GLOSSARY 1149
GENERATOR: A device which produces direct current (DC) necessary to
charge the battery. OVERHEAD CAMSHAFT (OHC): An engine configuration in which the
camshaft is mounted on top of the cylinder head and operates the valve either
directly or by means of rocker arms.
HEAT RANGE: A term used to describe the ability of a spark plug to carry
away heat. Plugs with longer nosed insulators take longer to carry heat off
effectively.
HUB: The center part of a wheel or gear.
HYDROCARBON (HC): Any chemical compound made up of hydrogen
and carbon. A major pollutant formed by the engine as a by-product of
combustion.
HYDROMETER: An instrument used to measure the specific gravity of a so-
lution.
INCH POUND (inch Ibs.; sometimes in. lb. or in. Ibs.): One twelfth
.
of a foot pound.
INDUCTION: A means of transferring electrical energy in the form of a mag-
netic field. Principle used in the ignition coil to increase voltage.
INJECTOR: A device which receives metered fuel under relatively low pres-
sure and is activated to inject the fuel into the engine under relatively high
pressure at a predetermined time.
INPUT SHAFT: The shaft to which torque is applied, usually carrying the dri-
ving gear or gears.
INTAKE MANIFOLD: A casting of passages or pipes used to conduct air or
a fuel/air mixture to the cylinders.
JOURNAL: The bearing surface within which a shaft operates.
KEY: A small block usually fitted in a notch between a shaft and a hub to pre-
vent slippage of the two parts.
MANIFOLD: A casting of passages or set of pipes which connect the cylin-
ders to an inlet or outlet source.
MASTER CYLINDER: The primary fluid pressurizing device in a hydraulic
system. In automotive use, it is found in brake and hydraulic clutch systems
and is pedal activated, either directly or, in a power brake system, through the
power booster.
MODULE: Electronic control unit, amplifier or igniter of solid state or inte-
grated design which controls the current flow in the ignition primary circuit
based on input from the pick-up coil. When the module opens the primary cir-
cuit, high secondary voltage is induced in the coil.
NEEDLE BEARING: A bearing which consists of a number (usually a large
number) of long, thin rollers.
OHM: The unit used to measure the resistance of conductor-to-electrical flow.
One ohm is the amount of resistance that limits current flow to one ampere in
a circuit with one volt of pressure.
OHMMETER: An instrument used for measuring the resistance, in ohms, in
an electrical circuit.
OUTPUT SHAFT: The shaft which transmits torque from a device, such as a
transmission. OVERHEAD VALVE (OHV): An engine configuration in which all of the
valves are located in the cylinder head
and the camshaft is located in the cylin-
der block. The camshaft operates the valves via lifters and pushrods.
OXIDES OF NITROGEN (NOx): Chemical compounds of nitrogen produced
as a byproduct of combustion. They combine with hydrocarbons to produce
smog.
OXYGEN SENSOR: Used with a feedback system to sense the presence of
oxygen in the exhaust gas and signal the computer which can use the voltage
signal to determine engine operating efficiency and adjust the air/fuel ratio.
PINION: The smaller of two gears. The rear axle pinion drives the ring gear
which transmits motion to the axle shafts.
PISTON RING: An open-ended ring which fits into a groove on the outer di-
ameter of the piston. Its chief function is to form a seal between the piston and
cylinder wall. Most automotive pistons have three rings: two for compression
sealing; one for oil sealing.
PRELOAD: A predetermined load placed on a bearing during assembly or by
adjustment.
PRESS FIT: The mating of two parts under pressure, due to the inner diam-
eter of one being smaller than the outer diameter of the other, or vice versa;
an interference fit.
PRIMARY CIRCUIT: The low voltage side of the ignition system which con-
sists of the ignition switch, ballast resistor or resistance wire, bypass, coil,
electronic control unit and pick-up coil as well as the connecting wires and
harnesses.
RACE: The surface on the inner or otiter ring of a bearing on which the balls,
needles or rollers move.
REGULATOR: A device which maintains the amperage and/or voltage levels
of a circuit at predetermined values.
RELAY: A switch which automatically opens and/or closes a circuit.
RESISTANCE: The opposition to the flow of current through a circuit or elec-
trical device, and is measured in ohms. Resistance is equal to the voltage di-
vided by the amperage.
RESISTOR: A device, usually made of wire, which offers a preset amount of
resistance in an electrical circuit.
RING GEAR: The name given to a ring-shaped gear attached to a differential
case, or affixed to a flywheel or as part of a planetary gear set.
ROLLER BEARING: A bearing made up of hardened inner and outer races
between which hardened steel rollers move.
ROTOR: (1.) The disc-shaped part of a disc brake assembly, upon which the
brake pads bear; also called, brake disc. (2.) The device mounted atop the dis-
tributor shaft, which passes current to the distributor cap tower contacts.
