# Motorcycle glossary

> 71 definitions of motorcycle parts and maintenance terms.

- [Variator](https://motorsikletparcasi.com/en/glossary/variator): A variator is the pulley system in scooters and other CVT motorcycles that changes the drive ratio steplessly according to engine speed.
- [Variator rollers](https://motorsikletparcasi.com/en/glossary/variator-rollers): Variator rollers are cylindrical weights in the front variator that move outwards under centrifugal force and increase the belt's running diameter.
- [CVT drive belt](https://motorsikletparcasi.com/en/glossary/cvt-drive-belt): A CVT drive belt is the V-section, cogged rubber belt that carries power between the front and rear variator pulleys of a scooter.
- [CVT (continuously variable transmission)](https://motorsikletparcasi.com/en/glossary/cvt): A CVT is the automatic transmission used in scooters that varies the drive ratio continuously with variator pulleys and a belt, without fixed gears.
- [Centrifugal clutch](https://motorsikletparcasi.com/en/glossary/centrifugal-clutch): A centrifugal clutch is the automatic clutch in scooters whose shoes swing out under centrifugal force as revs rise and grip the clutch bell to drive the wheel.
- [Clutch](https://motorsikletparcasi.com/en/glossary/clutch): The clutch connects and disconnects drive between the engine and the gearbox under the rider's control.
- [Clutch plates](https://motorsikletparcasi.com/en/glossary/clutch-plates): Clutch plates are the friction-lined discs in a wet multi-plate clutch that clamp against the steel plates to transmit engine power to the gearbox.
- [Clutch cable](https://motorsikletparcasi.com/en/glossary/clutch-cable): A clutch cable is the sheathed steel cable that links the clutch lever to the clutch release mechanism on the engine.
- [Gearbox](https://motorsikletparcasi.com/en/glossary/gearbox): The gearbox transmits engine speed to the wheel through different ratios so the motorcycle can run efficiently at any speed.
- [Fairing](https://motorsikletparcasi.com/en/glossary/fairing): Fairings are the plastic or composite body panels that enclose a motorcycle's engine and frame for aerodynamics, protection and looks.
- [Carburettor](https://motorsikletparcasi.com/en/glossary/carburettor): A carburettor is the mechanical fuel system component that mixes petrol into the incoming air in the correct proportion.
- [Fuel injector](https://motorsikletparcasi.com/en/glossary/fuel-injector): A fuel injector is the solenoid valve in fuel-injected engines that sprays pressurised fuel into the intake on command from the engine control unit (ECU).
- [Throttle body](https://motorsikletparcasi.com/en/glossary/throttle-body): The throttle body controls how much air enters a fuel-injected engine using a butterfly valve linked to the twist grip.
- [Fuel pump](https://motorsikletparcasi.com/en/glossary/fuel-pump): The fuel pump is the electric pump in fuel-injected motorcycles that delivers fuel from the tank to the injector at constant pressure.
- [Choke](https://motorsikletparcasi.com/en/glossary/choke): The choke enriches the fuel-air mixture (adds more fuel) to help start a cold engine.
- [Idle speed](https://motorsikletparcasi.com/en/glossary/idle-speed): Idle speed is the lowest engine speed at which the engine keeps running with the throttle closed.
- [CDI (capacitor discharge ignition)](https://motorsikletparcasi.com/en/glossary/cdi): A CDI (capacitor discharge ignition) unit stores energy in a capacitor and dumps it into the ignition coil to create the spark at the spark plug.
- [Ignition coil](https://motorsikletparcasi.com/en/glossary/ignition-coil): The ignition coil is a transformer that steps up the low voltage from the CDI or ECU to the many thousands of volts needed to fire the spark plug.
- [Regulator rectifier](https://motorsikletparcasi.com/en/glossary/regulator-rectifier): A regulator rectifier converts the stator's AC output to DC and limits the charging voltage to protect the battery and electrics.
- [Stator](https://motorsikletparcasi.com/en/glossary/stator): The stator is the set of fixed coil windings inside the flywheel that generate alternating current together with the flywheel magnets.
- [Flywheel magneto](https://motorsikletparcasi.com/en/glossary/flywheel-magneto): The flywheel is the heavy rotating disc on the crankshaft that carries magnets; with the stator it generates electricity and smooths engine rotation.
- [Spark plug](https://motorsikletparcasi.com/en/glossary/spark-plug): A spark plug ignites the fuel-air mixture in the cylinder with a spark across its electrodes.
- [Battery](https://motorsikletparcasi.com/en/glossary/battery): A motorcycle battery is the 12-volt lead-acid or lithium battery that turns the starter motor and powers the electrics when the engine is off.
- [Starter motor](https://motorsikletparcasi.com/en/glossary/starter-motor): The starter motor is a small DC electric motor that turns the crankshaft using battery power to start the engine.
- [Starter clutch](https://motorsikletparcasi.com/en/glossary/starter-clutch): The starter clutch is a one-way clutch that passes the starter motor's drive to the crankshaft and freewheels once the engine fires.
- [Brake pad](https://motorsikletparcasi.com/en/glossary/brake-pad): A brake pad is the friction-lined part that the caliper pistons press against the brake disc to slow the motorcycle.
- [Brake disc](https://motorsikletparcasi.com/en/glossary/brake-disc): The brake disc is the steel rotor fixed to the wheel that the brake pads clamp to slow the motorcycle.
- [Brake caliper](https://motorsikletparcasi.com/en/glossary/brake-caliper): A brake caliper uses hydraulic pressure to move its pistons and press the brake pads onto the disc.
- [Brake master cylinder](https://motorsikletparcasi.com/en/glossary/brake-master-cylinder): The brake master cylinder converts force on the brake lever or pedal into hydraulic pressure and sends it to the caliper.
- [Brake fluid](https://motorsikletparcasi.com/en/glossary/brake-fluid): Brake fluid is the high-boiling-point fluid that carries pressure from the master cylinder to the caliper.
- [Drum brake](https://motorsikletparcasi.com/en/glossary/drum-brake): A drum brake works by brake shoes expanding against the inside of a drum in the wheel hub.
- [ABS (anti-lock braking system)](https://motorsikletparcasi.com/en/glossary/abs): ABS (anti-lock braking system) detects a wheel about to lock under hard braking and modulates brake pressure many times a second to keep grip.
- [Shock absorber](https://motorsikletparcasi.com/en/glossary/shock-absorber): A shock absorber combines a spring and a damper to soak up bumps and keep the wheel in contact with the road.
- [Front fork](https://motorsikletparcasi.com/en/glossary/front-fork): The front fork is the twin-tube telescopic assembly that holds the front wheel and provides front suspension with springs and oil.
- [Steering head bearing](https://motorsikletparcasi.com/en/glossary/steering-head-bearing): Steering head bearings are the upper and lower bearings that let the front fork turn smoothly in the frame's steering head.
- [Swingarm](https://motorsikletparcasi.com/en/glossary/swingarm): The swingarm is the rear suspension arm that connects the rear wheel to the frame and pivots up and down with the shock.
- [Chain and sprocket kit](https://motorsikletparcasi.com/en/glossary/chain-and-sprocket-kit): A chain and sprocket kit is the front sprocket, rear sprocket and chain that make up the final drive to the rear wheel.
- [O-ring chain](https://motorsikletparcasi.com/en/glossary/o-ring-chain): An O-ring chain has rubber rings between the link plates that seal grease inside the pin and bushing for longer life.
- [Chain slack](https://motorsikletparcasi.com/en/glossary/chain-slack): Chain slack is the total up-and-down movement of the lower chain run measured midway between the sprockets.
- [Final drive ratio](https://motorsikletparcasi.com/en/glossary/final-drive-ratio): The final drive ratio is the rear sprocket tooth count divided by the front sprocket tooth count; it sets how engine power is geared to the wheel.
- [Bearing](https://motorsikletparcasi.com/en/glossary/bearing): A bearing is a machine element that reduces friction between a rotating shaft and a fixed housing using balls or rollers.
- [Gasket](https://motorsikletparcasi.com/en/glossary/gasket): A gasket is a thin seal between two fixed surfaces that stops oil, coolant, fuel or gas from leaking out of the joint.
- [Oil seal](https://motorsikletparcasi.com/en/glossary/oil-seal): An oil seal is a lipped seal on a rotating or sliding shaft that keeps oil in and dirt out.
- [Piston ring](https://motorsikletparcasi.com/en/glossary/piston-ring): Piston rings sit in grooves on the piston; they seal combustion pressure, scrape oil off the cylinder wall and carry heat to the cylinder.
- [Piston](https://motorsikletparcasi.com/en/glossary/piston): The piston moves up and down in the cylinder and transfers combustion pressure to the crankshaft through the connecting rod.
- [Cylinder](https://motorsikletparcasi.com/en/glossary/cylinder): The cylinder is the part of the engine in which the piston moves and combustion takes place.
- [Cylinder head](https://motorsikletparcasi.com/en/glossary/cylinder-head): The cylinder head closes the top of the combustion chamber and carries the valves, camshaft and spark plug.
- [Crankshaft](https://motorsikletparcasi.com/en/glossary/crankshaft): The crankshaft converts the piston's up-and-down motion into rotation through the connecting rod.
- [Connecting rod](https://motorsikletparcasi.com/en/glossary/connecting-rod): The connecting rod links the piston to the crankshaft and transfers the piston's linear motion into crank rotation.
- [Camshaft](https://motorsikletparcasi.com/en/glossary/camshaft): The camshaft uses its cam lobes to open and close the valves at the right time.
- [Cam chain](https://motorsikletparcasi.com/en/glossary/cam-chain): The cam chain (timing chain) drives the camshaft from the crankshaft and keeps valve timing in sync.
- [Valve](https://motorsikletparcasi.com/en/glossary/valve): A valve is the mushroom-shaped part in the cylinder head that opens and closes the intake and exhaust ports.
- [Valve clearance](https://motorsikletparcasi.com/en/glossary/valve-clearance): Valve clearance adjustment sets the gap between the valve stem and the part that opens it (rocker or bucket) to the value in the manual.
- [Engine oil](https://motorsikletparcasi.com/en/glossary/engine-oil): Engine oil lubricates, cools and cleans the engine's moving parts; on most motorcycles it also lubricates the clutch and gearbox.
- [JASO (MA, MA2, MB)](https://motorsikletparcasi.com/en/glossary/jaso-oil-standard): JASO T903 is the Japanese standard that classifies four-stroke motorcycle oils by their compatibility with wet clutches: MA, MA1, MA2 and MB.
- [Oil filter](https://motorsikletparcasi.com/en/glossary/oil-filter): An oil filter traps metal particles and dirt in the engine oil so that clean oil circulates through the engine.
- [Air filter](https://motorsikletparcasi.com/en/glossary/air-filter): An air filter stops dust and particles in the intake air, protecting the cylinder, piston and rings from wear.
- [Radiator](https://motorsikletparcasi.com/en/glossary/radiator): A radiator is the heat exchanger in liquid-cooled engines that transfers heat from the hot coolant to the air.
- [Water pump](https://motorsikletparcasi.com/en/glossary/water-pump): The water pump circulates coolant between the engine and the radiator in liquid-cooled engines.
- [Tyre size](https://motorsikletparcasi.com/en/glossary/tyre-size): A tyre size is the code giving tread width (mm), aspect ratio (%) and rim diameter (inches), e.g. 120/70-17.
- [Tyre pressure](https://motorsikletparcasi.com/en/glossary/tyre-pressure): Tyre pressure is the air pressure inside the tyre, measured in bar or psi; it directly affects grip, braking distance, tyre life and fuel use.
- [Wheel rim](https://motorsikletparcasi.com/en/glossary/wheel-rim): A wheel rim is the metal hoop the tyre sits on; it is joined to the hub by spokes or cast spokes to form the wheel.
- [Speedometer cable](https://motorsikletparcasi.com/en/glossary/speedometer-cable): A speedometer cable is the flexible sheathed cable that carries rotation from the speedometer drive gear at the wheel hub to a mechanical speedometer.
- [Throttle cable](https://motorsikletparcasi.com/en/glossary/throttle-cable): A throttle cable transmits the twist grip's movement to the carburettor slide or throttle butterfly.
- [Exhaust](https://motorsikletparcasi.com/en/glossary/exhaust): The exhaust system carries burnt gases away from the cylinder and consists of the header (manifold), catalytic converter and silencer.
- [VIN (vehicle identification number)](https://motorsikletparcasi.com/en/glossary/vin): The VIN (vehicle identification number) uniquely identifies a vehicle; on modern vehicles it is a standardised 17-character code.
- [OEM part](https://motorsikletparcasi.com/en/glossary/oem-part): An OEM part is made by the motorcycle manufacturer or on its behalf and matches the part fitted at the factory.
- [Aftermarket part](https://motorsikletparcasi.com/en/glossary/aftermarket-part): An aftermarket part is made by another manufacturer to replace the original part with the same dimensions and function.
- [Engine displacement (cc)](https://motorsikletparcasi.com/en/glossary/engine-displacement): Engine displacement is the total volume swept by the pistons from bottom to top dead centre, expressed in cubic centimetres (cc).
- [Torque](https://motorsikletparcasi.com/en/glossary/torque): Torque is the turning force the engine produces at the crankshaft, measured in newton-metres (Nm).
- [Engine speed (rpm)](https://motorsikletparcasi.com/en/glossary/rpm): Engine speed is the number of crankshaft revolutions per minute (rpm), shown on the tachometer.

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