ONE WAY CLUTCH – A clutch that holds in one direction but allows movement in another direction.

OVER DRIVE – A device in the power train of some vehicles that introduces an extra set of gears into the power train. This causes the propeller shaft to overdrive or drive faster than the engine crankshaft. Engine speed is thus reduced without reduction of vehicle speed.

OVER RUNNING CLUTCH – A type of clutch that will transmit rotary motion in one direction only, when rotary motion attempts to pass through in other direction, then the driving member over runs and does not pass motion to the other member.

OVER STEER – The tendency of a vehicle to turn sharper than the turn selected by the driver.

OPEN COMBUSTION CHAMBER – A type of diesel combustion chamber in which all the air meant for combustion is confined in one space and combustion of entire fuel takes place within this space. Also called DIRECT INJECTION CHAMBER or QUIESCENT CHAMBER.

OPEN TYPE NOZZLE – A simple spray nozzle open to the cylinder but with a check valve which prevents the high pressure gases in the engine cylinder from passing to the pump.

OPTIMUM INJECTION ADVANCE – Fuel injection timing before TDC which will result in minimum ignition delay.

ORDERLY TURBULENCE – Air motion which is controlled as to direction and velocity.

ODDSIDE – Support used for supporting a pattern whilst the drag is being rammed up.

OPEN SAND CASTING – A casting poured in a mould which has no cope or other covering.

OIL STONE – An abrasive stone that is oiled and used to sharpen cutting tools.

ONE DIMENSIONAL FLOW – The fluid flow in which the variables are constant over any cross-section of the flow.

OPEN CYCLE TURBINE – Turbine in which the heat is transferred by direct combustion and after doing work in the turbine, the gases are exhausted into the atmosphere.

OVERALL EFFICIENCY OF JET PROPULSION – Product of the propulsion efficiency of the jet unit and the thermal efficiency of the jet unit.

OVERALL EFFICIENCY OF PROPELLER UNIT – Product of the propeller (propulsion) efficiency, thermal efficiency of the engine (power turbine) and the transmission efficiency from prime mover to propeller shaft.

OVERALL TURBINE EFFICIENCY – Ratio of the delivered shaft work (power) to the ideal energy available from the medium.

ORANGE PEEL – A pebble grained surface which develops in forming of metals having coarse grains.

ORE – A natural mineral that may be mined and treated for the extraction of any of its components, metallic or otherwise.

OSMIUM – Osmium is the heaviest of all metals (sp gr. 22. 48), which melts at 4900°F and is harder than glass and quartz.

OIL – A liquid lubricant derived from crude oil used to provide lubrication between moving parts.

OIL CLEANER – The filtering device through which oil passes, which filters dirt and dust from the oil.

OIL CONSUMPTION – Oil pumped into the combustion chamber of an engine by the piston and rings and burnt there in a given time.

OIL CONTROL RINGS – The lower ring or rings on the piston of an engine, designed to prevent excessive amounts of oil from working up into the combustion chamber.

OIL COOLER – A small radiator through which the oil flows to lower its temperature.

OIL DILUTION – Dilution of oil in the crankcase of a SI engine, by leakage of liquid gasoline from the combustion chamber past the piston rings.

OIL FILTER – Unit in the lubrication system through which oil passes to remove any impurities from oil. It may be paper, wire screen or rotor designed to keep oil clean.

OIL LEVEL INDICATOR – The indicator usually called the dipstick, that can be removed to determine the level of oil in the crankcase of an engine or machine.

OIL PAN – The detachable lower part of the engine made of sheet metal, which encloses the crankcase and acts as an oil reservoir.

OIL PASSAGES – Holes and passages drilled in the block and in the engine parts through which oil flows.

OIL PRESSURE GAUGE – An instrument used to measure and indicate the amount of oil pressure in the lubrication system.

OIL PUMP – In the lubricating system, the device that delivers oil from the oil pan to the various moving engine/machine parts.

OIL PUMP BLEEDING – Removal of air from the supply line and the pump in a two stroke cycle oil injection system.

OIL PUMPING – Passing of oil past the piston rings into the combustion chamber because of defective rings, worn cylinder walls etc.

OIL RESERVOIR – That space in the base of the oil separator where oil is accumulated prior to its return to the pump.

OIL SEAL – A seal placed around a rotating shaft or other moving part, to prevent passage or escape of oil.

OIL SEAL AND SHIELD – Two devices used to control oil leakage past the valve stem and guide into the ports or the combustion chamber.

OIL SPILL RING – Collars or oil throw rings put on the rotating shaft, prevent oil leakage along the shaft, utilizing the increase of centrifugal force with the increase of diameter.

OIL STRAINER – A wire mesh screen placed at the inlet end of the oil pump pickup tube to prevent dirt and other large particle from entering the oil pump.

OUTER RACE – In a roller/ball bearing assembly, the stationary part that supports the rotating load on the bearing.

OXIDIZED OIL – Oil that has been chemically combined with oxygen as a result of excessive heat, oil agitation, and exposure to combustion contaminants.

OCTANE RATING – The measure of antiknock property of gasoline. The higher the octane rating, (OCTANE NUMBER), the more resistant the gasoline is to knocking or detonation and better the quality: Higher compression engines require higher octane gas.

OCTANE NUMBER OF A FUEL – is the percentage by volume of isooctane in a mixture of iso-octane (C8H18) and n-heptane (C7 H16) which will exhibit the same antiknock characteristic of the fuel under test when tested in a standard CFR variable compression ratio engine, under a set of standard test conditions.

OIL BURNER – Any device wherein oil fuel is vaporized or so called atomized and mixed with air in proper proportion for combustion.

ORGANIC FINISHING – Coating a surface with a continuous film of an organic material for protecting the surface from corrosive influences, for enhancing the appearance or a combination of both.

ORGANIC FINISHING – Coating a surface with a continuous film of an organic material for protecting the surface from corrosive influences, for enhancing the appearance or a combination of both.

OIL CONTROL RING – Piston ring designed to remove excess oil from the cylinder wall, usually bottom ring.

OIL SUMP – is fastened to the bottom of the crankcase. This protects the engine from below and is used as a reservoir for lubricating oil in a four stroke engine.

OPPOSED CYLINDERS – Cylinders positioned opposite each other in the same plane.

O RING – A circular cross-sectional sealing ring, which is compressed into the groove to provide sealing action. Seal used in dynamic application where little or no rotational motion occurs. Also used as a static seal.

OTTO CYCLE – The four operations, namely intake, compression, power and exhaust form a cycle. Named after the inventor Nikolas Otto and is the basic cycle for all SI engines.

OVERCHARGING – Continued charging of a battery after it has reached a charged condition. This action damages the battery and shortens its life.

OVERHEAD CAMSHAFT (OHC) ENGINE – An engine in which the camshaft is located in the cylinder head or heads instead of in the cylinder block.

OVERHEAD VALVE (OHV) ENGINE – An engine in which the valves are mounted in the cylinder head above the combustion chamber, the camshaft is usually mounted in the cylinder block, and the valves are actuated by push rods.

OVER SQUARE ENGINE – An engine which has a bore larger in dimension than the length of the stroke.

ODD LEG – Caliper having one leg bent inwards at its ends, like the two legs on a pair of inside calipers, the other leg being pointed or having a separate hardened point attached to it.

OPTICAL FLAT – Plate generally made of glass or quartz and used as a standard of reference as a flat surface.

OPTICAL PROTRACTOR – Angle measuring instrument fitted with a scale read by an optical magnifying device.

OVERARMS – Adjustable supports for the end of a milling cutter arbor farthest from a milling machine spindle.

OIL COOLER – A heat exchanger for lowering the temperature of oil.

OIL PUMP – Mechanical device to pump oil (under pressure) into the various oil galleries.

OPTICAL COMPARATOR – A machine that enlarges the profile view of a part and compares it to a standard profile.

OSCILLOSCOPE – A device for recording wave forms on a fluorescent screen, proportional to the input voltage.

OVER RUNNING CLUTCH – A clutch mechanism that transmits power in one direction only.

OVER SPEED GOVERNOR – A governor that shuts off the fuel or stops the engine, only when excessive speed is reached.

OFF CENTER – Not on the true center line or axis, offset, eccentric or inaccurate.

OPEN HOPPER – A freight car with an open top and collapsible bottom.

ORDINARY LAY ROPE – A rope in which the direction of twist of wires is opposite to that of the strands in the rope.

ORDINARY (untwisting) ROPES – Ropes in which the wires and strands fail to retain their position once the wire sizings are removed from the ends and consequently, these ropes tend to untwist.

ORIGINATING CARRIER – The first carrier to receive the goods from the shipper.

OVERHEAD BRIDGE CRANE – A shop floor unit consisting of a trolley or crab equipped with a hoisting mechanism, a bridge travelling on wheels fitted to end carriages and supported by track rails, which in their turn are fixed to rail supports provided either at the top of the shop walls or columns.

OVER LOAD PROTECTION DEVICE – Units provided on the hoisting motion that automatically cut out the hoisting motor on jib and tower cranes when the excess of load lifted is not less than 10 per cent of the rated capacity.

OILINESS – The capacity of the lubricant to stick on to the surface under conditions of heavy load.

OXIDATION – The slow or rapid reaction of oxygen with other elements, burning. In metals, over oxidation during heating under oxidizing conditions often results in permanent damage to metals.

OXIDATION REDUCTION – A chemical reaction in which one or more electrons are transferred from one atom or molecule to another.

OPEN DIE FORGING or SMITH FORGING – A forging process in which a drop hammer delivers blows of great force to a heated metal that is shaped by manipulating it under the hammer.

OXY ACETYLENE CUTTING – A method of cutting heavy iron or steel plates with the aid of an oxyacetylene torch.

OLDHAM COUPLING – A mechanism for connecting two shafts having parallel misalignment. The coupling transmits a constant velocity ratio.

OIL FAILURE RELAY – An oil pressure switch inserted in the compressor lubricating system and wired to shut down the machine in the event of an oil failure.

OIL SEPARATOR – Device used to separate oil from the refrigerant gas, returning the oil to the compressor and allowing the refrigerant to continue on its circuit through the refrigerating system.

OPEN SYSTEM – Chilled water is sprayed into the air to be cooled and it is then collected in the air washer tank and returned to the flash tank and is again cooled.

OPERATING CONTROLS – Sensitive to changes in the desired conditions such as temperature (or its related pressure) and humidity.

OCTANE NUMBER OF A FUEL – is the percentage by volume of isooctane in a mixture of iso-octane and n-heptane which will exhibit the same antiknock characteristic of the fuel under test, when tested in a standard (CFR) engine, under a set of standard test conditions.

OCTANE RATING – The number indicating the quality of gasoline based on its ability to resist knock. The higher the number, the better the quality. Higher compression engines require higher octane fuel.

OPTIMUM SPARK TIMING – is the ignition timing which will cause that half of the pressure rise occurs at dead center. This happens in practice when 75 percent of the charge burns after ignition.

ONCE THROUGH BOILER – A boiler or steam generator which receives feed water at one end of continuous tubes and discharges steam at the other end.

OPEN HEATER – An open chamber in which the exhaust steam and water to be heated are brought into intimate contact by spraying the water through the steam, both the water and condensate going to the boiler.

OVER EXPANDING – A nozzle which operates with a back pressure above the designed value of pressure at the exit of the nozzle.

OVERALL THERMAL EFFICIENCY – Ratio of the useful heat drop to the heat supplied in a turbine.

OPEN SYSTEM – It has no closed boundary, but has one or more openings. Fluid may enter or leave the system, it undergoes thermodynamic process, while moving through the system.

O-RING CHAIN – Roller chain which uses ‘O’ rings to permanently seal lubricant into area between pins and bushings.

OUTPUT SHAFT – Gearbox shaft that transmits power to final drive at a selected ratio.

OVERALL GEAR RATIO – Ratio of crankshaft revolutions to rear wheel revolutions.

OVER WELDING – Depositing more filler metal than required.

OXYACETYLENE CUTTING – Process that severs metals by the chemical reaction of oxygen with the base metal at elevated temperatures caused by combustion of acetylene with oxygen.

OXYACETYLENE WELDING – Process that produces coalescence of metals by heating them with the flame obtained by combustion of acetylene with oxygen.

OXY FUEL CUTTING – A group of cutting processes used to sever metals by means of the chemical reaction of oxygen with the base metal at elevated temperatures produced by flames obtained from combustion of fuel gas and oxygen e.g., oxy hydrogen cutting, oxy natural gas cutting, oxy propane cutting.

OXY FUEL GAS WELDING – A group of welding processes that produces coalescence by heating materials with an oxyfuel gas flame or flames with or without the application of pressure and with or without the use of filler metal e.g., oxy hydrogen welding.

OXYGEN LANCE CUTTING – An oxygen cutting process used to sever metals with oxygen supplied through a consumable lance. The preheat to start cutting is obtained by other means.