When there is no movement of an object, there
is no work, regardless of how much force is exerted
ENERGY is the ability to do work. Energy takes
many forms, such as heat, light, sound, stored energy
(potential), or as an object in motion (kinetic energy).
Energy performs work by changing from one form to
another. Take the operation of an automobile for
example; it does the following:
When a car is sitting still and not running, it has
potential energy stored in the gasoline.
When a car is set in motion, the gasoline is
burned, changing its potential energy into heat
energy. The engine then transforms the heat
energy into kinetic energy by forcing the car into
motion.
The action of stopping the car is accomplished
by brakes. By the action of friction, the brakes
transform kinetic energy back to heat energy.
When all the kinetic energy is transformed into
heat energy, the car stops.
POWER is the rate at which work is done. It takes
more power to work rapidly than to work slowly.
Engines are rated by the amount of work they can do per
minute. An engine that does more work per minute than
another is more powerful.
The work capacity of an engine is measured in
horsepower (hp). Through testing, it was determined
that an average horse can lift a 200-pound weight to a
height of 165 feet in 1 minute. The equivalent of one
horsepower can be reached by multiplying 165 feet by
200 pounds (work formula) for a total of 33,000 foot-
Figure 2-17.—One foot-pound of work.
2-13
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