The Jargon Page

Most branches of technology have a certain number of jargon terms associated with them.  New terms may appear over time as the technology evolves.  Old terms fall into disuse.  If you are just starting to explore the early history of internal combustion engines, this list of jargon terms and definitions should help you become familiar with some of the fascinating and prominent features of early engines.  Note that a number of these features, refined and repackaged, are still in use on modern engines.

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Air Injection Engine  Air Injection Engine - A engine that uses high pressure air to inject liquid fuel directly into the cylinder near the peak of the compression stroke.  The fuel ignites as it encounters the hot, compressed air in the cylinder.  Air pressure as high as 1000 psi is often necessary to operate this type of fuel injection system.  A number of early diesel engines used this system of fuel injection before solid injection technology was developed to directly pressurize, inject, and atomize liquid fuel.
Air Start Air Starting - A method of starting an engine by injecting compressed air into the cylinder(s) to initially roll the engine.  The timing and flow of compressed air may be controlled manually or mechanically.  Air starting is particularly useful for engines that are too large to be easily or safely started by hand.
Alligator Linkage  Alligator Linkage - A cam and follower arrangement where the cam pivots at one end and the lobe near the opposite end of the cam contacts and moves a follower.
Atmospheric Engine Atmospheric Engine - An engine that does not compress the fuel-air mixture prior to ignition.  The initiation of combustion occurs at, or near, atmospheric pressure.  Also known as a non-compressing engine.
Atmospheric Intake Atmospheric Intake - An intake valve operated by the difference between atmospheric pressure and cylinder pressure.  The intake valve stem and spring are shown above the power operated exhaust valve in this photo.  Also known as an automatic intake.
Bar Over Bar Over - To manually turn an engine over using a lever.  In some designs the lever is inserted directly into pockets in the face of the flywheel rim.  In other designs, as shown in the photo, the lever operates a ratchet mechanism that engages pockets in the face of the flywheel rim.
Camstopper Camstopper - A means of hit and miss engine speed governing where the camshaft or side shaft stops rotation, thus stopping valve action and fuel induction to prevent the engine from producing power cycles.  Also see declutching sideshaft.
Charging Cylinder Charging Cylinder - A cylinder and piston, separate from the engine's power cylinder, used to force air, or fuel and air mixture, into the engine's power cylinder.
Chimney Chimney - The device that surrounds and heats a hot tube.  A chimney typically has a burner at its base.  The burner, shown entering the chimney from the right in this photo, creates a hot spot on the tube.  Some designs of chimney are adjustable so that the location of the hot spot on the tube may be changed to adjust ignition timing.  Placing the hot spot further from the cylinder retards ignition.  Placing the hot spot closer to the cylinder advances ignition.  Also known as a furnace.
Compressor Engine Compressor Engine - An engine that includes a means for compressing gas (often air) as an integral part of its overall structure.  Some compressor engines contain both a power piston and a compressor piston operating in tandem in the same cylinder.
Compression Release Compression Release - A device for allowing a portion of the compressed air and fuel mixture in the engine's cylinder to escape, lowering compression and allowing the engine to be rolled more easily for starting.  Compression releases may hold an intake or exhaust valve open.  Another type of release consists of a hand-operated valve on the cylinder, as shown in the photo.  Depending upon their design, compression releases are automatically or manually deactivated once the engine is running.
Convertible Engine Convertible Engine - An engine that can be run either as a steam engine or as an internal combustion engine.  Some half breed engines include convertible operation.
Counterbalanced Crankshaft  Counterbalanced Crankshaft - A crankshaft with balance weights installed opposite the crank pin.  The balance weights help to offset the weight of the piston and connecting rod resulting in smoother operation.
Crank Fender Crank Fender - A shield placed around the crankshaft to contain oil droplets thrown by the moving crankshaft and connecting rod.
Crosshead Cross Head - A sliding bearing that supports the piston rod and carries the wrist pin attachment point for the connecting rod.  A cross head allows the piston rod to move in a straight line and reduces side loads on the piston.  In some applications it allows the cylinder end and piston rod to be sealed so that the area behind the piston may be used for compressing gas or may be used for combustion in a double-acting cylinder.
Crowned Flywheel  Crowned Flywheel - A flywheel with the diameter slightly larger in the center of the rim than at the edges of the rim.  The raised center of the flywheel helps to stabilize and position a flat belt running on the face of the flywheel rim.
Declutching Sideshaft Declutching Side Shaft - A means of Hit and Miss engine speed governing where the side shaft stops rotation to prevent the engine from producing power cycles.  Also see camstopper.
Disc Crank Disc Crank - A form of crank assembly where the crank pin is mounted between a pair of discs. The discs are attached to the "half" sections of the crank shaft.
Electric Lighting Electric Lighting Engine - An engine with exceptionally heavy flywheels, sometimes lead-filled, designed to provide minimal speed variation between power cycles when driving a generator.  Minimizing speed variations reduces flickering of lights powered by the generator.
English Style Exhaust Valve Spring  English Style Exhaust Valve Spring - A spring in tension that holds the exhaust valve closed.  The spring is  located away from the hot portions of the engine to avoid thermal damage to the spring.
English Flywheel English Style Flywheel -  A flywheel cast with curved spokes.  Many engines built in England featured this design.  The curved spoke design was believed to result in a higher success rate in producing flywheel castings.
Face Cam Face Cam - A type of cam that has the lobe machined on the front face of a disk.  The follower rides the face of the disk to engage the cam lobe.
Flyball Governor Flyball Governor -  A speed regulation device that uses a set of flyweights to actuate linkages that control engine speed.  The governor may regulate speed by modulating the intake of fuel and/or air or it may regulate speed by controlling combustion hit and miss.
Flyweights Flyweights - A set of pivoted masses mounted to a governor shaft that move in proportion to the speed of the shaft.  The flyweights swing away from the shaft as speed increases.  They swing toward the shaft as speed decreases.
Flywheel Flywheel - An energy storage device that provides power for induction, for compression, for exhaust, and for operating the engine's load between power cycles.  The engine accelerates and "charges" the flywheel during the power cycle.  The flywheel decelerates and "discharges" as it provides power during the other cycles. 
Gearless Gearless Engine - An engine that mechanically operates the intake and exhaust valves, ignition, and fuel supply without the use of gear-driven mechanisms.
Half Breed Engine Half Breed Engine - A steam engine that  was converted to internal combustion operation by replacing the cylinder and other parts while retaining the main frame, flywheels and the bulk of the engine.  Manufacturers often produced kits of parts for the conversion.
High Tension Ignition High Tension Ignition - An ignition system that uses high voltage to create a spark across a fixed air gap in the cylinder.
Hit and Miss Governing Hit and Miss Governing (Also Hit or Miss Governing) - A form of engine speed regulation where power cycles are permitted ("hits") or prohibited ("misses") to maintain speed within the governed range.  The energy released in each power cycle is relatively constant regardless of engine load. When lightly loaded, the engine may miss many power cycles before hitting to recover speed.  The small pendulum governor in the photo interrupts the introduction of fuel to this engine to regulate speed.
Hopper Cooling Hopper Cooling -  A form of evaporative cooling system where the engine cylinder is surrounded by an open-topped chamber that is filled with water.  As water evaporates it escapes into the atmosphere carrying away heat.  The operator of the engine periodically replenishes the supply of water.
Hot Bulb  Hot Bulb - A form of vaporizer using a lightbulb-shaped chamber attached to the cylinder.  The hot bulb is heated by an external burner for starting and for low load operation.  At higher loads the combustion occuring within the hot bulb maintains its temperature. 
Hot Start Engine  Hot Start Engine - An engine that requires an external heat source, such as a burner or torch, to initially raise the temperature of components, usually the engine's vaporizer, to a point sufficient for starting.
Hot Tube Hot Tube - A form of ignition system that uses an externally heated tube that opens into the combustion chamber.  The tube is sealed on the opposite end.  Hot tubes are typically mounted in a chimney heated by a burner.  In this photo the upper portion of the chimney is removed to show the hot tube.  The burner enters this chimney from the right in the photo.  The burner creates a hot spot on the tube.  Fuel and air mixture enters the tube as the piston nears the top of the compression stroke, .  Combustion begins in the tube at the hot spot and travels out of the tube and into the cylinder. 
Illuminating Gas Illuminating Gas - A flammable gas produced from coal.  Illuminating gas contains hydrogen as well as carbon monoxide.  It was originally produced as fuel for gas lamps but also found use as fuel for internal combustion engines.  Also known as town gas or coal gas.
Low Tension Ignition Low Tension Ignition - An ignition system that uses low voltage, often supplied by a battery, to create a spark in the combustion chamber.  Low tension ignition often involves some form of make and break mechanism.
Lubricator  Lubricator - A device for applying a regulated amount of oil to engine bearings and other moving parts.  Lubricators are made in many different designs, some providing gravity feed, others providing mechanical feed.
Magneto  Magneto - An electrical generator that uses permanant magnets to provide a magnetic field.  Electricity is  produced when a coil of wire moves in the magnetic field of stationary magnets or when magnets move past a stationary coil of wire.  Some types of magneto can produce high voltages for high tension ignition systems.
Main Frame Main Frame - The casting or weldment that forms the base of the engine.  The cylinder, crankshaft and other engine parts are mounted on the main frame.  The main frame may be fastened to a floor or other structure to secure the engine.
Make and Break Igniter Make and Break Igniter - A form of low tension ignition system where a pair of contacts, at least one of which is movable, are placed in the engine's cylinder.  When the contacts are closed, electric current flows through the contacts.  When opened, a spark occurs and ignites the fuel and air mixture in the cylinder.
Match Starter Match Starter - A form of engine starting device that uses a "kitchen" match to provide first ignition.  A match is inserted into the starter and the starter is closed to prevent loss of compression.  The match is exposed to the fuel and air mixture in the cylinder.  The engine is turned back on compression and the starter is then operated to strike the match.  The match lights and ignites the compressed fuel and air mixture in the cylinder producing the first power cycle and rolling the engine.
Mixer Mixer - A device for metering fuel into air to produce a fuel and air mixture for induction into an engine's cylinder(s).
Oil Engine Oil Engine - A type of engine designed to use kerosene or heavier oil as fuel.  Oil engines use compression ignition but do not have a compression ratio high enough to directly ignite the fuel.  Instead, they generally use some form of vaporizer to preheat and prepare the fuel for ignition. 
Open Flame Open Flame Ignition - A form of ignition system that introduces an externally-produced flame into the fuel and air mixture in the cylinder.  The flame may be drawn into the cylinder from an external burner or it may be carried into the cylinder by a slide valve arrangement.
Pendulum Governor Pendulum Governor - A speed regulation device that uses a swinging pendulum set in motion by the engine to actuate linkages that control engine speed.  This type of governor typically controls combustion hit and miss.
Piano Base Piano Base (also Grand Piano Base) - A feature of early Crossley engines where the main frame beneath the crankshaft was much wider than the main frame beneath the cylinder.  The rounded form of the main frame bears a resemblance to a piano.
Pony Motor Pony Motor - A small engine used to start a large engine.  Although it adds mechanical complexity, the pony motor eliminates the need for a bulky air starting system or a large electric starter and heavy batteries.  The pony motor itself may be hand started or may be started with a small electric motor and modest-sized battery.
Ported Cylinder Ported Cylinder - An arrangement for providing an exhaust path from a cylinder via a hole in the cylinder wall.  In some designs, the ported exhaust provides the initial exhaust path with the piston near the bottom of the power stroke.  An exhaust valve then provides the subsequent exhaust path as the piston moves through the exhaust stroke.  The port reduces the heat load on the exhaust valve, extending its service life.
Power Operated Valves Power Operated Valves - Intake and/or exhaust valves that are operated by a mechanical linkage.
Priming Cup Priming Cup - A means for introducing fuel directly into the cylinder prior to starting.  The extra fuel provides a richer fuel/air mixture and improves starting reliability.
Ratchet Wheel  Ratchet Wheel - A type of cam that features high and low lobes arranged in a circle.  Rotating the ratchet wheel a fraction of a turn positions either a high lobe or a low lobe to operate linkages or equipment.  Ratchet wheels were sometimes used in gearless engine designs to provide "every other revolution" actuation for engine components such as valves, ignition, and fuel supply.
Screen Cooling  Screen Cooling - A form of evaporative cooling system where water warmed by an engine is pumped over a screen.  The screen breaks the flow of water into smaller droplets to increase the surface area available for convective and evaporative heat transfer.  Water collected below the screen is returned to the engine.  The engine's operator periodically replenishes the supply of water to make up for evaporation.
Side Shaft Side Shaft - A shaft mounted along the cylinder and main frame and used to drive valve gear as well as other engine accessories at the back of the engine.  The side shaft is usually gear driven from the crankshaft and runs at 1/2 engine speed on four-cycle engines.
Slide Valve Slide Valve - An early form of open flame ignition device consisting of a slide with a pocket for carrying a small quantity of burning gas, ignited at atmospheric pressure, to the compressed fuel and air mixture in the cylinder.  Some slides include bleed grooves that allow mixture being compressed in the cylinder to flow into the pocket to feed and maintain the flame prior to the pocket being exposed to the cylinder. The slide shown here has been removed from the engine for clarity.
Stack Music Stack Music - The unique sound produced by an engine's exhaust.
Star Wheel Ignitor  Star Wheel Igniter - A low tension ignition device that uses a rotating contact assembly driven by a toothed wheel and a ratchet mechanism that turns the wheel.
Tapered Connecting Rod Tapered Connecting Rod - A connecting rod machined with a varying cross section, thicker in the middle and thinner at both ends.
Telegraph Wheel  Telegraph Wheel -  A wheel used to adjust the fuel flow to an engine and to provide remote control of the engine.  When drilling or servicing a well, a wire was wrapped around this wheel and another like it back on the rig floor.  The rig's wheel was often fastened to the "headache post," a vertical beam under the rig's walking beam that kept it from crashing down onto the driller in case the rig's pitman arm came loose.  The headache post was close to the driller making it convenient for him to reach and operate the rig's wheel to remotely turn the telegraph wheel on the engine.  The engine clutch, frequently a reversing one, had a long rod back to the same location that gave the driller complete engine control from his position on the rig floor.
Throttle Governing Throttle Governing - A form of engine speed regulation where the energy released in each power cycle is controlled by modulating the flow of fuel, or fuel and air, into the cylinder.  Power cycles in throttle governing occur regularly regardless of engine load.
Timed Hot Tube  Timed Hot Tube - An improved version of a hot tube that has a valve between the cylinder and the tube.  The valve determines when fuel and air mixture from the cylinder flows into the hot tube and provides more precise ignition timing than a simple hot tube.  In this example, a cam driven by the engine side shaft operates the valve.
Wigwag Cam Wigwag Cam - A form of cylindrical cam that has a groove cut in it so that a follower running in the groove will travel across the width of the cam as the cam turns.  Wigwag cams are often designed such that 2 revolutions of the cam are necessary to produce one full back-and-forth motion of the follower across the cam to actuate valve gear on four-cycle engines.  Also known as a crossover cam.
Wipe Spark Igniter Wipe Spark Igniter - A form of low voltage make and break igniter where a moving contact travels past and "wipes" against a stationary contact.  A spark occurs when the moving contact breaks away from the stationary contact.
Valve Chest  Valve Chest - A chamber attached to the cylinder that holds the intake and/or exhaust valves for the cylinder.  A port in the valve chest provides the flowpath to the cylinder.  In some designs, ignition occurs in the valve chest and travels through the port and into the cylinder.

Vaporizer -  A chamber attached to and open to the cylinder that is used to evaporate and heat heavier fuels prior to ignition.  A vaporizer typically operates without cooling so that combustion occurring within the vaporizer maintains its temperature.  Vaporizers are often equipped with burners or torches to provide heating for starting and low load operation.


Engine Arrangement

Early engines are typically classified as horizontal, vertical, or inverted in arrangement based upon the orientation of the cylinder and the direction of piston travel.

Horizontal Engine Horizontal - The cylinder is mounted horizontally and the piston travels horizontally.
Vertical Engine Vertical - The cylinder is mounted vertically and the piston travels vertically with the crankshaft mounted below the cylinder.
Inverted Engine Inverted - The cylinder is mounted vertically and the piston travels vertically with the crankshaft mounted above the cylinder.

Many horizontal engines share a similar arrangement and use a common set of terminology for describing the arrangement.

Near Side of Engine Near Side - The near side of the engine is viewed with the flywheels to the right.  The near side is often the location of the side shaft(s) and other engine accessories.
Off Side of Engine Off Side - The off side of the engine is viewed with the flywheels to the left.

The flywheels are located at the Front of the engine.   The cylinder head is located at the Back of the engine.

Back of engine Front and Back of Engine Front of engine

Engine governors are classified as horizontal and vertical based upon the orientation of the governor's shaft.

Horizontal Governor  Horizontal Governor Head  Vertical Governor  Vertical Governor Head 

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