RBSE SS Voc Automotive key terms

Bore is the internal diameter of an engine cylinder; stroke is the distance the piston travels from top dead centre to bottom dead centre. Together they determine engine displacement and affect torque characteristics.

The ratio of total cylinder volume with the piston at bottom dead centre to the volume remaining at top dead centre. It influences power output, thermal efficiency and the fuel octane an engine requires.

The small gap set between the cam lobe or rocker arm and the valve stem tip, allowing for thermal expansion. Incorrect clearance causes noise, poor breathing and possible valve burning.

Alignment marks on the camshaft sprocket, crankshaft pulley and engine casing that must line up during assembly. Correct alignment ensures valves open in the proper relation to piston position.

The correct tightness of the belt driving the camshaft, set by a spring-loaded tensioner or gauge. Too loose causes jumping or tooth stripping; too tight overloads bearings and water pumps.

The clearance between the two ends of a piston ring when fitted squarely in the cylinder bore. It must be measured with a feeler gauge, as too little gap causes ring breakage when hot.

The fine cross-hatch scratch pattern left on a rebored cylinder wall by a honing machine. It retains oil for lubrication and helps new rings bed in during running-in.

The prescribed order and staged tightening of cylinder head or bearing cap bolts, usually spiralling outward from the centre. It prevents head distortion and gasket failure.

A calibrated hand tool that indicates or limits the twisting force applied to a fastener. It must be used within its range and recalibrated periodically for accurate engine assembly.

A precision measuring instrument with a calibrated screw spindle used to measure small thicknesses and diameters to hundredths of a millimetre. It is essential for checking journals, pistons and shims.

A gauge with a spring-loaded plunger and needle that shows small linear movements on a graduated dial. It is used to check runout, end play and gear backlash.

The small movement of the clutch pedal before the release bearing contacts the pressure plate fingers. Correct free play prevents slipping and premature release bearing wear.

A cone-and-sleeve mechanism in a manual gearbox that brings the gear and shaft speeds to match before engagement. It allows smooth shifting without crashing the gears.

A forked lever inside the gearbox that slides the synchroniser sleeve to select a gear ratio. Wear on its pads causes noisy or difficult gear engagement.

A fluid coupling with an internal stator that multiplies engine torque at low vehicle speeds in automatic transmissions. It also allows the engine to idle while the car is stationary.

An intentional axial load applied to tapered roller or ball bearings during assembly to remove clearance. It prevents shaft movement and extends bearing life when set correctly.

A cross-and-yoke coupling that transmits rotary motion between shafts meeting at an angle. It permits suspension movement and steering of driven wheels.

Camber, caster, toe and thrust angle settings that define wheel orientation relative to the vehicle and road. Correct values prevent uneven tyre wear and improve directional stability.

Even distribution of mass around a wheel and tyre assembly, achieved by adding clip-on or adhesive weights. Imbalance causes vibration, usually felt through the steering at certain speeds.

The sidewall height expressed as a percentage of the tyre's nominal section width. A lower ratio gives a wider, lower-profile tyre with stiffer handling but reduced ride comfort.

Current drawn from the battery when the ignition is off and all accessories are shut, such as by a faulty module or lamp. It causes flat batteries after standing.

Measuring the potential difference across a cable, switch or connection while current flows, to reveal excessive resistance. A good connection should show near-zero volts.

A set of diodes inside the alternator that converts the alternating current produced by the stator into direct current for battery charging. A failed diode causes low output or noisy ripple.

A two-wire serial bus protocol allowing electronic control units to share data with minimal wiring. Faults are diagnosed by measuring bus resistance and observing signal voltages.

An alphanumeric identifier stored by an electronic control unit when it detects an out-of-range signal or logic fault. It guides the technician toward the affected circuit or component.

A hand-held or PC-based device that communicates with vehicle control units to read codes, view live data and perform actuator tests. It is central to modern fault diagnosis.

A manufacturer-specified timetable of inspections, fluid changes and replacements based on time or distance. Following it reduces breakdowns and preserves warranty coverage.

The procedure that clears the maintenance reminder counter after a scheduled service. It is done through the instrument cluster controls or a scan tool, depending on the model.

An oil whose viscosity grade, such as 15W-40, spans low- and high-temperature behaviour through viscosity index improvers. The first number indicates cold-flow performance.

A hardness test that presses a hardened steel ball into a material under a known load and measures the resulting indentation. It is used to check castings and heat-treated parts.

Electrochemical attack occurring when two dissimilar metals contact each other in the presence of an electrolyte. The less noble metal corrodes, so insulation or protective coatings are used.

A refinishing undercoat supplied with a separate hardener that cures by chemical reaction. It provides strong adhesion and corrosion protection before the topcoat is applied.

A paint defect in which the cured surface has a bumpy texture resembling citrus skin. It results from incorrect gun distance, thinning, pressure or drying conditions.

The total depth of primer, colour and clear coats measured in micrometres with an electronic gauge. Too thin a film gives poor durability; too thick a film may crack.

The airbag and seat-belt pretensioner network that supplements the primary restraint of the seat belt in a collision. It must be disarmed before working near its components.

Items such as goggles, gloves, respirators and safety footwear worn to reduce injury risk. Selection depends on the hazard, and equipment must be inspected and maintained.

A document supplied with a hazardous chemical that lists its hazards, safe handling, first aid and disposal requirements. Workers must be able to access it in the workplace.

A document recording a vehicle's details, the customer's complaint, work authorised and parts used. It forms the basis for billing and for tracking workshop progress.

The volume of sales or service at which total revenue equals total costs, giving neither profit nor loss. Knowing it helps an owner set prices and plan capacity.