_TERMINE_RELATIVO_MOTORI_DI_AUTOMOBILI_(INGLESE)
_SPIEGAZIONE_DEL_TERMINE_(INGLESE)
ABS
A DEVICE WHICH RECEIVES INFORMATION THROUGH A SPECIAL CENTRAL UNIT, FROM DETECTORS WHICH CONTROL THE BRAKING SYSTEM. IT PREVENTS THE WHEELS FROM LOCKING WHEN BRAKING. USEFUL ON WET GROUND.
ACCELERATION
VARIATION OF INCREASING SPEED AS A FUNCTION OF TIME. 
ADHESIVE FORCE
A TYRE'S ABILITY TO CONVEY SUCH FORCES TO THE GROUND AS TO PERFECTLY GRIP THE ROAD AND PREVENT SKIDDING. 
AERODYNAMICS
BRANCH OF PHYSICS: THE STUDY OF FORCES GENERATED WHEN A MOVING BODY CUTS THROUGH THE AIR AND RELEVANT EFFECTS. 
AIR FILTER
TO PROLONG THE LIFE OF SUCH COMPONENTS AS PISTONS, CYLINDERS AND RINGS (AS WELL AS CRANKSHAFT BEARINGS AND BIG END BEARINGS), AIRBORNE FOREIGN BODIES SHOULD BE PREVENTED FROM ENTERING THE ENGINE. THIS IS WHY CURRENT MOTORCYCLES ARE PROVIDED WITH EFFECTIVE AIR FILTERS. THIS PART MAY BE MADE OF SYNTHETIC "CELL" SPONGE, TREATED PAPER OR, LESS FREQUENTLY, SPECIAL FABRIC; THE LATTER TWO TYPES OF FILTERING ELEMENTS WORK IN DRY CONDITIONS. AIR FILTERS ARE GENERALLY HOUSED IN SPECIAL BOXES, WHICH ALSO WORK AS EXPANSION BOXES AND EXHAUST SILENCERS. 
AIR-BOX
AIR INTAKE UNIT, USED IN A LARGE NUMBER OF MODERN MOTORCYCLES. THE BOX THROUGH WHICH THE CARBURETTORS INTAKE AIR.
ALTERNATOR
ELECTRIC DEVICE WHICH TURNS MECHANICAL ENERGY INTO ALTERNATED CURRENT. IN MOTORCYCLING, IT IS USED AS A POWER GENERATOR.  
BALANCE WEIGHT
BALANCING MASS ECCENTRICALLY PLACED AT A GIVEN DISTANCE FROM THE AXIS OF ROTATION.
BALANCING
IT IS THE OPERATION (OR SEQUENCE OF OPERATIONS) REQUIRED TO BALANCE A ROTATING GEAR (SHAFT, FLYWHEEL, WHEEL, ETC.)
BATTERY
THE "TANK" WHICH STORES ELECTRIC ENERGY IN THE FORM OF DIRECT CURRENT. 
BEARING
TERM REFERRING TO ALL PLAIN BEARINGS. DEPENDING ON THEIR GEOMETRY, BEARINGS CAN BE RING, HALF-SHELL, FLANGED OR THRUST BEARINGS.
BEARING
MECHANICAL COMPONENT LOCATED IN BETWEEN A ROTATING SHAFT AND ITS SUPPORT OR A FIXED AXIS AND A ROTARY ELEMENT. THE BEARING IS USED TO MINIMISE FRICTION AND WEAR.
BEVEL GEAR PAIR
REFERRS TO TWO CONE-SHAPED GEARS, DIRECTLY ENGAGED TO EACH OTHER. BEVEL GEAR PAIRS ARE USED IN END SHAFT DRIVES, TO CHANGE THE DIRECTION OF MOTION BY 90 DEGREES AND PROVIDE FURTHER REDUCTION OF THE REVOLVING SPEED. 
BLOW-BY
GAS PASSING BETWEEN THE PISTON RINGS AND CYLINDER WALL.
BORE
THE INTERNAL DIAMETER OF THE CYLINDER LINER. IT IS EXPRESSED IN MILLIMETRES.
BOXER
IT REFERS TO OPPOSED-CYLINDER ENGINES.
BRAKING FACE
THE PART OF THE DISK (OR DRUM) ON WHICH THE FRICTION MATERIAL OF THE PADS (OR SHOES) WORKS.
BUSHING
A SIMPLE MECHANICAL COMPONENT, HOLLOW INSIDE AND WITH A CYLINDRICAL SHAPE.
BY-PASS
A SYSTEM WHICH LETS A FLUID RUN AROUND SOME SPECIFIC COMPONENTS OR EVEN ENTIRE CIRCUITS. AN EXAMPLE MAY BE THE VALVE WHICH PREVENTS OIL FROM PASSING THROUGH THE RADIATOR UNTIL ITS TEMPERATURE REACHES A GIVEN VALUE.
CAM
ITS MOTION OF ROTATION DETERMINES THE RECTILINEAR DISPLACEMENT OF ANOTHER COMPONENT RESTING AGAINST IT.
CAMSHAFT
IN FOUR-STROKE ENGINES THE ECCENTRICS OF THE CAMSHAFT, WHICH OPERATE TAPPETS OR ROCKER ARMS, CONTROL THE VALVES.
CARBON
NON-METALLIC CHEMICAL ELEMENT NATURALLY EXISTING IN TWO MAIN FORMS: DIAMOND AND GRAPHITE. THE BRAKE DISKS OF GRAND-PRIX MOTORCYCLES ARE MADE OF CARBON AND ARE MATCHED TO CARBON PADS.
CARBURETTOR
INTERNAL DEVICE, SUPPLYING THE ENGINE WITH A PROPER AMOUNT OF AIR-PETROL MIXTURE AND ALLOWING THE DRIVER TO ADJUST POWER OUTPUT.
CATALYST
SUBSTANCE OR ELEMENT WHICH CAN BOOST A CHEMICAL REACTION. IN SOME MOTORCYCLES, TO REDUCE THE AMOUNT OF POLLUTANTS EMITTED BY THE EXHAUST, THE BURNT GASES UNDERGO AN AFTER-TREATMENT, USING CATALYSING PARTICLES INSIDE THE SILENCER (CATALYTIC CONVERTER).
CHAIN
A ROLL CHAIN IS A DRIVING GEAR, CONSISTING OF A SERIES OF LINKS FASTENED TO EACH OTHER BY PIN AND BUSHING JOINTS. THE TEETH OF THE CHAIN WORK ON ROLLS WHICH ARE INSTALLED AROUND THE BUSHINGS.
COIL
A DEVICE GENERATING HIGH-VOLTAGE INDUCED CURRENT, WHICH IS SENT TO THE SPARK PLUG TO IGNITE THE COMBUSTION CHAMBER.
COMBUSTION
IN MOTORCYCLE ENGINES, IT TAKES PLACE FOLLOWING THE IGNITION OF AN AIR-FUEL MIXTURE, WHICH HAS BEEN PREVIOUSLY TAKEN IN AND COMPRESSED INSIDE THE CYLINDER.
COMBUSTION CHAMBER
SPACE WHERE THE GASES CONTAINED IN THE CYLINDER ARE CONFINED AS SOON AS REACHING THE TDC. THE GEOMETRY OF THE CHAMBER IS VERY IMPORTANT FOR THERMAL EFFICIENCY AND COMPRESSION RATIO.
COMPRESSION
THE WORKING PHASE OF AN ENGINE, WHEN THE AIR-FUEL MIXTURE TAKEN INTO THE CYLINDER IS SUBJECTED TO HIGH PRESSURE AND TEMPERATURE.
COMPRESSION RELEASE VALVE
IT SLIGHTLY LIFTS THE EXHAUST VALVE AND LETS OUT PART OF THE CHARGE AT THE END OF THE COMPRESSION STROKE, FACILITATING THE KICK STARTING PROCEDURE.
CONNECTING ROD
IT CONNECTS THE PISTON TO THE CRANKSHAFT.
CONNECTING ROD
MECHANICAL COMPONENT, CONNECTING THE PISTON TO THE CRANK PIN OF THE DRIVING (CRANK) SHAFT.
CONNECTING ROD CAP
IT IS THE REMOVABLE END CAP OF THE CONNECTING ROD.
CONVEYOR
ELEMENT USED TO PROPERLY CONVEY AIR OR LIQUID FLOW. GENERALLY MADE OF PLASTIC OR METAL. ONE OF THE MOST COMMON CONVEYORS IS THE ONE USED AROUND THE HEAT UNIT, IN A LARGE NUMBER OF SCOOTERS.
COUNTER BALANCE SHAFT
DEVICE USED TO REDUCE THE VIBRATIONS WHICH ARE INEVITABLY GENERATED IN A LARGE NUMBER OF ENGINES DUE TO THEIR OWN ARCHITECTURE. IT GENERALLY CONSISTS OF AN ADDITIONAL SHAFT (THOUGH SOMETIMES TWO MAY BE USED) WITH AN ECCENTRIC MASS, THOUGH SOMETIMES A DIFFERENT DEVICE MAY BE USED (SUCH AS AN ADDITIONAL, SUITABLY DRIVEN, CONNECTING ROD). 
COUNTERSHAFT
SOMETIMES REFERRED TO AN ADDITIONAL SHAFT USED AS A DYNAMIC EQUALISER.
CRADLE
A PART WHICH HOUSES AND SUPPORTS THE MOTOR, IN A LARGE NUMBER OF CHASSIS.
CRANK CHAMBER
THE SPACE WITHIN THE BLOCK WHICH ACCOMMODATES THE CRANKSHAFT. ALONG WITH THE LOWER AREA OF THE CYLINDER AND PISTON, IT REPLACES THE PUMP-CRANKCASE, IN WHICH RUNS THE AIR-PETROL MIXTURE SUPPLIED BY THE CARBURETTOR.
CRANKCASE
METAL BOX WHICH ACCOMMODATES, PROTECTS AND SOMETIMES HOLDS MECHANICAL GEARS.
CRANKSHAFT
ALONG WITH THE CONNECTING RODS, IT TURNS THE MOTION OF ROTATION INTO A RECIPROCATING RECTILINEAR MOTION, WHICH IS CONVEYED BY THE PISTONS.
CROWN GEAR
THE LARGER OF TWO GEAR WHEELS DIRECTLY ENGAGED TO EACH OTHER IS CALLED THE CROWN GEAR. THE OTHER IS CALLED "PINION". 
CX
IT IS THE AERODYNAMIC COEFFICIENT OF A BODY. THE LOWER THE CX NUMBER THE LOWER THE AERODYNAMIC DRAG
CYLINDER
THE SPACE WHICH ACCOMMODATES THE PISTON. IF IT IS AN AIR-COOLED ENGINE, THE CYLINDER IS EXTERNALLY FITTED WITH FINS, WHICH INCREASE ITS COOLING CAPACITY. IF IT'S A WATER-COOLED ENGINE, GAPS ARE MADE IN THE CYLINDER WALLS TO LET COOLANT RUN THROUGH. IN MOTORCYCLE ENGINES, CYLINDERS CAN BE REMOVED, I.E. ARE FASTENED TO THE ENGINE BLOCK BY STUD BOLTS AND NUTS.
DAMPER
HYDRAULIC DEVICE USED TO DAMPEN EXCESSIVE MOTION OF SUSPENSION OR STEERING COMPONENTS.
DEAERATION
PROCESS THROUGH WHICH AIR IS REMOVED FROM A LIQUID RUNNING IN A CIRCUIT. ALSO KNOWN AS "BLEEDING". IT IS, FOR INSTANCE, ABSOLUTELY ESSENTIAL TO REMOVE AIR BUBBLES FROM BRAKING FLUID.
DELTABOX
TERM USED BY YAMAHA FOR SOME CHASSIS WITH TWO UPPER LOAD-BEARING BEAMS AND FORKS MADE OF BOX-TYPE, WELDED PLATE.
DESMO VALVE GEAR
MUSHROOM VALVES ARE GENERALLY BROUGHT BACK BY SPIRAL SPRINGS. IN POSITIVE VALVE GEARS, THERE ARE NO SPRINGS TO BRING BACK THE VALVES, SINCE THE LATTER ARE "POSITIVELY" CONTROLLED (I.E. BY A RIGID, GENERALLY CAM-TYPE, MECHANISM). USING A POSITIVE GEAR PROVIDES GREAT ACCURACY IN THE CONTROL OF VALVES' OPERATIONS (THEY MAY BE OPENED AND CLOSED EXTREMELY QUICKLY) AND REMOVES ANY DANGER OF VELVES' "FLOATING" IN THE EVENT OF A RUNAWAY SPEED RATE. 
DETONATION
IT IS AN EXPLOSIVE-TYPE COMBUSTION. A DETONATION OCCURS WHEN CRITICAL PRESSURE AND TEMPERATURE VALUES ARE EXCEEDED. IT MAY BE CAUSED BY AN EXCESSIVELY HIGH COMPRESSION RATIO OR USE OF FUEL WITH EXCESSIVELY LOW OCTANE RATING (FOR THAT TYPE OF ENGINE), OR EVEN SPARK ADVANCE. WHEN IT OCCURS AT MEDIUM-LOW RUNNING, IT OFTEN GIVES RISE TO THE SO-CALLED "ENGINE KNOCK". IF THE DETONATION IS VERY INTENSE, THE ENGINE MAY BE DRASTICALLY DAMAGED. 
DIAL GAUGE
INSTRUMENT USED TO MEASURE THE BORE OF CYLINDERS, INTERNAL DIAMETERS OF HOLES, BEARING HOUSINGS, ETC.
DIFFERENTIAL
IT IS A CLUSTER OF GEARS THAT TRANSMITS TRANSMISSION FORCES TO THE DRIVE AXLE.
DIN
DEUTSCHER INSTITUT FUR NURMUNG. GERMAN STANDARDISATION INSTITUTE. RULES CONCERNING TESTING METHODS FOR THE IDENTIFICATION OF SPECIFIC POWER, TORQUE AND CONSUMPTION OF ENGINES ARE A PARTICULAR CONCERN FOR OUR INDUSTRY. 
DIODE
SEMICONDUCTOR WORKING AS ONE-WAY VALVE. DIODES ARE LARGELY USED INSIDE POWER RECTIFIERS.
DISPLACEMENT
THE VOLUME GENERATED BY A PISTON AS IT DISPLACES FROM ONE DEAD CENTRE TO THE OTHER. IT IS EXPRESSED IN CUBIC CENTIMETRES.
DOHC
AN ACRONYM MEANING DOUBLE OVERHEAD CAMSHAFT.
DROP CENTER
THE CENTRAL PART OF THE WHEEL RIM.
DRY SUMP
IN FOUR-STROKE ENGINES, A LUBRICATING SYSTEM IN WHICH OIL DOES NOT FALL INTO A PAN LOCATED UNDER THE BLOCK, BUT IS SENT INSTEAD BY A SCAVENGER PUMP TO A TANK, FROM WHERE IT IS SUCKED BY THE DELIVERY PUMP TO LUBRICATE MOBILE GEARS.
DUAL IGNITION
SOME ENGINES ARE PROVIDED WITH TWO SPARKING PLUGS PER CYLINDER. A SOLUTION WHICH MAY BE FAVOURABLE IN SOME CASES (VERY HIGH BORES, SPECIALLY DESIGNED COMBUSTION CHAMBERS, ETC.). IT IS USED TO REDUCE AND LIMIT THERMAL SHOCKS AND MAY BE VERY USEFUL TO REDUCE EXHAUST EMISSIONS. 
ELECTRONIC IGNITION PICK-UP
SENSOR USED IN ELECTRONIC IGNITION SYSTEMS TO DISTRIBUTE THE IGNITION CHARGE
EMULSIFIER
IN SOME CARBURETTORS, THE UPPER SECTION OF THE "TUBE" OF THE MAIN CIRCUIT IS FITTED WITH A BRASS TUBE PROVIDED WITH A SERIES OF RADIAL HOLES (GENERALLY CONSISTING OF THE SAME SPRAY NOZZLE), THROUGH WHICH MORE AIR CAN ENTER VIA SPECIAL DUCTS (GENERALLY PROVIDED WITH HOLES OR GAUGED BUSHINGS, CALLED "BRAKING AIR JETS"). THIS CAN PROVIDE A BETTER ATOMISATION OF PETROL, WHICH, AS IT GETS INTO THE DUCT, MAY MIX MORE EASILY WITH THE AIR WHICH IS SUCKED INTO THE CYLINDER. 
ENGINE BLOCK
THE LOAD-BEARING FRAME OF AN ENGINE, TO WHICH THE REMOVABLE PARTS ARE FASTENED (HEAD, CYLINDER, COVERS). 
ENGINE MANAGEMENT SYSTEM
UNIT WHICH CONTROLS SUCH DEVICES AS IGNITION, INJECTION, ETC.
EP
ADDITIVES CALLED EP ("EXTREME PRESSURE"), WHICH ARE USED TO MAKE SOME LUBRICANTS BEAR EXTREMELY HIGH LOADS. 
EXPANSION
THE WORKING PHASE OF THE ENGINE RUNNING CYCLE. IT FOLLOWS COMBUSTION AND OCCURS DUE TO HIGH GAS PRESSURE, WHICH ACTS ON THE PISTON CROWN AND MOVES THE PISTON FROM THE TDC TO THE BDC, TRANSFERRING MECHANICAL ENERGY (WHICH IS CONVEYED TO THE CRANKSHAFT THROUGH THE CONNECTING ROD). 
EXPANSION CHAMBER
IN TWO-STROKE ENGINES, THE LARGEST PART OF AN EXHAUST SYSTEM.
FADING
LOSS OF EFFICIENCY OF THE BRAKES, DUE TO OVERHEATING.
FAIL-SAFE
CHARACTERISTIC OF DEVICES OR CIRCUITS WHICH CAN KEEP WORKING, EVEN IF TO A LIMITED EXTENT OR LESS EFFICIENTLY, EVEN IN THE EVENT OF FAILURES. SPLIT CIRCUITS, DEVICES PROVIDED WITH "EMERGENCY" FUNCTIONS, ETC., BELONG TO THIS GROUP. 
FINS
IN AIR-COOLED ENGINES, THE CYLINDER HEAD IS COVERED WITH A LARGE NUMBER OF FINS, WHICH INCREASE THE EXTENT OF THE METAL SURFACE EXPOSED TO THE COOLING AIR.
FLANGE
PART OF A COMPONENT (PIPING, SHAFT, CONNECTION, CRANKCASE, ETC.) MADE IN SUCH A WAY AS TO SHOW A WIDE, FLAT RESTING (AND HOLDING) SURFACE, WHICH IS THEN CONNECTED TO ANOTHER SIMILARLY SHAPED COMPONENT. 
FLOATING
A GEAR OR COMPONENT INSTALLED INSIDE ANOTHER ONE (OR BOUND TO IT) IN SUCH A WAY AS TO LET IT MOVE QUITE FREELY. MANY BRAKE CALIPERS (PROVIDED WITH ONE FIXED AND ONE MOBILE PAD) ARE FREE TO MOVE SLIGHTLY WITH RESPECT TO THE SUPPORT, SOME BUSHINGS (INSTALLED WITH SLACK BOTH IN THE SEAT AND ON THE SHAFT), AND SO ON. 
FUEL
COMBUSTIBLE SUBSTANCE WHICH IS MIXED WITH AIR TO FUEL SPARK-IGNITED ENGINES.
FUEL FILTER
TO PREVENT ANY FOREIGN BODY FROM GETTING INTO THE CARBURETTOR ALONG WITH PETROL, SMALL MESH FILTERS ARE GENERALLY PLACED AT THE LEVEL OF THE TANK TAP OR THE FUEL INLET CONNECTION OF THE TANK.
GEAR DRIVE
A SET OF GEAR WHEELS, ENGAGED TO EACH OTHER AND GENERALLY LOCATED ONE ABOVE THE OTHER. MOST COMMONLY USED IN TIMING GEARS.
GEARBOX
DEVICE USED TO CHANGE THE GEAR RATIO BETWEEN ENGINE AND REAR WHEEL. GENERALLY CONSISTING OF TWO PARALLEL SHAFTS BEARING TWO SETS OF GEARS ENGAGED TO EACH OTHER.
HORSEPOWER
ENGINE POWER-MEASUREMENT UNIT.
IGNITION
THE ELECTRIC SPARK PRODUCED BY A SPARKING PLUG WHICH STARTS COMBUSTION BETWEEN AIR AND FUEL WHICH HAS JUST ENTERED THE CYLINDERS.
INDUCTION
IN 4-STROKE ENGINES, THE CYCLE PHASE WHEN THE AIR-PETROL MIXTURE ENTERS THE CYLINDER. IN 2-STROKE ENGINES, THE AIR-PETROL MIXTURE IS SUCKED INTO THE CRANK CHAMBER.
INTAKE CHARGE
THE AIR-PETROL MIXTURE SUPPLIED TO THE CYLINDER.
JACK SHAFT
IN SOME ENGINES, IT OPERATES SUCH DEVICES AS THE POWER GENERATOR OR WATER AND PETROL PUMPS.
LEAF SPRING
KIND OF BENDING SPRING, CONSISTING OF ONE OR MORE LEAVES PLACED ONE ON TOP OF THE OTHER.
LIFT
THE LIFTING OF THE VALVE, I.E. THE DISPLACEMENT OF THE VALVE HEAD FROM ITS SEAT.
LINER
THE INTERNAL PART OF THE CYLINDER, WHERE THE PISTON RUNS.
METERING
IT IS THE AIR/FUEL MIXING RATIO (GENERALLY EXPRESSED AS WEIGHT).
MOLYBDENUM DISULPHIDE
A VERY EFFECTIVE ANTI-SCUFFING SUBSTANCE, USED AS A LUBRICANT FOR THE COATING OF SUCH PARTS AS PISTON SKIRTS. LARGELY USED IN MECHANICS.
NUT
FASTENING ELEMENT PROVIDED WITH THREADED AXIAL HOLE; IT IS GENERALLY HEXAGONAL. AVAILABLE IN DIFFERENT FORMS (CAP, BANDED, SELF-LOCKING, ETC..) 
NUT AND BOLT
A SET COMPOSED OF A THREADED SCREW AND NUT.
OIL FILTER
LUBRICANT REACHING THE INTERNAL GEARS OF THE ENGINE MUST BE FREE OF ANY FOREIGN BODY, OF WHATEVER KIND. TO HOLD BACK MINUSCULE FOREIGN BODIES, SPECIAL FILTERS ARE USED. THE SIMPLEST ONES ARE MESH FILTERS, WHICH CAN ONLY HOLD BACK QUITE COARSE PARTICLES, THEN THERE ARE CARTRIDGE FILTERS WHICH CAN HOLD BACK PARTICLES AS SMALL AS A FEW MICRONS IN DIAMETER, AND FINALLY THERE ARE CENTRIFUGAL FILTERS, WHICH USED TO BE VERY COMMON ONCE, BUT HAVE NOW PRACTICALLY DISAPPEARED. 
POSITIVE
SEE POSITIVE VALVE GEAR.
POWER CURVES
THEY ARE THE ENGINE POWER AND TORQUE CURVES, OBTAINED ON THE BENCH WITH THE THROTTLE WIDE OPEN. THEIR CURVES CLEARLY SHOW THE CHARACTERISTICS OF THE ENGINE.
PRE-RELEASE
IN TWO-STROKE ENGINES, IT IS THE DIFFERENCE BETWEEN THE STARTING POINT OF THE DISCHARGING PHASE AND THE ONE WHERE THE EDGE OF THE PISTON CROWN BEGINS TO UNCOVER THE TRANSFER PORTS.
PRESSURE PLATE
IT IS THE COMPONENT THAT APPLIES PRESSURE TO THE CLUTCH PLATES.
PROP SHAFT
CONVEYS THE GEARBOX OUTGOING MOTION TO THE PAIR OF BEVEL GEARS AT THE REDUCING END. IN SOME MOTORCYCLES, IT REPLACES THE DRIVING CHAIN. 
PUMP PAN
IN TWO-STROKE ENGINES, THE CRANK CHAMBER PLUS THE LOWER SECTION OF THE CYLINDER AND PISTON.
RAM AIR-SYSTEM
TO IMPROVE THE FILLING OF CYLINDERS, I.E. TO OBTAIN HIGH VOLUMETRIC EFFICIENCY, ESPECIALLY IN FAST RUNNING CONDITIONS. THE INTAKE SYSTEM IS PRESSURIZED CREATING A RAM EFFECT FOR PERFORMANCE PURPOSE.
RIVETED JOINT
CONNECTION OF TWO MECHANICAL PARTS BY NAILS OR RIVETS. THE RIVETED JOINT IS USED TO BIND HUBS AND ROTORS MADE OF DIFFERENT MATERIALS.
ROCKER ARM
MECHANICAL COMPONENT WITH ONE, TWO OR THREE ARMS, SWINGING AROUND ONE AXIS OR A BALL-HEADED FULCRUM.
ROD
FIXED OR MOBILE RECTILINEAR MECHANICAL COMPONENT WHICH CAN WORK IN DRIVE OR COMPRESSION.
SHAFT
IN MECHANICS, IT MEANS AN ELONGATED CYLINDRICAL COMPONENT. A SHAFT DOES NOT CONVEY TORQUE.
SWINGING ARM
SWINGING LEVER WITH ONE END ATTACHED TO A FRAME (CHASSIS) AND THE OTHER TO A MOBILE ELEMENT, SUCH AS A WHEEL HUB.
SOCKET SCREW
A SCREW WITH A HEXAGONAL SLOTTED HEAD.
SPARK ADVANCE
THE DISTANCE BETWEEN THE POINT WHERE THE SPARK EXPLODES IN THE SPARKING PLUG ELECTRODES AND THE T.D.C. (TOP DEAD CENTRE).
SPARKING PLUG
A DEVICE, THE SPARK OF WHICH IGNITES THE AIR-PETROL MIXTURE CONTAINED IN THE CYLINDER. FASTENED TO THE HEAD BY A THREADED ROOT. AT ONE END IT IS CONNECTED TO THE IGNITION SYSTEM, AT THE OTHER IT OPENS UP INTO THE COMBUSTION CHAMBER. 
SPLINE
CONNECTING GEAR USED TO FIX GEAR WHEELS, ROTORS, PULLEYS, ETC. ON SHAFTS.
SPLIT PIN
METAL SAFETY OR CHECK DEVICE. CONSISTS OF A SMALL, ROUND-SECTION BAR, FORMED IN SUCH A WAY AS TO MAKE AN EYELET AND A CYLINDRICAL STEM.
STEERING HEAD
THE FRONT TUBULAR ELEMENT OF THE CHASSIS, CONTAINING THE STEERING PIN AND THE TWO BEARINGS AROUND WHICH IT TURNS.
THROTTLED BODY
A GEAR HOUSING THE THROTTLE VALVE, WHICH, IN INJECTION FEEDS, ADJUSTS THE INTAKE OF THE ENGINE.
TIMING
CONSISTS OF OPENING ADVANCES AND CLOSING DELAYS OF THE VALVES (OR PORTS IN TWO-STROKE ENGINES) WITH RESPECT TO DEAD CENTRES. THESE ADVANCES AND DELAYS ARE EXPRESSED AS DEGREES OF ROTATION OF THE CRANKSHAFT. TIMING IS THE PARAMETER WHICH MOST DETERMINES THE CHARACTER OF AN ENGINE. A "FORCED" TIMING (I.E. WITH LARGE ADVANCES AND DELAYS) MAKES THE ENGINE ROTATE HIGHER AND BREATH BETTER UNDER FAST RUNNING CONDITIONS AND DELIVER, THEREFORE, HIGHER POWER. AT THE SAME TIME, IT NARROWS THE FIELD OF APPLICATION (LOSS OF PULL AT MEDIUM AND LOW SPEED). A "QUIET" TIMING IS SUITABLE FOR TOURISTIC OR SMALL-POWER ENGINES, SINCE IT PROVIDES A VERY ELASTIC AND "MELLOW" OUTPUT: POWER OUTPUT IS HOWEVER LOWER.
TIMING SYSTEM
THE ASSEMBLY OF ALL COMPONENTS WHICH CONTROL GAS FLOWS IN AND OUT OF CYLINDERS. IN FOUR-STROKE ENGINES, IT CONSISTS OF MUSHROOM VALVES AND ALL THE COMPONENTS WHICH CONTROL AND CLOSE THEM (CAMSHAFT WITH RELEVANT DRIVING CHAIN OR BELT, ROCKER ARMS OR TAPPETS, SPRINGS, ETC.). IN ENGINES WITH ONLY ONE OVERHEAD CAMSHAFT, THE TIMING SYSTEM IS "SINGLE-CAM"; IF, INSTEAD, THERE ARE TWO CAMSHAFTS, THE TIMING IS "TWIN-CAM". IF THE SHAFT IS LOCATED IN THE ENGINE BLOCK AND THE VALVES ARE IN THE HEAD, THE TIMING IS "RODS AND LEVERS". 
TOOTHED BELT
A BELT WHICH DRIVES TWO OR MORE PARALLEL SHAFTS WITHOUT SLIPPING. CONSISTS OF A SYNTHETIC RUBBER BODY, ONE SIDE OF WHICH IS FITTED WITH A SERIES OF V- OR ROUND EDGED TEETH.
TORQUE
THE PRODUCT OF A FORCE AND ARM. REFERRED TO TORSIONAL STRESS. IT MAY BE INCREASED BY GEARS OR BELT/CHAIN DRIVES.
TORQUE CONVERTOR
DEVICE USED IN AUTOMATIC TRANSMISSION DRIVES OF SOME SCOOTERS AND MOPEDS. THE TORQUE CONVERTER ADJUSTS THE ACTION OF THE TRANSMISSION, DETERMINING THE SHIFTING POINT OF THE TRANSMISSION.
TORSION BAR
KIND OF TORSION-OPERATED SPRING, CONSISTING OF A SMALL-DIAMETER CYLINDRICAL BAR BOUND TO ONE FIXED END AND TO THE MOBILE ELEMENT IN THE POSITION OF A FULCRUM.
TREAD
THE PART OF TYRE WHICH TOUCHES THE GROUND.
TWIN-CAM
AN ENGINE IS SAID TO BE TWIN-CAM WHEN THE HEAD ACCOMMODATES TWO CAMSHAFTS.
TWO STROKES
THE RUNNING CYCLE CONSISTS OF JUST TWO STROKES OF THE PISTON. THE HEAD HAS NO VALVES, ONLY A COMBUSTION CHAMBER. INTAKE OCCURS IN THE CRANK CHAMBER, FROM WHICH THE AIR-PETROL MIXTURE IS THEN SENT TO THE CYLINDER. THE LOWER SECTION OF THE CYLINDER IS PROVIDED WITH A SET OF PORTS (TRANSFER AND EXHAUST PORTS) TO LET GASES IN AND OUT, WHICH ARE OPENED UP OR OBSTRUCTED BY THE PISTON, DEPENDING ON THE CYCLE PHASE. 
V-BELT
A SPECIAL TYPE OF FLEXIBLE BELT, V-SHAPED TO OPERATE IN SHALLOW, PARALLEL-GROOVED PULLEYS.
WET SUMP
IN FOUR-STROKE ENGINES, A LUBRICATING SYSTEM IN WHICH OIL FALLS IN A PAN WHICH IS FASTENED UNDER THE BLOCK OR INTEGRAL TO IT. THERE IS ONLY ONE DELIVERY PUMP, AND OIL FALLS BY GRAVITY ALONE.
WISHBONE
IN SOME MOTORCYCLES, AN ELEMENT OF THE SUSPENSION BOUND TO THE CHASSIS BY A SPECIAL FULCRUM AND THE WHEEL.
