| Valve
float |
A
condition which occurs at high engine speeds where valves which
open and close rapidly no longer completely close but remain partially
open all the time. When this occurs, it basically limits an engine's
speed. Exacerbated by weak valve springs. |
|
|
| Valve
guide |
A
machined hole through an engine's cylinder head where the valve
stem is inserted. Maintains proper valve alignment. Valve guides
wear after many miles and often lead to increased oil use and decreased
engine performance. Usually valve guides contains a brass or stainless
sleeve which can be replaced if worn. |
|
|
| Valve-in-head
engine |
An
engine where the valve are positioned in the cylinder head. More
commonly referred to as an overhead-valve engine. Virtually all
automobile engines contain intake and exhaust valves in their cylinder
heads. For more info see L-head engine or Flat head engine. |
|
|
| Valve
job |
An
engine repair procedure that involves removing the cylinder head(s)
(a significant job in and of itself), removing all the valves and
springs, then grinding the valves (three angles), grinding or replacing
the valve seats, grinding the tip of all the valve stems, inspecting
and replacing worn valve guides, inspecting and replacing (if necessary)
worn valve springs and valve keepers, rockers or studs. Then, the
surface of the cylinder head must be checked for warpage and most
likely resurfaced before all valves and valve components and new
valve stem seals can be reinstalled in the head and the head replaced
on the engine. |
|
|
| Valve
keeper |
Small
devices, like look like a split, cone-shaped collar with groves
on their inner edge that attach to the top of valves and secure
them in place. The valve spring must be compressed in order to install
the keepers. Then the spring is released and a retainer at the top
of the spring that has a recessed cone-shaped hole presses against
the keepers holding them tight against the valve stem and preventing
them from falling off. Two keepers are used for each valve. |
|
|
| Valve
lash |
Another
term for valve clearance. See Valve clearance (above) |
|
|
| Valve
lifter |
See Lifter or Cam follower. |
|
|
| Valve
seat |
A
machined rim in a cylinder head's combustion chamber where the valve
seats. The hole beneath each valve seat is either the intake port
or exhaust port leading to the combustion chamber. Valve seats on
modern vehicles are hardened and often removable for purposes of
replacement. The valve forms a seal against the valve seat when
inserted into the valve guide. |
|
|
| Valve
seat insert |
The
hardened metal ring that is inserted into a machined bore in the
cylinder head and forms a seat with the valve. Older vehicles that
were designed to be used with leaded gasoline did not use hardened
valve seats. When the switch-over to unleaded gasoline occurred,
it was found that the valve seats would pit under stressful conditions.
A common practice among restorers is to retrofit older cylinder
heads with hardened valve seat inserts. |
|
|
| Valves
per cylinder |
The
number of valves for each cylinder in an engine. The more valves
per cylinder the better "breathing" the engine. Most engines
have two valves per cylinder (one intake, one exhaust), but many
modern engines utilize three or four valves per cylinder. A three
valve engine would have two intake valves and one large exhaust
valves. |
|
|
| Valve
spring |
A
small coil spring fitted around a valve stem which closes (seals)
the valve after it has been opened by the camshaft. The spring also
keeps the lifter in contact with the camshaft (or pushrod) and also
forces valve keepers against the valve stem which prevents the valve
from falling into the cylinder. Worn valve springs can lead to undesirable
conditions such as 'valve float' and 'bounce' in which the valve
doesn't fully close, or bounces open during high speeds. |
|
|
| Valve
stem |
The
long, cylindrical portion of a valve which fits through the valve
guide. |
|
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| Valve
train |
All
the parts that operate and retain an engine's valves including the
camshaft, lifters, pushrods, rocker arms, drive components, springs,
retainers and the valves themselves. |
|
|
| Van |
A
tall, box-like vehicle body style where the passenger compartment
and/or cargo area extends to the rear of the vehicle. Usually have
front passenger doors, a large sliding side door and split cargo-type
doors at the rear. Vans are used by businesses to haul and deliver
large items, but vans can also be customized and outfitted with
fancy exterior graphics and plush carpeting and three and even four
rows of seats inside. Vans are typically built on a pickup truck
chassis and usually have V6 or V8 engines. Smaller vans are known
as minivans. |
|
|
| Vanity
mirror |
A
mirror which is placed in the visor on the passengers and/or drivers'
side. Sometimes contains lights for night time illumination. |
|
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| Vapor
injection |
See
Water injection. |
|
|
| Vapor
lock |
A
condition where fuel boils in the fuel system, usually the fuel
line leading from the fuel pump to the carburetor. Bubbles form
in the fuel line creating air pockets that stop or slow fuel flow
to the carburetor. In some cases, pressure from the boiling fuel
can cause the carburetor float bowl to overflow and force fuel into
the airstream leading to an excessively rich mixture that can cause
the engine to stall. Most commonly occurs on hot days during stop-and-go
traffic or sitting in a traffic jam when the motor is particularly
warm. |
|
|
| Vapor
recovery system |
See
Evaporative emission control. |
|
|
| Variable-assist
power steering |
A
power steering system that uses valves and speed sensors to vary
the amount of steering assist according to engine or road speed.
At slow speeds more steering assist is delivered and steering the
wheels is easier; necessary for parking, etc.. At higher speeds,
steering assist is reduced and more steering effort is required
to steer the car, giving the driver greater feel of the road. Also
known as Speed-sensitive power steering. |
|
|
| Variable-ratio
steering |
A
steering system where the steering ratio is not constant through
the movement of the steering. Typically the amount of tire movement
will be slow (lower ratio) when the wheels are straight, which reduces
jerky steering while cruising down the road. However, when turning
sharp corners the ratio of steering changes resulting in greater
turning at the front wheels for each turn of the steering wheel
-- which increases maneuverability |
|
|
| Variable
spring rate |
Spring
compression rates which differ over the coarse of compression.
For example, if a spring compresses an inch for each 100 lb of
weight added, it's constant is 100 lb/in. A variable rate spring
may compress 1 inch after 100 lb of weight, but may require 200
lb to compress another inch. Used widely in automotive suspension
systems to produce a comfortable ride while carrying a wide number
of passengers and still provide good handling. Also used in trucks
to provide a comfortable ride when the truck is empty, but able
to support heavy loads.
|
|
|
| Variable
venturi carburetor |
A
type of carburetion system which uses an air valve, and a system
of weights and linkages and a variable jetting system to increase
fuel to the engine based on engine demand. |
|
|
| V-belt |
A
type of drive belt used on older vehicles as a fan belt and to drive
the power steering pump, air compressor and other engine accessories.
The inner edge of the V-belt that rode on the pulley was tapered
inwards in a "V" shape (hence the name). There are several
disadvantages to this type of belt which include, tendency to slip
unless very tight, short life span, tendency to vibrate, and several
belts were required to drive the fan, alternator, air-conditioning,
power steering pump and air pump. Has been replaced with a single
serpentine belt on modern automobiles. |
|
|
| Vehicle
Identification Number (VIN) |
A
serial number assigned by the manufacturer to each vehicle which
lists the serial number, country of manufacturer, year, model, and
additional vehicle information which may include: color, axle ratio,
engine size and trim level. The VIN number must be printed on a
plate and affixed to the dash or A-pillar clearly visible from the
outside of the vehicle. Most vehicles have VIN numbers stamped on
various other places which are less obvious, and less accessible
such as on the tops or sides of the frame, floor pans, etc. to help
identify stolen cars which may have had their VIN tags removed. |
|
|
| Vehicle
Speed Sensor (VSS) |
An
electronic device usually located inside the transmission near the
output shaft which monitors vehicle speed. The computer receives
a pulsed signal and calculates vehicle speed based on a known number
of shaft revolutions, differential gearing and tire diameter. The
signal is used to control the speedometer in modern vehicles, cruise
control and is combined with other signals to determine the engine's
optimal air/fuel mixture. Dramatically changing tire size or differential
gearing will cause inaccurate speedometer readings and incorrect
air/fuel mixture ratios which may reduce power and fuel economy.
However, increasing tire size AND changing differential gearing
to match original output shaft speed will allow the vehicle to operate
close to normal. |
|
|
| Velocitized |
A
condition in which a driver who has been traveling at high speeds
for an extended period of time becomes used to higher speeds. Can
be a dangerous condition when drivers leave high speed thoroughfares
and travel local roads at high speeds. |
|
|
| Velocity |
Rate
of motion in a particular direction. Not the same as speed because
speed has only magnitude, velocity has magnitude and direction. |
|
|
| Velour |
A
type of plush fabric used on automobile seats and door panels. |
|
|
| V-engine |
An
multi-cylinder engine design where the cylinders are positioned
in a V shape when the engine is viewed from the front/rear. The
angles of the cylinders in most V engines are usually either 60,
or 90 degrees opposed. Most V engines consist of either six or eight
cylinders. The design yields a more compact engine than a straight
six or eight cylinder design. See Straight-8 or Inline engine. |
|
|
| Vented
disc brakes |
See
Ventilated disc brakes (below). |
|
|
| Ventilated
disc brakes |
Disc
brakes that use rotor which have vanes or passages between the rotor
surfaces so air can flow through for better cooling and heat dissipation.
Vented rotors cool better and resist fade better than non-vented
rotors. They are also less prone to warpage. Solid rotors which
have holes drilled in them, also called cross-drilled rotors are
also considered ventilated disc brakes. See Cross-drilled rotors.
|
|
|
| Venturi |
A
part of a carburetor mounted in the air stream which produces a
vacuum (created by air rushing through the carburetor into the motor)
which draws fuel out of the carburetor fuel bowl through the main
jets and into the passing air stream. |
|
|
| Vent
window |
A
small, usually triangle-shaped, window installed on the front or
rear doors or installed in the C-pillar. Also called vent windows
because originally they could be opened to help vent the passenger
compartment. Not found in modern vehicles. Also known as a Quarter
window, Vent wing and Wind wing. |
|
|
| Vent
wing |
Another
term for Vent window (above). So called because when opened they
would stick out in a wing-like fashion. Also called Wind wing. |
|
|
| Vibration
damper |
See
Harmonic balancer. |
|
|
| VIN |
An
acronym for Vehicle Identification Number (above). |
|
|
| Vintage |
A
term applied to old or historic vehicles. Technically one built
before 1925. |
|
|
| Viscosity |
A
fluid's resistance to flow. Caused by the internal friction between
the fluid's molecules. Used to rate motor oil thickness. Oil with
a high viscosity is thick and doesn't flow as well as a low viscosity
oil which flows easily. Nearly all manufacturers recommend multi-viscosity
oils which flow well at all normal ambient temperatures -- for optimal
engine lubrication. |
|
|
| Viscosity
index |
The
degree to which an oil's viscosity changes relative to temperature. |
|
|
| Viscous
coupler |
A
device used on many four-wheel-drive vehicles to automatically engage
the front wheels for extra traction when wheel slippage is detected.
The coupler consists of a round metal drum that contains two sets
of clutch discs each set connected to a different shaft. A fluid,
typically silicone, is present inside the coupler. When shaft speeds
change (for instance rear wheel slippage) the fluid quickly heats
up causing it's viscosity to increase and "lock" the two
plates, and therefore shafts, together engaging the front wheels.
After a time, if no differential between the plates occurs, the
fluid cools down and the front wheels are disengaged. |
|
|
| Viscous
limited-slip differential |
A
limited slip differential system which uses a viscous coupler to
limit axle slip, thereby allowing both axles to drive simultaneously
providing additional traction. |
|
|
| Visor |
A
thin, hinged flap mounted above the heads and near the top of the
windshield of the passenger and driver which can be pulled down
to shield their eyes from direct sunlight and glare. Visors usually
pivot to the side to block light coming through the side windows
as well. A vanity mirror is often placed on the upper portion of
the visor. |
|
|
| Volatility |
How
readily a fluid vaporizes. Gasoline is more volatile than diesel
fuel. |
|
|
| Volt |
A
measure of electromotive force. A single volt produces a electric
current of one amp through a resistance of one ohm. Most modern
automobiles operate on a 12 volt system. |
|
|
| Voltage
reducer |
An electric device which reduces 12 volts to 6 volts. Commonly used
by automobile restorers when converting older vehicles that were
designed for 6 volt operation to 12 volts. Although many engine
parts can easily be converted or switched to 12 volts for more efficient
operation, many power features cannot. A voltage reducer is often
used to power the radio and gauges and other accessories. |
|
|
| Voltage
regulator |
A
device in an vehicle's electrical system which limits current from
the alternator to the vehicle's circuits so they don't become overloaded.
When the battery becomes low, the voltage regulator cuts resistance
out of the alternator field current which increases current in that
circuit resulting in increased alternator output. When the battery
has become charged, resistance is returned to the field coils and
alternator output is reduced. |
|
|
| Volumetric
efficiency |
The
ratio of the actual volume of air/fuel mix that enters a cylinder
during each intake stroke to the ideal volume. Due to intake port,
head and valve designs the actual amount of air/fuel mix that enters
the cylinders during an intake stroke is less than the ideal amount
which would enter under ideal conditions. Also known as Breathing
efficiency. |
|
|
| Vulcanization |
A
process of hardening of rubber or plastic from liquid.
A
stage that occurs when making tires, usually during the tread-molding
stage. Gives the rubber a hard, yet flexible texture.
|
