Ball Bearing-A bearing in which revolving steel balls aid in overcoming friction.

Ball Cage-A metal cup, ring, or recess, holding the balls in a ball bearing.

Ball Check-A check valve in which a ball fits over the opening, in place of a regular valve.

Ball Pein-The round end of a machinist's hammer.

Ball Race-Hardened steel washers, or disks, against which the balls bear in a ball bearing.

Bearings—The parts on which a revolving surface rests, or through which it passes in contact.

Bed-The surface to which a motor is fastened by its bed plate. Bed Plate-The flat surface at the base of a motor used to attach the engine to its bed.

Bell Crank-An angular crank transmitting power, or pull, at right angles.

Bevel Gear-Cog-wheels, or gears, with sloping faces for transmitting power at an angle.

Binding Post-The post, or metal object, to which electrical wires are fastened.

Boxes-The metal casings which contain, or hold, bearings in place. Brasses Bearings of bronze or brass used in place of babbitt. Break Spark-An electrical spark produced by interrupting or breaking an electrical current.

Breaker-An object for breaking or interrupting an electrical current. Brushes Metal or carbon points used to gather or transmit electricity from the armature of a magneto to the wires.

Burr-A roughened or enlarged edge, or end, of a bolt, shaft, pipe, or other metal object.

Bushing-A cylindrical shell or casing to reduce a hole in a pipe, wheel, or other object or to enlarge the object that passes through a hole.

Butt Spark-See Kiss Spark.

By-pass-The passage through which the explosive gas passes from the base to the firing chamber of a two-cycle motor.

Cam-An irregular or variously shaped piece attached to a shaft and so designed as to transmit a varying motion.

Cam Gear-The gear used to operate a cam.

Cam Shaft-The shaft, or spindle, carrying a cam.

Calorific Power-The power actually contained in a unit of heat.

Calorific Value-The number of thermal, or heat, units contained in a certain quantity of fuel.

Cap Screw-A form of machine screw, or bolt, having a square or hexagonal head.

Carburetor-A device for so combining or mixing liquid fuel with air as to produce an explosive or combustible gas.

Castellated Nut-A nut with grooves on its top, to hold cotter pins. Catalytic Ignition-Ignition by the use of spongy platinum which becomes incandescent in contact with coal-gas or carbureted air. Centrifugal Governor—A device which regulates the speed of an engine by the centrifugal force of weights operating through springs or other devices.

Centrifugal Pump—A pump which operates by a revolving fan or wheel within a casing, and which forces water or other liquids by centrifugal force.

Check Valve-A valve so constructed that the valve lifts or opens to the pressure in one direction, but closes or seats when pressure is exerted in the opposite direction.

Choking The failure of a motor to operate properly through the surplus of oil, fuel, carbon, or restricted passages in the exhaust. Clearance The space between the top of piston at its upward limit and the interior of the top of the cylinder; space between any two objects.

Clutch-A device for holding motion or power between the motor and the mechanism to be operated and which may be thrown off or released at will.

Coil-Wire wound about an iron core used to create a greater intensity in the electrical current.

Columbia Locknut—A form of nut provided with a tapered, threaded bushing within a nut; so designed as to contract or grip the thread upon which it is screwed and thus obviate slipping or working loose.

Combustion Chamber-The chamber or space in the cylinder, or connected thereto, in which the gas is ignited or exploded. Commutator-A revolving or oscillating object connected to the wires of an armature and through the action of which the electricity is transferred by brushes to the wires. Also applied to timers.

Compression Stroke-The stroke of a piston which compresses the gas in the cylinder and at or near the limit of which the ignition and explosion take place.

Compression Cock-Same as Relief Cock.
Condenser-Numerous sheets of tin-foil placed in an induction coil

and connected to wires across the interrupter. Designed to reduce primary sparking at the contacts and to increase the current. Connecting Rod-The arm or rod connecting the piston with the crank shaft.

Constant Oil Feed-A device for constantly feeding oil while the machine is in operation. A force-feed oiler.

Contact Points-The points through which an electrical contact is made. The platinum points of the vibrator or of the electrodes on a make-and-break igniter.

Controller-A device for controlling any mechanism.

Cotter Pin-A metal pin with the two ends bent around so as to lie close together. When placed in a hole the ends are separated, thus preventing the cotter from slipping out.

Counterweight-The same as Balance Weight.
Counterbalance-The same as above.

Coupling-Any device for connecting two pipes, rods, or shafts. Crank-The offset portion of a shaft to which the connecting rod is attached and through which power is transmitted to the shaft. Crank (Starting)—The crank or handle for turning over or starting the fly-wheel of the motor.

Cranking-The operation of turning over the fly-wheel of the motor by hand to start the engine.

Crank Case-The case or recess within which the crank revolves. Crank Shaft-The shaft bearing the crank. Cross-head-The piece to which the connecting rod is attached and to which the piston rod is also fastened, and which slides in guides, thus transmitting straight linear motion to a crank by allowing the connecting rod to oscillate on a pivot through the cross-head. Current-breaker—A device for interrupting or breaking the current of electricity to produce a spark.

Cut-out-A device for allowing the exhaust to pass directly into the air without going through the muffler.

Cylinder-The portion of the motor which contains the piston and within which the explosion takes place.

Cylinder Ribs-Metal ribs, or flanges, cast upon the cylinder's external surface to radiate heat and cool the cylinder in air-cooled

motors.

Cycle—A certain period of time within which the same events occur regularly. As applied to gas engines it is practically equivalent

to "stroke" and is one-half a revolution of the fly-wheel, approx

imately.

Cyclic Phases-The phases or changes in operation during each cycle of a motor.

Dead Centre-That portion of a revolution during which the piston cannot transmit motion to the crank; the upward and downward limits of the stroke.

Deflector-The projection from the top of the piston in two-cycle motors designed to prevent the inrushing gas from passing across and mingling with, or escaping with, the exhaust and to direct its course toward the top of the cylinder.

Diaphragm-A thin plate or partition, usually flexible.

Die-A tool for cutting male screw threads on rods or pipes. Die Stock-The handles and holder for holding a die when using it. Differential Gear-A combination of gears, or wheels, so arranged that motion may be transmitted to different speeds or powers, or where the resistance is unequal the power exerted may be equalized.

Differential Cam-A cam transmitting varying motions or powers. Differential Piston-A piston composed of two pistons of different sizes and operating together to perform separate duties. Distillate Denatured alcohol or similar fuels. Distributor-A device for distributing anything. In connection with motors it is usually applied to a form of electrical device which distributes the ignition current to the various cylinders, but is also applied to devices for feeding oil or to an arrangement for leading the charges of gas to various cylinders (see Elmore motor). Dog-A mechanical appliance for transmitting certain motions. Dowell—A pin or key used to hold two pieces or parts together. Drop Tee-A pipe fitting in the form of a tee but provided with a bracket or flange for fastening to a wall or other object. Drop Ell-A pipe elbow with bracket as above.

Dynamo-A machine for generating electricity through the revolution of an armature between electro-magnets.

Dynamometer—A device for ascertaining the power necessary to operate a machine at a given speed.

Eccentric-A circular disk set on a revolving shaft with its centre out of true with that of the shaft and used to transmit reciprocating motion from rotary motion.

Eddy Current A current or irregular flow of the gas caused by square or rough corners in the passages which prevent a free flow to cr from the cylinder.

Electro-magnet-A piece of iron covered with a coil of wire. When an electrical current is passed through the coil the iron core becomes highly magnetic.

Electrodes-The two points carrying the electric current between which a spark is produced, as in a spark plug.

Exhaust-The escape of the burnt gases from the cylinder. The opening through which these gases escape.

Exhaust Valve-The valve which allows the burnt gases to escape from the cylinder.

Expansion Joint—A joint or coupling so designed as to be capable of expansion and contraction by one side sliding over the other.

Face-The smooth or flat surface of a joint or wheel.

Face Plate-A plate of metal provided with clamps by the use of which an object is held in a lathe where the surface is to be turned off or faced.

Faced Joint A joint made by having the two surfaces ground smooth and flat.

Fan-A revolving wheel or disk provided with blades or paddles for circulating air about a motor to cool it. Applied erroneously to a propeller wheel.

Feather Vibrator-A form of vibrator of very delicate construction and capable of very rapid vibration.

Flange-A projecting surface, or ridge, usually applied to parts designed to be bolted together or attached to some other object.

Flange Coupling—A joint formed by fastening two pipes or shafts together by two flanges bolted together.

Flange Union-A flange coupling when applied to pipe. Flash Point-The temperature at which a substance ignites. Flexible Coupling-A coupling composed of oscillating parts so designed as to allow the shaft to revolve even when the two parts are at an angle.

Flexible Elbow-An elbow constructed as in the above.

Flexible Joint-Same as above, but more often applied to small rods, etc.

Flexible Union—A union for connecting pipe constructed with parts which permit it to be set at varying angles.