RBSE Sec Voc Automotive key terms

The ratio of the cylinder volume when the piston is at the bottom of its stroke to the volume remaining when it is at the top. Higher values generally raise efficiency and power but demand higher-octane fuel to avoid knocking.

The small gap left between the valve stem tip and the rocker arm or cam follower. It allows for heat expansion and, if wrongly set, causes noisy operation, poor sealing, or burnt valves.

A split metal ring fitted into grooves on the piston. Compression rings seal combustion gases against the cylinder wall; oil rings scrape excess lubricant back to the sump.

The sequence of intake, compression, power and exhaust strokes that a piston completes in two crankshaft revolutions. It is the working principle of most petrol and diesel vehicle engines.

Combustion gases that escape past worn piston rings or cylinder walls into the crankcase. It raises crankcase pressure, contaminates engine oil and often shows as blue exhaust smoke.

An abrasive finishing process that restores the correct cross-hatch pattern on a rebored or worn cylinder wall. The pattern helps retain oil film and assists new piston ring bedding-in.

A calibrated tool that tightens fasteners to a specified turning moment rather than by feel. Correct use prevents stripped threads, warped cylinder heads and loosened suspension or wheel fixings.

A set of thin metal blades of marked thickness used to measure small gaps. In workshops it checks valve clearances, spark plug gaps, brake pad clearance and contact breaker points.

A safety procedure in which an energy source is switched off, isolated and locked, and a warning tag is attached. It prevents accidental starting or release of stored energy during repair work.

Wearable safety items such as goggles, gloves, boots, hearing protection and overalls. It is the last line of defence against injury and must suit the task and the hazard present.

A jack lifts a vehicle using hydraulic pressure, while rigid axle stands support it once raised. Stands must carry the load because a jack alone can creep or fail suddenly.

A condition where the clutch disc fails to transmit full engine torque, so engine speed rises without matching road speed. Common causes are a worn friction lining, oil contamination or a weak pressure plate.

The small movement of the clutch pedal before the release bearing begins to act. Too little play lets the bearing ride on the pressure plate; too much prevents full disengagement and causes difficult gear selection.

A flywheel in two parts joined by springs and a friction damper, used to absorb engine torque pulses. A failing unit causes vibration, rattle at idle and judder when pulling away.

A joint in a drive shaft that transmits power smoothly through a wide range of angles at constant speed. Split rubber boots let grit in and grease out, leading to clicking noises on turns.

A gear set that lets the driven wheels turn at different speeds while cornering. It splits drive torque and, in a final drive, also provides the last gear reduction before the wheels.

A combined gearbox and final drive assembly used in front-wheel-drive vehicles. It houses the gear sets, synchros and differential in one casing driven through the clutch.

Loss of braking force when friction material or brake fluid overheats, usually after repeated hard stops. The pedal may feel normal but stopping distance grows until components cool.

The tendency of brake fluid to absorb moisture from the air over time. Absorbed water lowers the boiling point and promotes corrosion, so fluid is replaced at the maker's interval.

An electronic system that rapidly releases and reapplies brake pressure to stop wheels locking during hard braking. It preserves steering control and is monitored by a dashboard warning lamp.

Side-to-side wobble of a brake disc as it rotates, measured with a dial gauge. Excessive runout pushes the pads back, causing pedal pulsation and uneven or premature pad wear.

Adjustment of camber, caster and toe so the wheels sit correctly relative to the road and each other. Incorrect settings cause uneven tyre wear, poor straight-line stability and heavy steering.

A sensor at each wheel that reports rotational speed to the ABS and stability control modules. A faulty or dirty sensor disables these systems and lights the warning lamp.

A test instrument that measures voltage, current and resistance, and often continuity. It is the basic tool for tracing open circuits, voltage drops and shorted or failed components.

Measuring the voltage lost across a cable, connector or earth while current flows. A high reading reveals resistance caused by corrosion or a loose joint that a simple continuity check would miss.

The vehicle's self-monitoring system that stores fault codes and live data for the engine, ABS, airbags and other modules. A scan tool reads these codes to guide diagnosis.

The rule set for working on hybrid and electric vehicle circuits, where orange cables carry dangerous voltage. Isolation, insulated gloves, lockout and maker procedures are mandatory before any work.

Safe practice for lead-acid batteries: eye protection, acid-resistant gloves, no sparks or naked flames, and neutralising spills with bicarbonate solution. Charging releases explosive hydrogen gas.

A rating of how quickly a spark plug conducts heat away from its tip. Too hot a plug can pre-ignite; too cold a plug fouls with carbon, so the maker's specification must be followed.

Abnormal, uncontrolled burning of the fuel-air charge that produces a sharp metallic rattle. It is caused by over-advanced timing, low-octane fuel, overheating or excessive carbon deposits.

A system that routes a small portion of exhaust gas back into the intake to lower combustion temperature. This reduces nitrogen oxide emissions but can cause rough running if a valve sticks open.

An exhaust device with a coated honeycomb that converts carbon monoxide, hydrocarbons and nitrogen oxides into less harmful gases. It needs correct fuel mixture and must not be contaminated by lead or oil.

A system that draws crankcase vapours back into the intake for burning instead of venting them to air. A blocked valve causes oil leaks and rough idle from unmetered air.

An exhaust-driven turbine that forces extra air into the engine, raising power for a given size. It needs clean oil and correct cooling, and worn units cause smoke and lost boost.

A temperature-operated valve that blocks coolant flow to the radiator until the engine warms up. A stuck-open unit causes slow warm-up and poor heater output; a stuck-closed one causes overheating.

The documented check of a new or repaired vehicle before handover, covering fluids, tyre pressures, lights, road test and safety items. It protects the workshop and the customer alike.

The written record of a repair, listing customer complaint, work authorised, parts used and time spent. Accurate completion supports billing, warranty claims and traceability of the repair.

A structured conversation with the vehicle owner to capture symptoms, when they occur and any recent work. Good questioning shortens diagnosis and prevents unnecessary parts replacement.

How many times stock is sold and replaced in a period, calculated as cost of goods sold divided by average stock value. It shows whether spare parts capital is being used efficiently.