BTEB Motorcycle Servicing flashcards

32 cards. Read the term and the definition here. The deck at the top of this page is optional.

Carbon monoxide hazard

An odourless, colourless gas in exhaust that binds haemoglobin far more strongly than oxygen. Engines must never run in a closed workshop bay without forced ventilation.

Petrol fire extinguisher class

Petrol is a Class B flammable liquid, extinguished with foam, dry powder, or carbon dioxide. Water spreads burning fuel and must never be used on a petrol fire.

Torque formula

Torque equals force multiplied by perpendicular distance from the pivot. A 150 newton force applied at 0.3 metre gives 45 newton metres of tightening torque.

Torque wrench storage

A torque wrench is a measuring instrument. It is stored at its lowest scale setting, never used to loosen fasteners, and recalibrated after being dropped.

Vernier calliper least count

The smallest value a vernier calliper can read, equal to main scale division divided by number of vernier divisions. A 1 mm main scale with 50 divisions reads 0.02 mm.

Micrometer least count

Screw pitch divided by thimble divisions. A 0.5 mm pitch screw with a 50-division thimble resolves 0.01 mm, read on the sleeve and thimble scales.

Plastigauge use

A crushable plastic strip placed across the bearing journal. After tightening, its flattened width compared with the printed scale gives bearing oil clearance.

Four-stroke cycle

Intake, compression, power, and exhaust strokes, completed in two crankshaft revolutions or 720 degrees, producing one power stroke per cylinder.

Compression ratio formula

Swept volume plus clearance volume, divided by clearance volume. A 150 cc cylinder with 15 cc clearance volume gives a ratio of 11 to 1.

Swept volume formula

Cylinder volume equals pi divided by four, multiplied by bore squared and stroke. Total engine displacement is this value times the number of cylinders.

Engine detonation cause

Spontaneous ignition of unburnt end gas after the spark, producing knock. Causes include low octane fuel, excessive compression, lean mixture, and hot spots.

Valve clearance setting

The gap between valve stem and rocker or cam, set cold on most air-cooled engines. Too little clearance causes hard starting, compression loss, and burnt valves.

Leak-down test meaning

Air escaping at the exhaust port indicates a leaking exhaust valve, at the intake port an intake valve, and at the oil filler worn rings or piston.

Head bolt torque pattern

Fasteners are tightened in a spiral or cross sequence in two or three increasing stages to the specified figure, using clean threads and a new gasket.

Stoichiometric air-fuel ratio

The chemically ideal petrol-air mass ratio of about 14.7 to 1. Richer mixtures cool combustion; leaner mixtures raise temperature and detonation risk.

Carburettor pilot circuit

The fuel and air passage controlling mixture at idle and just off idle, adjusted by the pilot screw, with the throttle slide almost closed.

Spark plug heat range

A rating of how quickly a plug sheds heat. A hot plug suits low-load engines; a cold plug suits sustained high speed to avoid pre-ignition.

Oil viscosity grade meaning

In a grade such as 10W-40, the first number describes low-temperature pumping behaviour and the second the viscosity at 100 degrees Celsius.

Overall drive ratio

Primary reduction multiplied by gearbox ratio and final drive ratio. It relates engine speed to wheel speed; a lower numeric ratio allows higher road speed.

Clutch lever free play

The small gap before the clutch begins to disengage, typically 10 to 20 mm at the lever. Zero free play causes slip and rapid friction plate wear.

Chain slack measurement

Free movement measured at the midpoint of the lower chain run, usually 20 to 30 mm. Too tight a chain overloads countershaft and wheel bearings.

Pascal's law in brakes

Pressure applied to a confined fluid is transmitted equally in all directions, so a small master-cylinder piston force produces large calliper clamping force.

Spongy brake lever cause

Air or moisture in the hydraulic circuit compresses under pressure. The circuit is bled at the calliper nipple until lever feel becomes firm.

Suspension sag setting

The difference between fully extended and rider-loaded suspension length. It sets ride height and must be correct before damping adjustments are judged.

Ohm's law

Voltage equals current multiplied by resistance. A 12 volt circuit drawing 4 amperes has 3 ohms resistance and dissipates 48 watts of power.

Series and parallel circuits

In series, current is common and voltages add. In parallel, voltage is common and currents add, which is how motorcycle electrical loads are wired.

Battery open-circuit voltage

A fully charged 12 volt lead-acid battery reads about 12.6 volts at rest, since each of six cells produces roughly 2.1 volts.

Charging voltage check

With the engine at mid speed, battery voltage should rise to roughly 13.5 to 14.5 volts. Lower readings suggest a faulty regulator, rectifier, or stator.

Voltage drop test

Measuring voltage lost across a connection while the circuit is loaded. A drop above about 0.5 volts indicates corrosion, looseness, or a poor earth.

Pre-ride safety check

A quick inspection before riding covering tyre pressure and condition, brake operation, lights, horn, oil and fuel levels, and drive chain or belt tension.

Diagnostic troubleshooting order

Confirm the complaint, verify it with a test, isolate the system, then test components from most likely and easiest, and re-verify after repair.

Job card record

A written record of the customer's complaint in their words, the diagnosis, parts fitted, labour hours, and warranty terms for the repair.