| Harmonic
balancer |
A
weight mounted on the front of the engine's crankshaft behind the
accessory drive belt pulley that acts as a counterbalance to reduce
or cancel out torsional twisting or torsional vibration (harmonics)
that occurs at the crankshaft. Harmonic balancers are used on nearly
all automobile engines. They are typically made of heavy cast steel
and rubber. It also cancels out vibrations (harmonics) created by
the flywheel at the opposite end of the crankshaft. A special pullers
is often needed to remove the harmonic balancer. |
|
|
| Harmonic
motion |
Periodic
motion that occurs with elastic bodies such as the vibration of a
stretched rubber band or spring. In an automobile, suspension springs
are a source of harmonic motion. Without shock absorbers to dampen
the bounce, a car would continue to oscillate up and down when encountering
a bump. |
|
|
| Harshness |
Small
undesirable bumps and jolts transmitted to the passenger compartment
from the vehicle's suspension. Manufacturers try to reduce harshness
by using progressive rate springs and rubber suspension bushings.
Generally more pronounced in automobiles with performance suspension
designs. |
|
|
| Hatchback |
A
automotive body style in which the traditional trunk lid and rear
window are replaced with a one-piece door/window combination (usually
hinged at the roof) that provides greater access to the car's rear
storage area. Often the trunk and passenger area are blended together
to increase storage capacity, particularly on smaller vehicles. On
larger vehicles, the rear seats may fold down for increased storage
capacity. |
|
|
| Hazard
lamps |
Flashing
lights which can be turned on in emergency situations or to warn other
drivers. Also known as Emergency lights. |
|
|
| HC |
See
Hydrocarbon. |
|
|
| Header(s),
Header pipes |
Shortened
for Exhaust Header. See Exhaust header. |
|
|
| Head
gasket |
A
gasket used to seal the cylinder head to an engine's block. Since
the bottom portion of the cylinder head and the upper cylinder area
form the combustion chamber, the head gasket is a critical gasket
that must withstand a lifetime of high pressure caused by explosions
that occur inside the combustion chamber. If a leak occurs, exhaust
gasses will escape reducing engine performance. The head gasket also
prevents coolant which circulates between the head and the block from
entering the cylinder (and combustion gasses and pressures from entering
the cooling system). |
|
|
| Headlamp |
Same
as headlight (below). |
|
|
| Headlight |
High-performance
light bulbs mounted on the front of vehicles to provide illumination
at night and in low-visibility conditions. Most older vehicles use
four headlights; two for high-beam (brighter), two for low-beams.
Modern vehicles use composite headlamps that are designed to complement
the aerodynamic shape of a vehicle's front end. These headlights generally
have removable/replaceable bulbs. |
|
|
| Headlight
buckets |
Metal
or composite supports behind the headlights to which the headlights
mount to. |
|
|
| Headlight
protectors |
Aftermarket
Lexan or Plexiglass covers, often tinted or colored, which can be
placed over the headlights mainly for aesthetic purposes.
Also,
wire mesh screens which cover the headlights to protect off-road
vehicle headlights from damage from tree limbs and stones.
|
|
|
| Headliner |
Vinyl
or cloth material that covers the inside of a vehicle's roof, usually
complements the rest of the vehicle's interior color. Headliners can
be suspended by metal bows that run laterally along the roof, or can
be combination of cloth and foam or vinyl adhered to a specially formed
cardboard or foam panel bolted or screwed to the roof. Foam headliners
help reduce interior noise but often sag after many years exposure
to heat. |
|
|
| Headrest |
An
extension on the back of the seat, designed in part for comfort but
mainly to reduce head and neck injuries (whiplash) in the event of
a front or rear collision. Headrests are typically adjustable but
may also be permanently fixed or an integral part of the seatback. |
|
|
| Head
restraint |
Another
term for headrest (above).
|
|
|
| Heads-up
display (HUD) |
A
type of display that projects a lighted image of a vehicle's instrument
readout onto the windshield. The advantage is a driver can view necessary
vehicle information without removing his/her eyes from the road, thereby
improving safety. Similar systems are also used in fighter planes.
|
|
|
| Heat-control
valve |
A
butterfly valve located in the exhaust manifold that is thermostatically
controlled. When the engine is cold the valve is closed and some exhaust
gasses are diverted through the intake manifold to help preheat the
air/fuel mix before it enters the cylinders. Also called Heat-Riser
Valve. |
|
|
| Heated
intake |
An
anti-pollution scheme where the air cleaner draws heated air from
around the exhaust manifold to help fuel in a cold engine vaporize,
which reduces hydrocarbon output. Generally such systems consist of
a vacuum controlled butterfly valve in the engine's air cleaner snorkel.
When the engine is cold, the valve closes and warm air is drawn through
a passage which leads to a heat-stove around the exhaust manifold.
Fuel is sprayed into the warm air as it passes through the carburetor.
The warm air/fuel mix more easily vaporizes in the vacuum produced
in the engine's intake making combustion more efficient. Once the
engine opens up, the valve opens allowing cooler air to be drawn from
the atmosphere. |
|
|
| Heated
mirror |
A
mirror which contains a heating element to melt ice and snow. |
|
|
| Heated
seats |
Seats
which contain heating coils to warm seats. Usually found on leather
seats where the leather can remain cold for a long time in the winter. |
|
|
| Heated
windshield |
A
windshield which contains a silver-oxide (or other element) film that
becomes warm when current is passed through. Effective at quickly
melting ice and snow. |
|
|
| Heat
exchanger |
Devices
used to transfer heat between fluids and to the air. The vehicle
radiator, air-conditioning condenser, transmission cooler, oil cooler
and heater core are all examples of automotive heat exchangers.
Also,
Automobiles with air-cooled engines use a heat exchanger that fits
over the exhaust manifolds to heat the passenger compartment. Used
in the original VW Beetles. Heat exchangers do not typically work
well and early Beetles were notorious for their poor heat.
|
|
|
| Heat
range |
Refers
to the relative temperature of the core nose of a spark plug (the
end that protrudes into the combustion chamber). Spark plugs are
available in different temperature ranges for most engines, defined
as "Hot" and "Cold" to accommodate different
operating conditions. The terms hot and cold actually refer to the
thermal characteristics of the plug -- it's ability to dissipate
heat from its firing end into the engine's cooling system.
A
cold plug has a shorter nose and uses electrode and insulating materials
that rapidly transfer heat away from its firing end to the cylinder
head and thus the cooling system. Cold plugs are used to avoid high
core nose temperatures, particularly in situations where combustion
chamber or cylinder head temperatures and pressures are relatively
high, such as in racing (where high compression, high speed engines
are used) and towing and other demanding situations. So the cold
plug tip operates cooler because it conducts heat away from the
combustion chamber faster.
A hot spark plug has a longer core nose on it's firing end and therefore
transfers heat to the engine's cooling system more slowly. The tip
of "Hot" plugs operates at a higher temperature and are
used primarily in relatively cool combustion chamber conditions
where the hotter core nose of a hot plug can burn off deposits to
avoid fouling, particularly in engines where oil fouling is a problem.
The
temperature range of a plug does not affect power output. The correct
heat range is found when a plug prevents fouling but does not get
hot enough to contribute to the preignition or detonation.
|
|
|
| Heat
shield |
A
plate, typically made of aluminum or metal that prevents heat from
radiating. Used on most vehicles around exhaust manifolds to prevent
heat from melting nearby wires. Also used on most exhaust systems,
particularly above and below catalytic converters to prevent high
temperatures from entering the passenger compartment or starting fires
when parked over tall grass. |
|
|
| Heat
Stove |
A
metal shield surrounding a portion of the intake manifold where warm
air can be drawn. Most engines use heat from a heat stove around an
exhaust manifold to preheat the air/fuel mix in a cold engine in order
to reduce hydrocarbon output. Also see Heated intake (above). |
|
|
| Heat
treatment |
Controlled
heating and cooling of metals to manipulate their hardness and elasticity
properties. Used on engine and suspension parts. |
|
|
| Heel-and-toe
|
A
driving technique where the driver puts his right heel on the throttle
and toes (of the same foot) on the brake pedal. Using this technique,
the driver can simultaneously control throttle and braking. Useful
for quick downshifts. Reduces stress on the clutch and transmission. |
|
|
| Heim
joint |
A
type of precision joint used in racing and high-performance applications
that replaces traditional ball and stud type steering joints and rubber
bushings used on throttle linkages. Consists of a flat spherical movable
ball that is pressed into the end of a rod. The ball has a hole drilled
in it so it can be mounted to suspension or other movable parts. Very
precise type of movable joint. |
|
|
| Helical
gear |
A
type of gear where the teeth are cut at an angle or spiral. This increases
gear tooth surface area and yields quieter operation. |
|
|
| Helper
spring |
An
aftermarket arched leaf spring which can be installed on sagging leaf
spring to increase it's arch and raise the height of the vehicle. |
|
|
| Hemi |
An
endeared term applied to some Chrysler vehicles that used engines
with a hemispherical combustion chamber design. See Hemispherical
combustion chamber design (below). |
|
|
| Hemispherical
combustion chamber |
A
highly efficient combustion chamber design that is dome-shaped. The
dome shape allows the use of intake and exhaust valves as well as
straight intake and exhaust ports. The result is a combustion chamber
that has a small surface-area-to-volume ratio which minimizes heat
loss and charge cooling which produces high hydrocarbon emissions.
Also called Hemi. |
|
|
| Hesitation |
Sudden
and intermittent loss of power or engine response during acceleration.
Can be caused by an ignition "miss" or very lean air/fuel
mix. Particularly problematic in carbureted vehicles when the engine
is cold. |
|
|
| High-back
seat |
A
tall car seat where the head rest is built into the seat. |
|
|
| High
beam |
The
secondary (brighter) filament in a headlight in a car with a two headlight
system. In vehicles with four headlights, it's the pair of brighter
headlights. High beam lights are not only brighter but they are aimed
higher and further apart (to project further down the road) than low
beam lights. Therefore they provide greater illumination both straight
ahead and on the sides of the road. |
|
|
| High
gear |
A
transmission's "top" gear, normally used for highway cruising.
In a four speed transmission it's the 4th gear (5th gear in a 5 speed).
In an automatic transmission it's the overdrive position on the gear
selector. |
|
|
| High
tension leads |
Another
term for ignition wires, or spark plug wires. The large wire that
carries current from the coil to the distributor cap and from the
distributor cap to each of the engine's spark plugs. |
|
|
| High-test
fuel |
Another
term for high-octane rated gasoline. |
|
|
| Hog
rings |
C-shaped
wire pieces with sharp ends that can be squeezed together with a hog
ring pliers to fasten upholstery to seats. Traditionally used on farms
to fasten identification tags to a hog's ear. |
|
|
| Homologated |
A
production car that is certified to be used in certain racing classes,
or vise versa, race cars which are produced in enough volume to qualify
for a race class. Comes from the British term 'Homologated' which
is applied to race cars that are built in road-going form in enough
quantity to qualify it as a "production" car, as is required
by certain racing classifications. |
|
|
| Hone |
A
tool with spring-loaded abrasive stones that is rotated inside a machined
bore to correct irregularities such as ridges and rust pits. A common
example is a small brake cylinder hone which can be hooked onto the
end of a common hand drill and rotated inside a brake cylinder bore
to remove rust and pits that frequently form on the surface of the
bore. Engine builders use larger hones to remove ridges, burrs and
scratches on the inside of a piston's cylinder. The hone also leaves
behind small micro-scratches (called cross hatches) which help trap
oil that in turn helps the rings seal better to the cylinder wall
producing good compression. |
|
|
| Hood |
The
hinged body panel on the front of the automobile that covers the engine
(known as the "bonnet" in Britain). In British automotive
terminology, the hood is the folding top of a convertible. |
|
|
| Hood
hinges/springs |
A
device used on hoods and trunks to allow it to swing open and close.
Older vehicles used a complicated hinge/spring contraption that helped
raise the hood and keep it open. Modern vehicles use a simpler hinge
design and gas compression struts to raise and keep the hood open,
or only a hinge and a prop rod. Also see Gas struts. |
|
|
| Hood
latch |
A system using a latch and cable to secure and remotely open a hood.
All vehicles have a secondary safety latch which prevents the hood
from flying open if the primary latch were to come unlatched while
driving, or the hood wasn't properly latched. |
|
|
| Hood
ornament |
A
decorative object, usually made of chromed steel placed on or near
the front of the hood. |
|
|
| Hood
pins/locks |
Metal
pegs frequently used on race cars and street rods that protrude the
front of the hood to prevent the hood from opening while driving.
More secure than a hood latch. Locks can also be installed on the
pins to prevent unwanted entry into the engine compartment. |
|
|
| Hood
scoop |
A
duct mounted to an engine's carburetor that protrudes through a
hole in the hood which serves to channel more and cooler air into
an engine's intake than it would otherwise draw in. Used widely
on race cars and high-performance vehicles as an inexpensive method
of "forcing" more air into an engine at high speeds. A
"shaker" hood scoop attaches to the motor and sticks through
a large hole in the hood. When the engine idles, the scoop shakes.
Also see Forced induction, Turbocharger, Supercharger and Cowl induction.
|
|
|
| Hood
struts |
See
Struts. |
|
|
| Hooke
joint |
Similar
to Cardan joint. See Cardan joint. |
|
|
| Hop
up |
A
colloquial term used to describe modifying a production vehicle to
increase it's acceleration, braking and/or handling. |
|
|
| Horizontally
opposed engine |
See
Flat engine. |
|
|
| Horn |
An
electromechanical device consisting of a switch, wiring and a buzzer
which produces noise when activated. Used to warn or communicate to
other drivers. Large trucks often use air horns which are louder. |
|
|
| Horn
ring |
A
type of horn button used on the steering wheels of many classic cars
which had a circular, or semicircular metal ring that made activating
the horn easier. |
|
|
| Horsepower
(HP) |
A
measurement of power that most engines in the United States are measured
by. One horsepower is equal to 550 ft-LB/sec, or 33,000 ft-LB/min.
Engine horsepower rating is determined by tests conducted on an engine
dynamometer. Vehicle horsepower (power at the wheels) is determined
thorough tests conducted on a chassis dynamometer. |
|
|
| Horsepower
curve |
See
Torque curve |
|
|
| Hotchkiss
drive |
A
type of rear axle and suspension design used on the rear end of most
pickups and sport utility vehicles where a one-piece axle housing
is located by semi-eliptical leaf springs. The springs connect to
the vehicle frame at their ends and the axle is hung from the springs.
The advantage of such a system is simplicity of construction and ruggedness.
There is also good transmission of driving forces (cornering, braking,
bumps) from the axle to the chassis. |
|
|
| Hot
plug |
See
Heat range. |
|
|
| Hot
spot |
A
term racers and engineers used to describe areas in an engine's combustion
chamber that tend to build up excessive heat -- usually near the valves
or spark plug area. Hot spots can lead to preignition (detonation).
|
|
|
| Hot
wire |
Slang
that describes connecting wires to start a car (without the key) by
circumventing the ignition switch. |
|
|
| Hour
meter/gauge |
An
instrument which indicates the amount of time (in hours) that the
engine has been in operation. More accurate than miles, and particularly
useful on off-road vehicles or machinery which may see a particularly
high amount of idle time or don't have speedometers. |
|
|
| Hub |
The
center of a wheel that goes over the lugs and contacts the vehicle
wheel mount.
Also
the part of a floating axle setup that mounts to the axle to which
the wheel bolts to.
|
|
|
| Hubcap |
A
stylish metal or plastic cover that fits over a wheel and protects
it's lugs and bearings. Technically speaking a hubcap fits over the
center part of the wheel only. A wheel cover, used more commonly on
modern vehicles, covers the entire wheel. |
|
|
| HVAC |
An
abbreviation for Heating, Ventilation, and Air-conditioning system.
|
|
|
| Hydraulic |
Having
to do with fluids which are incompressible such as water or oil. Automobiles
use hydraulic principles in automatic transmissions, power steering
and brake systems. The incompressible fluid can be used in to transmit
power through passages and hydraulic lines from one location to another.
In a hydraulic brake system, power is transmitted from the master
brake cylinder to wheel cylinders that apply the brakes at each wheel. |
|
|
| Hydraulic
assist |
Hydraulic
pressured produced usually by an engine-driven pump that can be used
to reduce the effort needed to control certain functions, most notably
steering. Used also to decrease braking effort in diesel engine equipped
vehicles where manifold vacuum is not sufficient for a typical vacuum-opperated
brake booster. |
|
|
| Hydraulic
fluid |
The
working fluid used in hydraulic systems to transmit force from one
location/device to another. Usually an oil specially blended to
reduce foaming and non hygroscoic (does not easily absorb moisture).
|
|
|
| Hydraulic
pump |
A
device that pressurizes hydraulic fluid. In an automobile a hydraulic
pump (power steering pump) is used to create pressure for the vehicle's
power steering system. The engine's oil pump is also a hydraulic pump. |
|
|
| Hydraulic
valve lifter |
A
lifter that uses hydraulic pressure from the engines oil system to
maintain contact with the valve or pushrod at all times. Hydraulic
lifters are much quieter and require no adjustment for wear because
any wear is automatically compensated for by the lifter. |
|
|
| Hydrocarbon
(HC) |
A
compound made up of hydrogen and carbon that is produced when gasoline
is burned in an automobile. Leads to smog. Also see Emission controls
and Smog. |
|
|
| Hydrolock |
A
potentially damaging condition caused when excessive water enters
an engine's cylinders causing the engine to stop running. Can occur
from crossing deep streams if water gets sucked into the air intake.
Water is not compressible like air and therefore stops the pistons,
nearly instantly. Usually leads to engine damage (bent connecting
rods and valves), but if the engine was shut down in time and no damage
occurs, water can be removed by removing the spark plugs and turning
the engine over. Then restarted. |
|
|
| Hydroplaning |
A
condition where a tire "rides" on the surface of water rather
than maintaining contact and gripping the road surface. A tire's tread
is designed to channel water away from it's contact patch. When too
much water exists for the tire to pump away from it's leading edge
the water acts as a wedge and lifts the tire resulting in a hydroplaning
condition. The net result is a momentary loss of traction. In severe
conditions, a loss of steering can occur which leads to many accidents
per year. Worn out tread, high speeds, and excessive water depth increases
a tire's potential to hydroplane. Also known as Aquaplaning. |
|
|
| Hydropneumatic
suspension |
A
rear suspension system used of some vehicles (Citroen - Mercedes Benz)
that uses a dual-chamber cartridge separated by a rubber bladder with
gas on one side and hydraulic oil on the other side to suspend the
vehicle. |
|
|
| Hyperaspirated |
An
engine equipped with a turbocharger or blower which forces air into
it's intake. An engine that draws air into it's cylinders under normal
circumstances is known as Normally Aspirated. Forced air into the
cylinders is called hyperaspirated. |
|
|
| Hypoid
gear |
A
type of gear system commonly used in the drive axles of rear wheel
drive vehicles where the pinion is located below the centerline of
the ring gear. Such a system lowers the driveshaft height and allows
engineers to design vehicles with lower floors and therefore increased
passenger compartment room. |
