How to describe your motorbike parts…

If you are unsure how to describe the motorbike parts you need then this page may help. We have listed some common motorbike parts using our preferred names (which the breakers are familiar with), along with some alternatives and a short description. Click on the categories in the table below to navigate to the relevant section:

CYLINDER HEAD (back to top)
cylinder head (two stroke) [ head ]
In a two stroke engine this is a solid piece of metal which covers the top of the barrel & contains a threaded hole for the spark plug
cylinder head (four stroke) [ head ]
In a four stroke engine the cylinder head is a major engine component containing the valves & camshaft(s). Can be supplied as a bare casting with matching cam caps (& usually the valves) or as a complete assembly including the camshafts. Always specify exactly what you require when ordering. V-twin & V-four engines have two cylinder heads - remember to specify which head you need when ordering i.e. RH / LH for longitudinal crankshaft bikes (e.g. Moto Guzzi 1100 California 750 Breva Griso) or front / rear for transverse crankshaft bikes (e.g. Ducati 900SS Monster 600 620 750 900 / Suzuki TL1000S TL1000R)
camshaft [ cam / cams ]
Shaft with machined ‘pear-shaped’ profiles (lobes). The shape of the cam profiles determines the timing and duration of valve opening within the cylinder head. Engines can use a single camshaft above (SOHC = single overhead cam) or below (OHV = overhead valve) the cylinder head, or twin camshafts (DOHC = double overhead cam)
inlet camshaft [ inlet cam ]
Determines the timing and duration of the inlet valves opening within the cylinder head (DOHC engines)
exhaust camshaft [ exhaust cam / outlet cam ]
Determines the timing and duration of the exhaust valves opening within the cylinder head (DOHC engines)
cam caps Secures the camshaft(s) to the cylinder head. Can be a set of individual caps, or a larger single camshaft retaining plate. Either way, the cam caps are usually cast with the cylinder head and then machined off, so ideally they should be sold with a matching cylinder head
valves [ cylinder head valves ]
Remember to specify if you need a full set or individual inlet & exhaust valves
rockers [ rocker arm ]
Operated by a camshaft, the rocker pivots to push open a valve or valves within the cylinder head
cam bucket [ cam lifters ]
Bucket-shaped component situated between a camshaft profile and a valve
ELECTRICAL & IGNITION (1) (back to top)
CDI unit (carburettor bike) [ spark unit / black box / igniter unit / IC igniter / TR igniter / digital igniter ]
This is the ‘brain’ of an electronic ignition system. It receives engine speed information (usually from a pick-up sensor) and determines when to ignite the fuel mixture. The term ‘CDI’ (Capacitor Discharge Ignition) is a good catch-all term as it is widely used by the breakers, even for igniter units that use transistors rather than capacitors (e.g. XTZ750 Super Tenere / XJ900 58L)
ECU (fuel injection bike) [ Electronic Control Unit / electronic brain / black box / ECM ]
More sophisticated than a CDI unit (which only determines ignition timing), the ECU controls all the bike’s electrical systems (gathering information from various sensors); manages fuel/air mixture and ignition timing etc (e.g. Kawasaki ZX12R)
crank sensor [ crank speed sensor ]
Reports rotational speed of the crankshaft to the ECU to determine ignition timing (similar to a pick-up on a CDI-carburettor bike). Can also double as an engine speed sensor (i.e. revs per minute)
camshaft sensor [ cam sensor ]
Reports camshaft position to the ECU to determine ignition timing (similar to a pick-up on a CDI-carburettor bike)
ELECTRICAL & IGNITION (2) (back to top)
Hall switch [ Hall effect sensor ]
Found on fuel injection bikes with latest CAN-BUS type ECU systems (e.g. BMW). The Hall switch is often used as an ignition trigger and/or crankshaft sensor reporting a digital signal to the engine’s ECU to determine ignition timing
MAP sensor [ Air map sensor / Manifold Absolute Pressure sensor ]
Provides manifold pressure information to the ECU in order to determine the correct fuel flow
Lambda sensor [ O2 / oxygen sensor ]
Determines whether the air fuel ratio exiting the combustion chamber is rich (unburnt fuel vapour) or lean (excess oxygen)
STV sensor Secondary Throttle Valve sensor. On bikes with dual butterfly throttle bodies (e.g. Suzuki GSXR75)
Coolant temperature sensor Reports coolant temperature to ECU
tilt sensor [ bank sensor / lean angle sensor ]
Cuts fuel injection if bike is horizontal (i.e. as a safety feature in the avent of an accident)
HT coil (s) [ ignition coil (s) / High Tension coils ]
Transforms the 12 volts from the battery to a higher voltage necessary for the spark plugs to create a spark. Although commonly termed ‘ignition coil’ there are other coils involved in the ignition system (e.g. stator coils, pick-up coils), so it is best to use the term HT coil
ELECTRICAL & IGNITION (3) (back to top)
knock sensor Detects detonation inside the combustion chamber outside the normal combustion cycle. If detonation occurs the ECU usually retards the ignition timing to prevent the collision of different combustion fronts which could potentially damage the engine
stick coils [ coil-on-plug / direct ignition coils ]
When the HT coils are incorporated into the spark plug caps rather than being remotely positioned
generator [ alternator ]
Converts mechanical energy (i.e. from the engine’s crankshaft) into alternating electrical current by utilising a rotating magnetic field. Generators have two main components; the flywheel (rotor) which contains magnets, and the stator which contains copper wire (windings). The flywheel rotates around the stator to generate alternating current
stator [ stator plate / generator windings / alternator windings ]
Main component of the bike’s generator comprising copper wire wound around a support frame. The stator remains stationary whilst the flywheel rotates around it
flywheel [ rotor / generator rotor / alternator rotor ]
Main component of the bike’s generator containing magnets. The flywheel rotates around the stator producing a magnetic field which generates alternating electrical current (e.g. Kawasaki GPZ500 S EX500 A D)
ELECTRICAL & IGNITION (4) (back to top)
pick-up coils [ pulser coil / pulsar coil / signal generator ]
Detects the crankshaft speed from the generator flywheel or a separate timing rotor and sends an electrical signal to the bike’s CDI unit (which alters the ignition timing accordingly)
points system Mechanical ignition timing system (e.g. early Honda CG125)
points [ contact breakers ]
Opens & breaks the electrical circuit that sends current to the HT coil(s) in order to initiate a spark
points condensor Acts as a ‘mini-battery’ by storing electrical charge between ignition cycles; component part of points ignition systems
points cam [ points camshaft ]
Small profiled camshaft which open & closes the points contacts on mechanical ignition systems
points plate Metal plate mounting the points, points cam & condenser on mechanical ignition systems
ATU [ Automatic Timing Unit / advance-retard unit ]
Found on mechanical (points) & early semi-electronic ignition systems (e.g. Kawasaki GPz550 H KZ550H). The ATU changes the profile of the points cam which alters the ignition timing. Usually operates by centrifugal force driven by the rotational speed of the crankshaft
ELECTRICAL & IGNITION (5) (back to top)
regulator [ voltage regulator ]
Electrical component designed to maintain a constant voltage level
rectifier Converts alternating current (AC) produced by the generator / alternator to direct current (DC) used by the bike’s electrical systems & stored in the battery
regulator-rectifier [ reg rec ]
Combines regulator & rectifier functions into a single electrical unit (e.g. Honda VFR750F / CBR600 F)
fuse box [ fuse holder / fusebox ]
Contains the main fuses for the bike’s electrical systems
battery Usually 12 volt on modern bikes (e.g. Honda C90 Cub), but some early bikes had 6 volt electrics (e.g. Honda C90 ZZ)
relay Electrical switch with a higher power output circuit than its input circuit. Controls a high current circuit with a low current signal (e.g. starter relay)
starter relay [ starter solenoid ]
Converts the low current signal sent by the ignition switch to a higher current necessary to power the starter motor
ELECTRICAL & IGNITION (6) (back to top)
diode Electrical component allowing current to pass in one direction only (blocking it in the opposite direction) - often used to stop current passing from one electrical circuit to another
resistor Electrical component designed to restrict the flow of electrical current. The amount of resistance (measured in ohms) can be a fixed value or variable (a potentiometer)
horn [ horns ]
ENGINE (1) (back to top)
engine [ motor / lump ]
Can be supplied ‘complete’, stripped bare (basic engine), or pretty much anywhere in between! Most breakers remove at least some ‘ancillary’ parts from an engine and sell them separately (which is fair enough - you wouldn’t want to buy a complete engine if you only needed a starter motor). So, if you ask for a ‘complete engine’ it may or may not include the starter motor, outer engine covers, generator or clutch etc. It is always worth double-checking exactly what you are getting for the price quoted
complete engine & running gear Generally accepted to mean the engine + everything required to make it run - e.g. for a car project. Should include CDI / ECU, carbs / injectors, wiring loom, generator, clutch etc, but can vary from model to model - some fuel injected bikes may also need the clocks and/or ignition switch & master key (for immobiliser) to make the engine run
bottom end [ short engine / bottom half ]
The engine without the barrels (unless part of the upper crank case) and cylinder head. Includes the main crankcases, crankshaft & gearbox. You need to check whether the generator, clutch & outer engine covers are included or not
ENGINE (2) (back to top)
barrel / barrels [ cylinders ]
Part of the engine which the pistons(s) travel up & down inside. Some modern bikes incorporate the barrels in the same casting as the upper crankcase. V-four & V-twin bikes have two separate sets of barrels - If you don’t need both, remember to specify which you need when ordering (i.e. front /rear, RH / LH)
crankshaft [ crank ]
Steel shaft in the bottom of the engine which translates the linear motion of the piston/s into rotation. The piston/s connect to the crankshaft by connecting rods (con rods). Often sold as a set, i.e. crank & rods
crank cases [ crankcases ]
Main structural part of the engine encasing the crankshaft and gearbox. Crank cases can be split horizontally (i.e. top & bottom) or vertically (RH & LH) and are machined from the same casting so should really be sold as a matching pair. Not to be confused with the outer engine covers
pistons Often sold as a matching set with the barrel(s) i.e. barrel, piston & rings
pushrod (OHV engines) Situated between the camshaft (in the bottom end of the engine) and cylinder head rocker (top of the engine). The camshaft profile moves the pushrod upwards to engage the rocker which in turn opens a valve in the head
water jacket Situated above cylinder head on some two stroke bikes (e.g. Honda MTX125). Seals the coolant flowing over the top of the barrel
starter motor [ electric starter / starting motor ]
Electric motor used to turn the engine over when starting the bike / scooter (e.g. Cagiva River 500 Canyon 600 / Honda CBX750)
starter gears [ starter clutch ]
Mechanism (usually a series of gears) allowing the the starter motor to turn the engine (e.g. Aprilia SL1000 Falco / Tuono 1000 / RSV Mille)
kickstart mechanism Mechanism (usually gears) allowing the kickstart lever/shaft to turn the engine (e.g. Suzuki RM250 DR350 S / Kawasaki KX250 / Honda CR250 / Yamaha WR250)
balance shaft An eccentric weighted shaft used to reduce engine vibration & other stresses (e.g. Yamaha TDM850 TDM900 TRX850)
cam chain [ camshaft chain ]
Chain providing drive to the camshaft(s) via the crankshaft
cam chain tensioner [ camshaft chain adjuster ]
Located on the rear of the cylinder head. Usually contains a spring & ratchet mechanism which pushes a plunger to tension the cam chain
cam chain guide / guides Guides for the cam chain, often situated at the front & rear inside the cylinder head
cam belt [ camshaft belt ]
Belt providing drive to the camshaft (s) via the crankshaft (e.g. Ducati 748 848 916 996 998 1098)
cam belt guide Guides for the cambelt
cam belt tensioner [ camshaft belt adjuster ]
cam gears [ cam drive gears ]
Linked set of gears providing drive from the crankshaft to the camshafts (e.g. Honda VFR750)
oil pump (4 stroke engines) Mechanical pump circulating oil around the engine
oil pump (2 stroke engines) Mechanical pump delivering 2 stroke oil to the inlet manifold / cylinder barrel
ENGINE COVERS (back to top)
points cover Covers the contact breakers / points assembly on mechanical ignition bikes (i.e. pre-electronic ignition)
clutch cover Large engine cover over the clutch assembly, usually (but not always) on the RHS of the engine. On engines with a wet clutch the cover often has a oil-slight glass / dipstick and aperture to replace / top up the engine oil
front sprocket cover (chain drive) Cover over the front drive sprocket, usually (but not always) on the LHS of the engine
transmission cover (chain drive) [ gearbox cover ]
Located behind the front sprocket (e.g. Kawasaki ZZ-R1100)
transmission cover (scooter/moped) Covers the variator & clutch assembly, usually on the LH side of the engine
pick-up cover [ timing cover / pulsar cover / ignition cover ]
Small engine cover over the pick-up assembly (signal generator / pulser); usually on the RHS of the engine
water pump cover [ water pump casing / impellor cover ]
cam cover [ rocker cover / cylinder head cover ]
cam cover [ rocker cover / cylinder head cover ]
sump [ sump pan / sump plate ]
Cover underneath the engine where oil pools when the bike is not in use. Usually contains the oil drain plug
EXHAUST (back to top)
complete exhaust system Full system including all component parts (downpipes, silencers, collector etc)
downpipes [ headers / header pipes / exhaust manifold (4 stroke) / front pipe /s (2 stroke) ] Front part of exhaust system that mounts to the cylinder head (on 4 stroke engines) or cylinder barrel (on 2 stroke engines). Can be one complete welded unit, or individual pipes
collector box Joins separate downpipes together & then attaches to the silencers (usually twin silencer bikes)
link pipe [ intermediate pipe / connector pipe ]
Joins downpipes to silencer (usually single silencer bikes). As original equipment it is often welded to silencer as one unit, but aftermarket performance cans usually have separate link pipes
silencer / silencers [ muffler / end can ]
Rear section of the exhaust containing the baffles / packing to reduce noise
race can Performance silencer, often without baffles or with removable baffles
exhaust downpipe valve [ EXUP valve (Yamaha) / HTEV / HVIX valve (Honda) / EXCV (Suzuki) ]
Flap / valve assembly situated in the exhaust manifold. Designed to increase mid-range engine power by altering exhaust gas back-pressure. Progressively opens (hi revs) or closes (low revs) depending on engine speed. Not to be confused with an exhaust valve in the cylinder head of four stroke engines!
exhaust valve servo motor [ exhaust valve actuator / EXUP / HVIX / EXCV motor ]
Small electric motor which opens & closes the valve in the exhaust downpipes. May also control a flap in the airbox to change air pressure / flow
exhaust heat shield Usually on silencer - protects rider from exhaust heat
catalytic converter Unit containing precious metals to reduce exhaust gas emissions. Often incorporated into the silencer assembly
BELT DRIVE (back to top)
drive belt [ final drive belt ]
A toothed belt which transmits drive from the front drive pulley to the rear drive pully (e.g. Harley Davidson 883 Sportster 1200)
rear drive pully [ rear pulley ]
Connects to rear wheel & drive belt (e.g. Kawasaki GPz305 / EN500)
front drive pulley [ front pulley ]
Connects to gearbox output shaft & drive belt (e.g. BMW F650 CS Scarver)
CHAIN DRIVE (back to top)
chain & sprocket set [ chain & sprockets ]
Comprises the drive chain, front & rear sprockets. Ideally all should be changed together so they wear at the same rate
rear sprocket carrier Holds rear drive sprocket & has lugs that slot into the rear wheel
cush drive rubbers Fits between the lugs on the sprocket carrier & the rear wheel. Provides a cushion between the wheel & rear sprocket during acceleration & engine braking

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