DEFINITION OF TERMS-CONTINUED
Overload Breaker. In an electrical circuit, a device that
another shaft or rotating part.
breaks or opens a circuit if it is overloaded by a short,
A metallic rattling sound produced in the
ground, use of too much equipment, etc.
combustion chamber resulting from air-fuel mixture
exploding rather than burning evenly.
Overrunning Clutch. A type of drive mechanism used in
a starter that transmits cranking effort but overruns freely
Pinion. The smaller of two mating or meshing gears.
when the engine tries to drive starter. Also, a special
clutch used in several mechanism that permits a rotating
A swivel-type assembly used to
member to turn freely under some conditions but not
engage with a lunette for towing trailers.
under other conditions.
Piston. In an engine, the cylindrical part that moves up
Parabolic Reflector. A reflector that sends all reflected
and down in the cylinder.
light originating at the focal point outward in parallel rays.
An enlarged area around the piston
Parallel Circuit. The electrical circuit formed when two or
more electrical devices have like terminals connected
together (positive to positive and negative to negative) so
Piston Displacement. The volume displaced by the
that each may operate independently of the other.
piston as it moves from the bottom to the top of the
cylinder in one complete stroke.
Parallelogram Steering Linkage. A steering configuration
using two short tie rods connected to steering arms and
Piston Head. A portion of the piston above the top ring.
to a long center link. The link is connected to the pitman
arm on one end and the idler arm on the other.
Piston Lands. A portion of the piston between the ring
Parking Brake. See Handbrake.
Piston Pin. The cylindrical or tubular metal pin that
Payload. The amount of weight that can be carried by a
attaches the piston to the connecting rod; also called
Positive crankcase ventilation; a system
Piston Ring. One of the rings fitted into grooves in the
designed to prevent crankcase vapors from being
piston. There are two types: compression rings and oil
discharged into the atmosphere.
The time required for the completion of one
Piston Rod. See Connecting Rod.
Pitman Arm. The arm that is a part of the steering gear;
Permanent Magnet. A piece of steel or alloy in which
it is connected by linkage to the wheel steering knuckle.
molecules are so aligned that the piece continues to
exhibit magnetism without application of external
Pivot Inclination. See Kingpin Inclination.
Planetary Gears. Set of gears that includes a central
Phase. That portion of a whole period that has elapsed
spur gear, called the sun gear, around which revolves
since the activity in question passed through zero
one or more meshing planetary gears. An internal gear,
position in a positive direction.
meshed with the planetary gears, completes the set.
Pickup Coil. A device used in electronic-type distributors
Plies. Layers of rubber-impregnated fabric that make up
that sends electrical pulses to a control unit.
the body of the tire.
Pilot. A short plug at the end of a shaft to align it with