Important Terms and their Meaning of Mechanical Engineering-Internal Combustion Engine Parts:
AFTER COOLER – A device used on turbocharged engines to cool air which has undergone compression.
ATDC – After TDC, after top dead centre.
AIR CLEANER – A device mounted on the intake manifold for filtering out unwanted solid impurities such as dirt and dust from air that is being drawn into the engine cylinder through the inlet manifold.
AIR COOLED ENGINE – An engine that is cooled by passage of air around the cylinder, not by passage of a liquid through water jackets.
AIR STANDARD CYCLE – A standard cycle of reference by which the performance of the different internal combustion engines may be compared, and their relative efficiencies calculated.
AKROYD ENGINE – The first compression ignition engine, patented by Akroyd Staurt in 1890.
ALUMINIUM CYLINDER BLOCK – An engine cylinder block cast from aluminium or aluminium alloy, and which usually has cast iron sleeves installed for use as cylinder bores.
ANTIFREEZE – A chemical, added to the coolant (usually ethylene glycol) to lower its freezing point and thereby prevent the coolant from freezing in cold weather.
ANTI ICING SYSTEM – A carburettor unit designed to prevent formation of ice on a surface or in a passage.
ARTICULATED CONNECTING ROD – The auxiliary connecting rods of a radial engine, which work on pins carried by the master rod instead of on the main crank-pin. Also called LINK RODS.
BACK PRESSURE – A pressure exerted by a fluid contrary to the pressure producing the main flow. For example, pressure in the exhaust manifold, the higher the back pressure, greater is the resistance to flow of exhaust gases through the exhaust system. This lowers volumetric efficiency.
BARREL – Refers to the cylinders in an engine or to the number of throttle bores in a carburettor.
BARREL TYPE CRANKCASE – A petrol engine crankcase so constructed that the crankshaft can be removed from one end, in more normal construction, the crankcase is split.
BASE CIRCLE – As applied to camshaft, lowest spot on the cam. Area of cam that is directly opposite lobe.
BELLOWS – A device, usually metal that can lengthen or shorten much like an accordion. Some cooling system thermostats are of bellows type.
BIMETAL – A thermostatic bimetal element made up of two different metals with different heat expansion rates. Temperature changes produce a bending or distortion movement of the element.
BLOCK (engine) – Basic part of the engine casting containing cylinders.
BLOWBY – Piston rings do not effectively seal compression pressure, and as such allows hot gases to blow between rings and cylinder wall into the crankcase. This causes overheating of piston and poor performance.
BLOWER – Supercharger or engine intake air compressor, a low pressure air pump, usually rotary or centrifugal type.
BLUE PRINTING (engine) – Dismantling the engine and reassembling it to exact specifications.
BOOST – The amount by which the induction pressure of a super charged internal combustion engine exceeds atmospheric pressure, expressed in kg/sq.cm.
BORE – A cylinder, hole, or the inside diameter of the cylinder or hole. May refer to cylinder itself or to diameter of the cylinder.
BORE DIAMETER – Diameter of a hole or a cylinder.
BORING – Renewing or enlarging cylinders by cutting and honing them to a specified size. Boring bar is used to make the cut.
BORING BAR – Tool used to cut engine cylinders to specific size. As used in garages, to cut worn cylinders to a new diameter.
BOTTOM DEAD CENTER (BDC) – Lowest position of the piston in the cylinder.
BOXED I ROD – Connecting rod in which I beam section has been stiffened by welding plates on each side of the rod.
BRAKE HORSE POWER (BHP) – Actual usable power delivered by an engine at the crankshaft for driving a vehicle or any other unit. Computed using the engine coupled to a dynamometer.
BRAKE MEAN EFFECTIVE PRESSURE (BMEP) – Mean effective pressure (imaginary) which when assumed to be acting on the piston during the power stroke would result in the given brake horse power output. Equal to mean indicated pressure times mechanical efficiency.
BRAKE THERMAL EFFICIENCY – Ratio of heat equivalent of power output in the form of brake horse power to the corresponding heat input from fuel.
BREAKIN – Period of operation between installation of new or rebuilt parts and when the parts are worn to the correct fit. Driving at reduced and varying speed for a specified distance or duration permits parts to wear out to the correct fit.
BREATHER PIPE – A pipe opening into the interior of an engine i.e., crankcase. Used to assist ventilation.
BTDC – Before top dead center, also called BUDC-before upper dead center.
CAM – A rotating lobe of irregular shape or eccentric or offset portion of the shaft (cam). It changes rotary motion of cam shaft to reciprocating or variable motion of valve lifter resting on it.
CAM FOLLOWER (valve lifter) – A part which is held in contact with the cam and to which the cam motion is imparted and transmitted to the push rod.
CAM GROUND PISTON – A piston that is ground slightly oval in shape. It becomes round as it expands with heat.
CAM NOSE – Also called CAM LOBE. That portion of the cam which holds the valve wide open. It is the high point of the cam.
CAM SHAFT – The shaft in the engine which has a series of cam lobes (simply called cams) for operating the valve mechanisms, driven by gears or sprockets and chain from the crankshaft.
CAM SHAFT GEAR – The gear that is fastened to the cam shaft.
CAST IN SLEEVE – An aluminium cylinder block cast around an iron cylinder sleeve.
CAST IRON CYLINDER – A one piece cylinder assembly made of cast iron with a machined bore.
CAST PISTON – A piston made by pouring molten aluminium alloy into the mould of desired shape.
CENTRIFUGAL GOVERNOR – A governor which uses flyweight force to sense speed, in order to control the amount of fuel supplied to the combustion chambers.
CENTRIFUGAL OIL SLINGER – Cup shaped centrifugal oil filter mounted to the end of the crankshaft. As oil passes through the slingers, centrifugal force removes impurities that are heavier than oil.
CHROME PLATED RING – A piston compression or oil ring that has its cylinder wall face lightly plated with hard chrome.
CIRCLIP – A circular clip or snap ring that fits into a groove, used to locate or retain a shaft or component.
CLEARANCE – The amount of space between two moving parts or between a moving and a stationary part, such as a journal and a bearing, piston and cylinder.
CLEARANCE VOLUME – The volume remaining above the piston when the piston is at TDC.
CLOSED CRANKCASE VENTILATION SYSTEM – A system in which the crankcase vapours (blow by gases) are discharged into the engine intake system and pass through the engine cylinder rather than being discharged into the air.
COATED BORE – Thin coating of chrome or iron applied to the inside of the cylinder by electroplating, or wire explosion spray coating.
COATED RING – A piston ring having its cylinder wall face coated with ferrous oxide, soft phosphate or tin. This thin coating helps new rings to seat by retaining oil and reduces scuffing during break-in.
COMBUSTION CHAMBER – The space at the top of the cylinder and in the cylinder head or piston or both, in which combustion of fuel and air charge takes place. The space enclosed by the piston, when the piston is at TDC.
COMBUSTION CHAMBER VOLUME – The volume of the combustion chamber when the piston is at TDC, measured in cubic centimetres.
COMBUSTION CYCLE – A series of thermodynamic processes through which the working gas passes to produce one power stroke. The full cycle is intake, compression, power and exhaust.
COMPRESSION CHECK – Measurement of compression pressure in all the cylinders at cranking speed.
COMPRESSION PRESSURE – Pressure in the combustion chamber at the end of the compression stroke, but without any of the fuel being burned.
COMPRESSION RATIO – The ratio between the total volume of the cylinder when the piston is at BDC and the volume when the piston is at TDC.
COMPRESSION RELEASE – A device to prevent the intake valve or exhaust valve from closing completely. This permits the engine crankshaft to be turned over without compression and with ease. Also called DECOMPRESSOR.
COMPRESSION RINGS – The upper ring or rings on a piston designed to hold the compression in the cylinder and prevent or reduce combustion gas leakage i.e., blowby.
COMPRESSION STROKE – The piston stroke from BDC to TDC during which both valves are closed and the charge is compressed into a smaller space creating heat by molecular action.
COMPRESSION TESTER – An instrument for testing the amount of pressure, or compression, developed in an engine cylinder during cranking. Also called COMPRESSION GAUGE.
CONNECTING ROD – The rod made of steel or aluminium alloy usually having an I beam cross-section. A piston pin connects the connecting rod and the piston.
CONNECTING ROD BEARING – Bearings used in the connecting rod small end or big end holes.
CONNECTING ROD CAP – The part of the connecting rod big end assembly that attaches the rod to the crankpin.
CONNECTING ROD TIP – Amount of radial (side) play at the top of the connecting rod. Measurement of rod tip is one way of determining the condition of the rod big end bearing.
CONTROLLED PORT SCAVENGING – Scavenging method using ports which are controlled by valves in addition to the power piston.
COOLANT – The liquid mixture of antifreeze and water circulated in the cooling system of an engine or machinery.
COOLING SYSTEM – In an engine, the system that removes heat by the natural or forced circulation of the coolant and thereby prevents engine overheating. It includes the water jackets, water pump, radiator and thermostat, or cooling fins, blower and cowl.
CORE (radiator) – A number of coolant passages surrounded by fins through which air flows to carry away heat from the coolant.
COUNTER FLOW CYLINDER HEAD – has the intake and exhaust passages on the same side of the cylinder head.
COUNTER WEIGHT – Weights that are mounted on the crankshaft opposite each crank throw. These reduce the vibration caused by the crank and also reduce bearing loads due to inertia of the moving parts.
CRANK – A device for converting reciprocating motion into rotary motion or vice versa.
CRANKCASE – The lower part of an engine in which the crankshaft rotates. It consists of the lower section of the cylinder block, and the oil pan.
CRANKCASE VENTILATING SYSTEM – The system that permits air to flow through the engine crankcase when the engine is running to carry out the blow by gases and relieve any pressure build up.
CRANKPIN – That part of the crank throw of the crankshaft to which the connecting rod is attached.
CRANKPIN RIDGING – A type of crankpin failure typified by deep ridges worn into the crankpin bearing surfaces.
CRANKSHAFT – The main rotating member or shaft running along the length of the engine. Portions of the shaft are offset to form throws or cranks to which the connecting rods are attached. Crankshaft is supported by main bearings.
CRANKSHAFT AXLES – Extension at each end of the crankshaft to provide a mounting place for main bearings, and alternator rotor of magneto flywheel.
CRANKSHAFT GAUGE – A special type of micrometer which can measure crankshaft wear without removing the crankshaft from the block.
CRANKSHAFT GEAR – A gear or sprocket, mounted on the front of the crankshaft. Used to drive the camshaft gear or chain.
CRANKSHAFT WHEEL – Portions of an assembled crankshaft, in the form of wheels that provide a mounting place for crankpin and crank-axles.
CRANK THROW – One crankpin with its two webs (the amount of offset of the journal).
CRANK WEB – The portion of the crank throw between the crankpin and main journal. This makes up the offset.
CRITICAL SPEEDS – Speeds at which the frequency of the power strokes synchronize with the crankshafts natural frequency. If the engine is operated at one of its critical speeds for any length of time, a broken crankshaft may result.
CROSS FLOW CYLINDER HEAD – has the intake and exhaust lines on opposite sides of the cylinder head.
CYCLE – A series of events which continuously repeat in definite order. In an engine, the cycle constitutes the four operations that complete the working process and produce power.
CYLINDER – A round hole or tubular shaped structure in a block or casting in which a piston reciprocates.
CYLINDER BLOCK – The basic framework of the engine to which the other engine parts are attached. It includes the engine cylinders and the upper part of the crankcase.
CYLINDER BORE – Diameter of cylinder opening.
CYLINDER BORING – Bore diameter in a cylinder machined to accept oversize piston. This renews a worn cylinder.
CYLINDER DEGLAZING – Use of a hone to slightly roughen the cylinder walls. It produces a cross hatch pattern which aids in seating of new rings.
CYLINDER HEAD – The part that encloses the cylinder bores, used to cover tops of cylinders. Metal section bolted on top of block. It contains the water jackets, and on I head engines, the valves. Also forms part of combustion chamber.
CYLINDER HONE – An expandable rotating tool with abrasive fingers turned by an electric motor, used to clean and smooth the inside surface of a cylinder to exact measurements.
CYLINDER LEAKAGE TESTER – A type of cylinder tester that forces compressed air into the cylinder through the sparkplug hole when the valves are closed and the piston is at TDC on the compression stroke. The percentage of compressed air that leaks out is measured, and the source of leakage accurately pin points the defective part.
CYLINDER SLEEVE – A replaceable sleeve, or liner, put into the cylinder block to form the cylinder bore. It is either pressed or pushed into the cylinder block.
DEAD CENTER – Point at which the piston reaches its uppermost or lowermost position in the cylinder. At these positions, at the end of the stroke, the crank and connecting rod are in a straight line.
DECARBONIZE – To remove carbon build up on piston, combustion chamber and other parts.
DECOMPRESSOR – is the device that opens the engine intake or exhaust valve and retains it in the opened position. The compression effect is thus reduced and helps easy rotation of the crankshaft at the time of starting.
DIPSTICK – The metal stick that passes into the oil sump. Used to determine quantity of oil in the engine sump.
DIRECT COOLED PISTON – A piston which is cooled by the internal circulation of a liquid.
DISPLACEMENT – In an engine, the total volume of fresh charge an engine is theoretically capable of drawing into all cylinders during one operating cycle. The space swept through by the piston in all cylinders in moving from one end of a stroke to the other.
DOHC ENGINE – An engine having two camshafts over each line of cylinders, one operating intake valves, and the other operating exhaust valves. Double overhead camshaft engine.
DRY SLEEVE – A cylinder sleeve (liner) where the sleeve is supported in the cylinder block metal over its entire length. The coolant does not touch the sleeve itself.
DYNAMOMETER – A device for absorbing and measuring the power output, or brake horse power, of an engine. May be an engine dynamometer, which measures power output at the flywheel, or a chassis dynamometer, which measures the power output at the driven wheels.
ELEMENT FILTER – A disposable oil or air filter that uses gauze or paper as filtering material.
ENBLOCK – One piece, such as an engine cylinder block cast in one piece.
ENGINE – A machine that converts heat energy into mechanical energy (mechanical action in a car). The assembly that burns fuel to produce power, sometimes referred to as the power plant.
ENGINE DISPLACEMENT – Volume of space through which head of piston moves in full length of its stroke multiplied by the number of cylinders in the engine. Result is given in cubic centimetres.
ENGINE TUNE UP – The procedure for checking and adjusting the various engine components so that the engine is restored to top operating condition.
ETHYLENE GLYCOL – A chemical compound (solution) added to the engine coolant to reduce its freezing point and thereby protect the cooling system against freezing of the coolant.
EXHAUST CUTOUT – Y shaped device placed in the exhaust pipe of an engine ahead of muffler. Driver may channel exhaust through the muffler or into the other leg of the Y where the exhaust gases pass out without going through the muffler.
EXHAUST MANIFOLD – A housing with a series of connecting pipes between the exhaust ports and the exhaust pipe through which hot burned gases from the engine cylinders flow.
EXHAUST PIPE – Pipe connecting exhaust manifold to the muffler.
EXHAUST PORT – The opening through which exhaust gases pass from the cylinders to the manifold.
EXHAUST STROKE – The piston stroke from BDC to TDC during which the exhaust valve is open so that the burned gases are forced out from the cylinder.
EXHAUST SYSTEM – A group of parts consisting of the exhaust manifold, exhaust pipe, muffler, tailpipe and resonator if used.
EXHAUST TUNING – Cutting exhaust pipe to such length that provides maximum efficiency.
EXHAUST VALVE – The valve which opens to allow burned gases to exhaust from the engine cylinder into the exhaust manifold during the exhaust stroke.
EXPANSION PLUG – A plug that is slightly dished out and used to seal core passages in the cylinder block and cylinder head. When driven into place, it is flattened and expanded to fit tightly.
EXPANSION RATIO – Ratio of the total volume when the piston is at BDC to the clearance volume when the piston is at TDC (normally equal to compression ratio).
EVAPORATIVE COOLING SYSTEM – A cooling system in which the heat finally passes to atmosphere by evaporation of the coolant. This system may be either open or closed.
FAN (cooling) – The device on the front of the engine that rotates to draw cooling air through the radiator or around the engine cylinders.
FAST IDLE – Engine idle speed when the carburettor fast idle cam is in operation. A mechanism on the carburettor, connected to the automatic choke, that holds the throttle valve slightly open when the engine is cold so that the engine will idle at the higher rpm as long as the choke is applied.
F HEAD ENGINE – A type of engine in which some of the valves are in the cylinder head and some in the cylinder block, giving the F shaped appearance.
FILTER – That part in the air, lubricating oil or fuel system through which air, oil or fuel must pass so that dust, dirt or other contaminants are removed.
FINS (engine) – Thin metal projections on an air cooled engine cylinder and head, which greatly increase the heat radiating surfaces and help cooling of the engine cylinder.
FINS (radiator) – Thin metal projections, over which cooling air flows, that carry heat away from the hot coolant passages to the passing air.
FIRING ORDER – The numerical order in which the engine cylinders fire, or deliver their power strokes begining with No.1 cylinder.
FLYWHEEL – A heavy rotating metal wheel attached to the crankshaft which helps even out the power surges from the power strokes and also serves as part of the clutch and engine cranking system. Acts as power reservoir.
FLYWHEEL RING GEAR – A gear fitted around the flywheel that is engaged by the teeth on the starting motor drive to crank the engine.
FORGED PISTON – A piston made by hammering hot aluminium into a mould of desired shape.
FOUR STROKE CYCLE – The four piston strokes of intake, compression, power and exhaust which make up the complete cycle of events in the four stroke cycle.
FRICTION HORSE POWER – The power used up by an engine in overcoming its own internal friction, usually, it increases as engine speed increases.
FUEL TANK – The storage tank for fuel on the vehicle.
FULL FLOATING PISTON PIN – is one which is free to rotate both in the piston pin bosses and in the connecting rod small end.
FULL FLOW FILTER – Type of oil filter in which all the oil from the oil pump flows through the filter.
GASKET – A flat strip, usually of cork or other material, placed between two non-moving, machined surfaces to provide a tight seal between them and thereby prevent leakage.
GASKET CEMENT – A liquid adhesive material, or sealer applied on gaskets, in some applications, the liquid layer of gasket cement is used as the gasket itself.
GLAZE (cylinder) – The mirror like, very smooth finish that develops on engine cylinder walls during engine operation.
HEAT DAM – In a piston top land a groove cut out to reduce the size of the heat path, allowing the piston skirt to run at lower temperature.
HEAT LAND RING – A compression ring having the cross-sectional shape of the letter L, used as top ring.
HELICOIL – A rethreading device to repair worn or damaged threads. It is installed in a retapped hole to bring the screw thread down to the original size.
HORSE POWER (hp) – A measure of the mechanical power, or the rate at which work is done. One horse power equals 4500 m.kg of work per minute.
IDLE SPEED – The speed at which an engine runs without load when the accelerator pedal is released.
I HEAD ENGINE – An overhead valve (OHV) engine with the valves in the cylinder head.
IMPELLER – Finned wheel that produces pressure and flow when spun in an enclosed housing of oil pump or water pump.
INDICATED HORSE POWER (IHP) – The power produced within the engine cylinders before deducting any frictional loss.
INERTIA – Tendency of a stationary object to resist movement or tendency of a moving object to continue moving in same direction.
IN LINE ENGINE – An engine in which all engine cylinders are in a single row, or line.
INTAKE MANIFOLD – is a casting attached to the cylinder head in the case of a overhead valve engine or to the cylinder block in the case of a side valve engine. Through the intake manifold fresh charge enters the cylinders.
INTAKE STROKE – The piston stroke from TDC to BDC during which the intake valve is open and the cylinder receives a charge of air fuel mixture in a SI engine or air alone in a CI engine.
INTAKE VALVE – The valve that opens to permit fresh charge to enter the cylinder on the intake stroke.
INTERNAL COMBUSTION ENGINE (IC engine) – An engine in which the fuel is burnt inside the engine.
JACKETS – The water jackets that surround the cylinders through which the coolant passes.
KINETIC ENERGY – Energy associated with motion. An internal combustion engine produces kinetic energy (crankshaft rotation).
L HEAD ENGINE – A type of engine with valves located in the cylinder block, the combustion chamber is L shaped.
LIGHT LOAD TEST – The test applied to storage batteries during which the voltage is measured while the battery is subjected to a light load, such as the car head lights.
LIQUID COOLED ENGINE – An engine that is cooled by the circulation of the liquid coolant around the cylinders.
LOAD TEST – A cranking motor test to measure the current drawn under normal cranking load.
MAIN BEARINGS – The cylinder block and crankcase unit is provided at the bottom with split main bearings for supporting the crankshaft journals.
MANIFOLD – Intake manifold or exhaust manifold. A casting connecting a series of outlets to a common opening.
MECHANICAL EFFICIENCY – In an engine, the ratio between brake horse power and indicated horse power.
MUFFLER – In the exhaust, a device through which the exhaust gases must pass and which muffles the sound.
NO LOAD TEST – A cranking motor test in which the cranking motor is operated without load, the current drawn and the armature speed at the specified voltage are noted.
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.
PANCAKE ENGINE – An engine with two rows of cylinders which are opposed and on the same plane, usually set horizontally in a vehicle.
PISTON – A cylindrical part, closed at one end, which moves up and down in the cylinder. Open end is attached to the connecting rod. Combustion pressure is exerted on closed end of piston, causing connecting rod to move and crankshaft to turn.
PISTON CROWN – Top of piston, directly exposed to combustion pressure and heat.
PISTON DISPLACEMENT – The cylinder volume displaced by the piston as it moves from the bottom to the top of the cylinder during one complete stroke.
PISTON PIN – Also called wrist pin. The cylindrical or tubular metal piece that attaches the piston to the connecting rod.
PISTON PIN BOSS – A strengthened section of piston wall extending to inside of piston crown. It supports piston pin.
PISTON PIN HOLE – Machined hole through piston wall where piston pin and retaining circlips are mounted.
PISTON RINGS – Rings fitted into grooves in the piston. These are two types: Compression rings for sealing the compression into the combustion chamber and oil rings to scrape excess oil off the cylinder wall and thereby prevent it from working up into and burning in the combustion chamber.
PISTON RING COATINGS – of relatively soft substances such as phosphate, graphite, and iron oxide aid effective wear in and prevents rapid wear of the ring.
PISTON RING COMPRESSOR – A special tool used in engine overhaul work to compress the piston rings inside the piston grooves so that the piston and rings assembly may be installed in the engine cylinder.
PISTON RING END GAP – Distance between ends of a piston ring when installed in the cylinder. The clearance is measured with a feeler gauge, keeping the piston at BDC.
PISTON RING GROOVE – Grooves machined in the piston external surface to accept piston rings.
PISTON SEIZURE – Overheating of piston to the point where it will no longer move freely in the cylinder.
PISTON SKIRT – The lower part of the piston below the piston pin hole.
PISTON SLAP – A hollow, muffled, bell like sound made by an excessively loose piston slapping the cylinder wall at dead centre positions.
POPPET VALVE – A mushroom shaped valve widely used in internal combustion engines.
PORT (cylinder) – In an engine, the valve port or opening in which the valve operates and through which the charge or burned gases pass.
POWER – Rate at which work is done.
POWER PLANT – The engine or power producing mechanism in the vehicle.
POWER STROKE – The piston stroke from TDC to BDC during which the charge burns and forces the piston down so that the engine produces power.
PRESSURE TESTER – An instrument that clamps in the radiator filler neck, and is used to pressure test the cooling system for leaks.
PREVENTIVE MAINTENANCE – The systematic inspection, detection and correction of failures in an engine or in a vehicle, either before they occur, or before they develop into major defects.
PUSH ROD – In the I head engine, the rod between the valve lifter and rocker arm.
RADIATOR – A heat exchanger which reduces coolant temperature in a liquid cooling system.
RADIUS RIDE – In a reground crankshaft, if the radius of the journal, where it comes up to the crank cheek, is not cut away enough, the journal will ride on the edge of the bearing. The contact is called radius ride.
REBORE – To bore out a cylinder larger than its original size.
RECIPROCATING ENGINE – Also called piston engine. An engine in which the piston moves up and down or back and forth, as a result of combustion in the top of the cylinder.
RING EXPANDER – A special tool used to expand piston rings for installation on the piston.
RING LAND – Solid area of piston which supports rings, located between ring grooves.
RING RIDGE – A ridge left at the top of a cylinder as the cylinder wall below it is worn by piston ring movement.
RING RIDGE REMOVER – A special tool used for removing the ring ridge from the cylinder.
ROCKER ARM – In an I head engine, a device that rocks on a shaft or pivots on a stud as the cam actuates the push rod causing the valve to open.
ROD BOLTS – Special bolts used on the connecting rod to attach the cap. Sometimes lock nuts are provided.
ROD SMALL END – The end of the connecting rod through which a piston pin passes to connect the piston to the connecting rod.
ROD BIG END – The end of the connecting rod that attaches around the crankpin.
RPM – Revolutions per minute.
REVERSE FLUSHING – A method of cleaning a radiator or an engine cooling system by flushing in the direction opposite to normal coolant flow.
SCORED – Scratched or grooved, as a cylinder wall may be scored by abrasive particles moved up and down by the piston rings.
SCRAPER – A device in engine service, to scrape carbon etc., from engine block, piston etc.
SCRAPER RING – On a piston, a type of oil control ring designed to scrape excess oil from cylinder wall and cause it to flow down into the crankcase.
SCREEN – A fine mesh screen in the fuel or lubricating systems that prevents large particles (dirt and particles of dust) from entering the system.
SCUFFING – A type of wear of moving parts characterized by transfer of material from one to other part and results in pits and grooves.
SEALER – A thick, tacky compound usually spread with a brush, which may be used as a gasket or sealant, to seal small openings or surface irregularities.
SEAT – The surface on which another part rests, such as a valve seat. Also, applied to the process of a part wearing into fit, for example piston rings seat after a few kilometers of driving.
SEMIFLOATING PISTON PIN – is clamped in the piston pin bosses and free to rotate in the connecting rod small end or clamped in the connecting rod small end and free to rotate in the piston pin bosses.
SEVERE RINGS – Piston rings which exert relatively high pressure against the cylinder walls, sometimes by the use of an expander spring behind the ring. Such rings can be used in an engine having excessive cylinder wear.
SHROUD – A hood placed around an engine cooling fan to improve fan (cooling) action.
SIAMESED CRANKSHAFT – Crankshaft configuration where two rods are mounted on the same crankpin (journal). One rod is forked and the other rod is mounted on inside of the fork.
SIDE BY SIDE CRANKSHAFT – Crankshaft configuration where connecting rods are mounted next to each other on the same crankpin (journal).
SINGLE PIECE CONNECTING ROD – has small end, rod or shank and big end as one unit. This is used in most of the small two stroke engines meant for two wheelers.
SPRING (valve) – A coiled wire that varies its length by flexing, and twisting.
SPRING FREE LENGTH – The length of the spring when measured without any load on it.
SPRING MECHANICAL PRELOAD – The length or pressure of a spring, measured while it is in the installed condition.
SPRING RATE – The amount of force necessary to compress a spring a specific distance, kilograms per centimetre, to indicate the stiffness or softness of a spring.
SPRING RETAINER – In the valve train, the piece of metal that holds the springs in place and is itself locked in place by the valve spring retainer locks.
SPRING RETAINER LOCK – The locking device on the valve stem that locks the spring retainer in place.
SQUARE ENGINE – An engine having the bore and stroke of equal measurements.
SQUISH – The action (radial inward air motion) in some combustion chambers in which the last part of the compressed charge is pushed, or squirted, out of a decreasing space between the piston and the cylinder head.
STIRLING ENGINE – A typical internal combustion engine in which the piston is moved by the changing pressure of a working gas that is alternately heated and cooled.
STROKE – In an engine, the distance that the piston moves from BDC to TDC or vice versa.
SUMP – A system for storing lubricating oil, either in the crankcase (wet sump) or in a separate tank (dry sump).
SUPER CHARGER – A device in the intake system of an engine which pressurizes the ingoing charge. This increases the mass of charge (air fuel mixture) burned and thus increases engine output. If the supercharger is driven by the engine exhaust gas turbine, it is called TURBOCHARGER.
TANK UNIT – The unit of the fuel indicating system that is mounted in the fuel tank.
TAIL PIPE – carries the exhaust gases from the muffler and exhausts the same into the atmosphere. The tail pipe end is sometime cut on a bias (at an angle) to reduce exhaust noise.
THERMAL EFFICIENCY – Relationship between the power output and the energy in the fuel burned to produce the output.
THERMOSTAT – A temperature sensitive device used in a cooling system to adjust flow of coolant as coolant temperature changes.
THERMOSTATICALLY CONTROLLED AIR CLEANER – An air cleaner which uses a thermostat to control the preheating of intake air.
THROW A ROD – Expression used to designate an engine with a loose, knocking connecting rod bearing, or an engine that has broken a connecting rod and showed it through the cylinder block or oil pan.
TIMING – In the engine, refers to timing of valves, and timing of ignition, and their relation to piston position in the cylinder.
TIMING CHAIN – A chain driven by a sprocket on the crankshaft, that drives the sprocket on the camshaft.
TIMING GEARS – are a pair of meshing gears (one bigger gear mounted on the camshaft and another smaller gear mounted on the crankshaft) meant for driving the camshaft at the required speed ratio by the crankshaft.
TOP DEAD CENTRE (TDC) – The piston position at which the piston has moved to the top of the cylinder and the centre line of the connecting rod is parallel to the cylinder wall.
TORQUE – The twisting force at the end of the crank shaft multiplied by the distance of this force application from the shaft centre, measured in kilogram meters or Newton meters.
TORSIONAL VIBRATION – Back and forth motion around a turning centre. Vibration in a rotary direction that causes a twist-untwist action on a rotating shaft, a rotating shaft that repeatedly moves ahead or lags behind the remainder of the shaft; for example, the actions of a crankshaft responds to the cylinder firing impulses.
TUNED INTAKE SYSTEM – An intake system in which the manifold has the proper length and volume to introduce a ramjet or supercharging effect.
TUNE UP – The procedure of inspection, testing and adjusting an engine and replacing any worn parts to restore the engine to its best performance.
TURBOCHARGER – A supercharger driven by the gas turbine which is operated by the engine exhaust gases.
TWO STROKE CYCLE – The series of events namely intake, compression, power and exhaust all of which take place in two piston strokes. Also called TWO CYCLE in a short form.
V ENGINE – An engine with two banks of cylinders set at an angle to each other to form a V.
VALVE – A device that can be opened or closed to allow or stop the flow of a fluid (liquid or gas or vapour) from one to another place.
VALVE CLEARANCE – The clearance between the rocker arm and the valve stem tip in an overhead valve engine: The clearance in the valve train when the valve, is in the closed position. Also called VALVE LASH.
VALVE FLOAT – The condition that exists when an engine valve does not follow the cam profile, failure of the valve to close at the proper time.
VALVE GRINDING – Refacing a valve in a valve facing machine.
VALVE GUIDE – The cylindrical part in the cylinder block or head in which the valve is assembled and in which valve stem moves up and down.
VALVE LIFTER – Also called lifter, tappet, valve tappet and cam follower. A cylindrical part of the engine, which rests on a cam of the camshaft and is lifted, by cam action, so that the valve is opened.
VALVE LIFTER FOOT – The bottom end of the valve lifter, the part that rides on the cam lobe.
VALVE OVERLAP – Number of degrees of crankshaft rotation through which both the intake and exhaust valves are open together.
VALVE ROTATOR – Device used in place of the valve spring retainer, it has a built in mechanism to rotate the valve slightly each time it opens.
VALVE SEAT – The surface in the cylinder head or cylinder block against which the valves face comes to rest.
VALVE SEAT INSERT – Metal rings inserted in the valve seats, usually exhaust, they are of special metal which can withstand high temperature and exhibit minimum wear at these temperatures.
VALVE SEAT RECESSION – Also known as lash loss, the tendency for the valves, in some engines run on unleaded gasoline, to contact the seat in such a way that the seat wears away, or recesses into the cylinder head.
VALVE STEM – The long, thin cylindrical section of the valve that fits and moves in the valve guide.
VALVE TIMING – The timing of valve opening and closing in relation to piston position in the cylinder.
VALVE TRAIN – The valve operating mechanism of an engine, from the camshaft of the valve.
VEE CYLINDERS – Cylinders positioned at angles to each other forming the shape of the letter V.
VIBRATION DAMPER – is attached to the crankshaft in order to control the torsional vibration caused by the power impulses.
VOLUMETRIC EFFICIENCY – Ratio between the amount of fresh charge that actually enters an engine cylinder and the theoretical amount that could enter under ideal conditions.
WANKEL ENGINE – A rotary type engine, in which a three lobe rotor turns eccentrically in a specially shaped housing.
WET LINER – When fitted in the cylinder block has water on the external surface of the liner. Good cooling is realized by having the water in direct contact with the liner.
WRIST PIN – A cylindrical (solid or hollow) pin that attaches the piston to the connecting rod.