BTEB Automotive Mechanics key terms

Special clothing and gear worn to reduce injury risk, such as safety goggles, gloves, hearing protectors, steel-toe boots, and coveralls. It supplements, but never replaces, safe work practices and machine guards.

A procedure for isolating energy sources and attaching locks and warning tags before servicing equipment, so a machine cannot start or release stored energy while someone is working on it.

Physical barriers or devices fitted around belts, pulleys, shafts, and cutting points to prevent body parts or clothing from contacting moving parts. Guards must remain fitted whenever the machine runs.

A measuring tool with a fixed main scale and a sliding vernier scale, used to read outside, inside, and depth dimensions. The vernier division allows readings finer than the smallest main-scale division, commonly 0.02 mm.

A precision instrument using a calibrated screw and thimble to measure small thicknesses or diameters. The spindle moves one pitch per revolution, so thimble divisions give readings typically to 0.01 mm.

The smallest change in a quantity that an instrument can display or distinguish. For a vernier caliper it equals one main-scale division divided by the number of vernier divisions.

A set of thin metal blades of known thickness used to check small gaps, such as valve clearances, spark plug gaps, or piston ring end gaps. The blade that fits with slight drag indicates the clearance.

A wrench that indicates or limits applied turning force so fasteners are tightened to a specified torque. Correct use prevents stretched bolts, distorted parts, and loosened joints on critical assemblies.

The operating sequence of a reciprocating engine in which each cylinder completes intake, compression, power, and exhaust strokes in two crankshaft revolutions. One power stroke occurs per cylinder per cycle.

The ratio of cylinder volume above the piston at bottom dead centre to the volume at top dead centre. It strongly influences power output, thermal efficiency, and fuel octane requirement.

The small gap between the valve stem and the rocker or cam follower when the valve is closed. It allows for thermal expansion and is checked and adjusted to the manufacturer's specification.

The precise crankshaft positions at which the intake and exhaust valves open and close, usually expressed in degrees before or after top or bottom dead centre. It is set by camshaft design and timing marks.

A prescribed order, usually spiralling from the centre outward, for tightening head bolts in stages to a specified torque. It distributes clamping load evenly and prevents gasket leaks and head distortion.

Abnormal combustion in which the end gas ignites spontaneously and burns explosively after the spark, producing a sharp knocking sound. Causes include excessive compression, advanced timing, overheating, and low-octane fuel.

A friction device that connects and disconnects engine power to the transmission, allowing smooth starts and gear changes. The pressure plate clamps the driven disc against the flywheel when the pedal is released.

The small clearance at the start of a pedal or lever travel before a component begins to act, such as clutch pedal free play. Correct free play prevents slipping and premature release bearing wear.

A stepped-ratio transmission in which gears on shafts are selected by a shift fork mechanism to give several forward speeds and one reverse. Ratio changes match engine speed to road speed and load.

The number of teeth on the driven gear divided by the number of teeth on the driving gear. It shows how many turns the input makes for one turn of the output, and hence the speed and torque change.

A gear assembly that divides drive torque between two half shafts while allowing them to rotate at different speeds during turns. It also provides a final speed reduction through its crown wheel and pinion.

A flexible coupling, usually a cross-and-yoke type, that transmits torque through a changing angle between shafts. It is commonly used at each end of a propeller shaft in rear-wheel-drive vehicles.

The quantity of charge a battery can deliver, expressed in ampere-hours, usually rated at a specified discharge rate. It indicates how long the battery can supply a given current before reaching a low voltage.

The ratio of a liquid's density to that of water, used in a hydrometer to estimate battery state of charge. A reading near 1.260 indicates a charged lead-acid cell; near 1.120 indicates discharged.

A belt-driven generator that produces alternating current, which is rectified by diodes to charge the battery and run vehicle loads. Its output is regulated to a set voltage, typically about 14 volts.

The crankshaft position, usually in degrees before top dead centre, at which the spark plug fires. Correct timing balances power, economy, and emissions while avoiding detonation.

A system in which brake pedal force is transmitted through incompressible fluid to wheel cylinders or calipers, which press friction linings against rotating surfaces. It multiplies force and gives balanced braking.

A temporary loss of braking force caused by overheating of linings or fluid, reducing friction or boiling fluid to form compressible vapour. It is reduced by cooling, suitable lining material, and correct adjustment.

The process of removing trapped air from a hydraulic brake circuit by opening bleeder screws and expelling fluid until bubble-free fluid flows. Air is compressible and causes a spongy pedal.

The forward or backward tilt of the steering axis from vertical, viewed from the side. Positive caster improves straight-line stability and self-centring of the steering after a turn.

The inward or outward tilt of a wheel from vertical, viewed from the front. Excessive camber causes uneven tyre wear and can affect directional stability and cornering grip.

The amount by which the front edges of a pair of wheels are closer together (toe-in) or farther apart (toe-out) than the rear edges. It compensates for suspension movement and controls tyre scrub.

The chemically ideal mass ratio of air to fuel for complete combustion, about 14.7 to 1 for petrol. Ratios richer or leaner than this leave unburned fuel or excess oxygen in the exhaust.

The mass of air supplied to an engine compared with the mass of fuel. It determines combustion quality, power, fuel consumption, and exhaust emissions across different operating conditions.

A measure of an oil's resistance to flow, graded by SAE numbers such as 10W-30. Multigrade oils flow easily when cold yet maintain film strength when hot, protecting bearings and moving parts.

A device, usually gear or rotor type, that draws oil from the sump and delivers it under pressure to bearings, camshaft, and other moving parts. A relief valve limits maximum pressure.

A temperature-sensitive valve in the cooling circuit that stays closed while the engine warms and opens at a set temperature to allow coolant flow to the radiator. It keeps the engine at its design temperature.

A mixture of water and antifreeze, usually ethylene glycol, circulated to carry heat from the engine to the radiator. It also raises boiling point, lowers freezing point, and inhibits corrosion.

A planned list of inspections, adjustments, and replacements performed at specified time or distance intervals. Following it reduces breakdowns, extends component life, and keeps the vehicle safe and efficient.

A systematic process of gathering symptoms, forming likely causes, and testing them in logical order to locate a fault. It avoids random parts replacement and restores the system efficiently.

Any condition, substance, or activity in the workshop with potential to cause harm, such as slipping, fire, fumes, or electrical contact. Hazards are identified, assessed, and controlled before work begins.

A structured evaluation of what could cause harm, how likely and severe it is, and what controls are needed. It is recorded, reviewed, and communicated to everyone affected by the work.

A document supplied with a hazardous substance that lists its hazards, safe handling, storage, first-aid, and spill measures. Workers must consult it before using unfamiliar chemicals.

Separating waste such as used oil, solvents, batteries, and metal scrap into distinct streams for safe disposal, recycling, or treatment. It prevents pollution and complies with environmental regulations.

The use of trays, bunds, absorbents, and prompt clean-up to stop leaked fuel, oil, or chemicals spreading into drains or soil. Quick containment protects people, water, and the environment.