NABTEB Motor Vehicle Mechanics flashcards
NABTEB Motor Vehicle Mechanics · Build recall with a focused review session.
32 cards. Read the term and the definition here. The deck at the top of this page is optional.
- Fire triangle
- The three elements needed for combustion are fuel, oxygen and heat; removing any one element prevents or extinguishes a fire.
- Class B fire
- A fire involving flammable liquids such as petrol or diesel; extinguish with foam, carbon dioxide or dry powder, never with a water jet.
- Carbon monoxide hazard
- Exhaust gas carbon monoxide is colourless, odourless and poisonous; run engines only in ventilated areas or duct exhaust outdoors to prevent poisoning.
- Micrometer least count
- A metric outside micrometer usually reads to 0.01 mm by combining the barrel scale with the thimble scale; read both scales and add the values.
- Torque wrench use
- A torque wrench tightens fasteners to a specified torque in newton metres; set the value, apply force smoothly and recalibrate it periodically.
- Feeler gauge purpose
- A set of thin metal blades of known thickness used to measure small gaps such as valve clearances, spark plug gaps and piston ring end gaps.
- Four-stroke cycle
- The four piston strokes are intake, compression, power and exhaust; the crankshaft makes two complete revolutions for one complete cycle in a four-stroke engine.
- Engine displacement formula
- Total engine displacement equals pi divided by four, multiplied by bore squared, multiplied by stroke, multiplied by the number of cylinders.
- Compression ratio
- Compression ratio is the total cylinder volume above the piston at bottom dead centre divided by the clearance volume at top dead centre.
- Plastigauge bearing check
- Plastigauge is a plastic strip placed across a bearing journal; tightening the cap flattens it, and its width indicates the bearing clearance.
- Cylinder taper measurement
- Measure cylinder bore at top, middle and bottom in two directions with a bore gauge; taper or out-of-round beyond the service limit requires reboring.
- Torque sequence rule
- Tighten cylinder head bolts in the manufacturer's sequence, usually from the centre outward in stages, to avoid warping the head and gasket leaks.
- Stoichiometric air-fuel ratio
- For petrol, the ideal mass air-fuel ratio is about 14.7 to 1; richer mixtures use more fuel, leaner mixtures use less fuel and may burn hotter.
- Ignition timing advance
- Ignition timing advance fires the spark before top dead centre; excessive advance causes pinging or detonation, while retarded timing reduces power and overheats exhaust.
- Oxygen sensor feedback
- The oxygen sensor measures exhaust oxygen and sends a voltage signal to the engine control unit, which adjusts injection duration to maintain closed-loop mixture control.
- Clutch purpose
- The clutch connects and disconnects engine torque to the gearbox, allowing smooth starts and gear changes by slipping between the flywheel and friction disc.
- Gear ratio calculation
- Gear ratio equals the number of teeth on the driven gear divided by the number on the driving gear; a numerically higher ratio increases torque and reduces speed.
- Differential function
- The differential transfers drive to the wheels through the crown wheel and pinion while allowing the outer wheel to rotate faster than the inner wheel during turns.
- Caster angle effect
- Caster is the tilt of the steering axis from vertical; positive caster improves straight-line stability and steering self-centring but increases steering effort.
- Camber angle
- Camber is the inward or outward lean of the wheel from vertical; incorrect camber causes uneven tyre wear and affects cornering grip.
- Toe setting
- Toe is the difference in distance between the front and rear of the two wheels; toe-in reduces straight-line instability, while excessive toe scrubs tyres.
- Brake fade
- Brake fade is loss of braking force when friction surfaces overheat, commonly from repeated hard braking; cooling and correct lining material reduce the risk.
- Hydraulic brake principle
- Hydraulic brakes transmit force through incompressible fluid according to Pascal's law, so pressure applied at the master cylinder acts equally throughout the system.
- ABS function
- The anti-lock braking system senses wheel lock-up and rapidly modulates brake pressure, allowing the driver to steer while braking hard on slippery surfaces.
- Ohm's law
- Ohm's law states that voltage equals current multiplied by resistance (V = I × R); it is used to calculate circuit current, voltage drop or resistance.
- Alternator output voltage
- A correctly charging 12-volt alternator usually produces about 13.8 to 14.4 volts at the battery with the engine running and electrical loads switched off.
- Voltage drop test
- A voltage drop test measures the voltage lost across a circuit connection or cable while current flows; excessive drop indicates high resistance or a bad earth.
- Tyre tread wear limit
- The legal minimum tyre tread depth for cars is 1.6 millimetres across the central three-quarters of the tread around the entire circumference.
- Engine oil viscosity grade
- Oil viscosity grade such as 10W-40 indicates cold-flow and hot-flow behaviour; use the grade specified by the manufacturer for the prevailing temperature range.
- Compression test interpretation
- Low compression that rises after adding oil to the cylinder suggests worn piston rings; low compression that does not rise suggests leaking valves or head gasket.
- Diagnostic trouble code
- A diagnostic trouble code is stored by the engine control unit when a sensor or circuit exceeds its expected range; scan tools read it to guide testing.
- No-start diagnosis order
- For a no-start engine, first check battery charge and connections, then confirm fuel delivery and ignition spark before testing compression and timing.