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PitmanThe same as Connecting Rod.
Pitting-Wearing away or corroding of metal in the form of small

holes or indentations. Planimeter-An instrument for determining the area of indicator

diagrams. Plug-In motor parlance, the Spark Plug. Plunger-A piston. Any object working or sliding within a cavity

made to fit its surface. Plunger Pump-A pump operated by means of a plunger or piston. Port-An opening through which gas is admitted to the cylinder or

base of a motor. Pre-ignitionThe igniting or exploding of a charge of gas before the

proper time.

Primary CoilA coil for producing low-tension electricity but not

induced current. Primary Winding—The first winding on a spark coil conveying the

primary or low-tension current. Primary Wire—The wire used to convey the primary or low-tension

electrical current. Priming-Pouring or injecting liquid fuel into a cylinder to start

the motor. Placing water in a pump to start its operation. Priming Cup-A cup for priming, usually a small receptacle

attached to the cylinder and connected with the interior by a

valve or cock. Prony BrakeA device for testing the power of gasolene motors. Protractor-An instrument used for determining angles and degrees

of a circle. Puddle CarburetorA form of carburetor in which the liquid fuel

is in a pool or puddle instead of in a float chamber, and from the

surface of which the gas is drawn. Pyrometer-An instrument for measuring the temperature of exhaust


Quadrant-Any piece of metal in the shape of a quarter circle;

usually applied to the curved, notched piece which holds levers in position.

Rack-A notched, or cogged, bar operating on a cog-wheel for

transmitting rotary motion to reciprocating motion or vice versa. Rack and Pinion—The combination of a rack and a small cog-wheel or pinion.

Radiator-A device for giving off, or radiating, heat and through

which the hot water from the cylinder jacket is passed in order to

cool it. Ratchet Valve-A valve operated by a ratchet gear instead of by


Ratchet Wheel-A disk or wheel with notches or projections so formed

that it will turn in one direction but not in the other by dogs or

lugs dropping into the notches. RatioThe proportion or relation of one thing to another. Reducer-An appliance for reducing the size of an opening or of a

rod or shaft. Reducing Coupling-A coupling smaller at one end than at the other

for reducing the size of any two pipes or rods which are connected

by the coupling. Reducing Elbow-An elbow with one opening smaller than the other. Relief Cock—A cock or valve placed in the cylinder to relieve the

pressure of compression. Ribbon Vibrator-A vibrator made with a slender or thin piece of

metal to which the contact point is attached. Ring Oiler-A device in the form of a ring which is attached to the

crank shaft and serves to distribute the oil in the crank case to

the bearings and connecting rod. Ring Valve-A valve in the form of a ring or cylindrical section. Rotary Valve-A cylindrical or conical valve which rotates or re

volves on its seat instead of lifting and closing. Ruhmkorff Coil-An induction or vibrator coil.

Scavenging—The cleansing of the cylinder of burnt gases.
Secondary CoilAn induction coil.
Secondary CurrentThe induced current of an induction coil.
Secondary Wire-Heavily insulated wire for carrying the secondary

current. Self-oiling-Oiling without the aid of mechanical devices. Self-starting-Equipped with a device for starting without turning

or “cranking” the fly-wheel. Set-screw-A screw of hardened steel or other metal used to hold a

shaft or other object in place. Shaft-Any revolving rod for transmitting power or motion. Shaft Bearing—The bearing through which a shaft passes. Shaft Coupling-A coupling for fastening two ends of shafting


The escape

Shaft Hanger-A bearing for shafting attached to a frame or post

for fastening to a wall, floor, or ceiling. Shims—Thin pieces of metal placed between joints to keep the two

parts separated. Short CircuitThe passage of electricity from one point to another

without passing through the conductors provided.

of electricity through faulty insulation. Sight FeedA device by which the flow of oil or other lubricant

may be seen in exactly the amount and condition in which it is

fed to the parts to be lubricated. Silencer-A device for silencing the noise of the exhaust. Sonoscope-An instrument for determining the location of vibration

or “pound" in a motor. Spark Break—The interruption or breaking of an electrical circuit

to produce a spark. Spark Coil-A coil of either the primary or induction type which

intensifies the electrical current and produces a hotter and larger

spark. Spark Plug-A plug fitted into the cylinder and insulated therefrom

and provided with electrodes or terminals which produce the

spark. Sparking PointsThe two terminal points or electrodes from which

the spark is produced. SpindleA round rod or bar. The tapered or reduced end of a

shaft. Sprocket-A wheel provided with teeth which fit into the links of a

chain for transmitting power or motion. Sprocket ChainThe chain used on a sprocket wheel. Spur Gear—A form of cog-wheel or gear-wheel in which the teeth

are sharp or pointed. Street Elbow-A pipe elbow in which one end is male- and the other

female-threaded. Stud-A piece of projecting metal to which a nut may be attached;

a lug. Stud Bolt-A bolt threaded at each end so that it may be screwed

into a threaded hole and a nut screwed onto the projecting

portion. Stuffing Box—A box or casing through which a shaft passes and which

may be packed to prevent leakage around the shaft. Suction Stroke-The stroke of the piston which draws the charge of

gas into the cylinder or crank case.

Switch-A device by which the electrical current may be turned on

or off.

Tachometer-An instrument for measuring the number of revolutions

of a wheel or other object. Tap-A tool for cutting female threads in nuts, holes, etc. Taper Pin-A round, tapered pin used to hold two parts of machin

ery together; especially for fastening a shaft to a wheel or gear. TempletA pattern or guide for duplicating parts. TerminalThe end of a wire or electrical connection. Thermal-Relating to heat. Thermal Efficiency—The proportion of heat utilized by the engine as

indicated by the power developed as compared with the total heat

contained in the fuel used. Thermal Units—The quantity of heat required to raise one pound of

pure water from 32 degrees to 33 degrees Fahr. ThreadA spiral groove cut in a screw, or in a hole, into which a

screw is fitted. ThrottleAny device for regulating the speed of a motor by increas

ing or decreasing the amount of gas entering the combustion

chamber. ThrustThe forward tendency or push of a shaft when operating

under a load. Thrust BearingThe bearing designed to overcome the friction of

the thrust. Timer-A device for interrupting and connecting the electrical

circuit at certain intervals in order to produce a spark at the

correct time. Timing-So regulating the timer, or the valves of a motor, as to

operate at the proper time to develop the best results. Torque-A twisting or turning force. Two-cycleA form of motor in which an explosion or impulse occurs

on every upward stroke of the piston or on every complete revolution of the crank shaft.

Union-A device for connecting two pieces of pipe so that they may

be connected or disconnected without disturbing the rest of the pipe.

Valve-A device for opening or closing a passage.
Valve Box—The casing in which a valve moves.

Valve Cam-A cam which operates a valve.
Valve ChamberThe chamber within which the valve is placed.
Valve FootThe lower portion of a valve upon which push-rods or

cams operate. Valve Gear-Gears for operating the valves. Valve PortThe opening through, or beneath, a valve which is

opened or closed by the action of the valve. Valve RodA rod for operating a valve. Valve SeatThe portion of the valve box upon which the valve rests

when closed. In a rotary or slide valve the portion around the

valve against which it bears. Valve StemThe spindle or shaft that connects the valve with its

foot or handle. Vaporizer—A device for vaporizing or transforming liquid fuel to a

gaseous state by mixing it with air. Vibrator—The part of an induction coil which automatically opens

and closes the circuit of electricity through the coil. Volt-A unit of measurement of electricity denoting the force

of current. Analogous to pressure. VoltageThe amount of volts produced by a battery or generator

and which will flow from it when a circuit is completed. Voltmeter-An instrument for measuring voltage. V-motor-A form of gas engine in which the cylinders are placed at

angles with one another or in “V-shape.” V-thread-A screw thread in which the grooves are angular with

sharp or “V-shaped” angles.

Waste NutA flange or plate for fastening pipes to a floor or wall. Water-jacketThe casing outside of a cylinder and which contains

the circulating water. Web—The thin portion of a wheel connecting the hub with the rim. Whitworth Thread-A particular form of screw-thread differing from

the ordinary threads in the shape of the grooves. The standard

British thread. Wipe BreakA form of make-and-break spark in which the spark

is produced by one electrode rubbing or passing over the other. Wipe Spark-A spark produced by a wipe break. Wire Drawing—The pull or resistance caused by overcoming friction

or pressure against moving gas, or in overcoming the resistance

to a spring. Woodruff Key-A form of key which is straight on one side but

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