Assam ASSEB Higher Secondary Skill Subject Automotive key terms

Special clothing and gear worn to reduce injury risk, such as safety goggles, gloves, steel-toe boots, ear defenders and overalls. In a workshop it is the first defence against cuts, burns, eye damage and chemical splashes.

The three elements needed for combustion: fuel, oxygen and heat. Removing any one stops a fire, which is why fuel leaks are cleaned up, ventilation is controlled and the correct extinguisher is chosen for the burning material.

The dilute sulphuric acid solution inside a lead-acid battery. It is corrosive, can burn skin and eyes, and releases hydrogen gas when charging, so eye protection, ventilation and no-smoking rules apply.

A wrench that clicks, beeps or displays a reading when a set tightening force is reached. It is used for critical fasteners such as cylinder head bolts and wheel nuts so joints are neither loose nor overstressed.

A set of thin metal blades of known thickness used to measure small gaps. Common jobs include valve clearance, spark plug gap and piston ring end gap, where the blade should just slide with slight drag.

A precision measuring instrument with a calibrated screw that reads outside dimensions to hundredths of a millimetre or thousandths of an inch. It is used to check journal diameters, piston skirts and brake disc thickness.

A measuring tool with internal, external and depth jaws plus a sliding vernier scale. It gives quick readings of outside diameter, bore and depth, typically to 0.02 mm, making it a general-purpose workshop gauge.

The sequence of intake, compression, power and exhaust strokes that takes two crankshaft revolutions to complete. Each stroke is defined by piston direction and valve state, and it underlies most petrol and diesel engines.

The ratio of cylinder volume with the piston at bottom dead centre to the volume at top dead centre. Higher ratios raise thermal efficiency but increase knock risk in petrol engines, so fuel octane and chamber design matter.

The small gap between the valve stem tip and the rocker or cam follower on engines with mechanical tappets. It allows for thermal expansion; too little can hold a valve open, too much causes noise and reduced lift.

The exact crankshaft positions at which the intake and exhaust valves open and close, usually given in degrees before or after dead centre. It is set by camshaft design and alignment marks during assembly.

A sealing component clamped between the cylinder block and head. It must contain combustion pressure, coolant and oil, so it is fitted with correct torque and sequence, and its failure can mix fluids or cause overheating.

The machined inner diameter of an engine cylinder in which the piston slides. It is measured for wear, taper and ovality, and may be rebored or honed to an oversize during overhaul.

Abnormal, explosive burning of the fuel-air charge after spark ignition, heard as a metallic knock. It is caused by excessive advance, low-octane fuel, overheating or high load, and can damage pistons and bearings.

The mass of air mixed with a given mass of fuel entering the engine. Petrol engines run near 14.7:1 at stoichiometric conditions, and the ratio shifts richer or leaner with load, affecting power, economy and emissions.

An electrically controlled valve that sprays atomised fuel into the intake port or directly into the cylinder. Its opening duration, set by the engine control unit, determines the delivered quantity.

A number such as 10W-30 describing how easily oil flows at low and high temperature. The W figure relates to cold cranking behaviour and the second figure to operating-temperature thickness, guiding correct lubricant choice.

A gear, rotor or vane pump driven by the engine that pushes pressurised oil from the sump to bearings, camshaft and other moving parts. A pressure relief valve limits maximum pressure.

A heat exchanger that transfers engine coolant heat to passing air. It consists of tubes and fins, with an inlet and outlet tank, and its cap regulates system pressure and allows coolant recovery.

A temperature-sensitive valve that stays closed while the engine warms and then opens to route coolant through the radiator. A stuck-open unit causes slow warm-up; a stuck-closed one causes overheating.

A friction coupling that connects and disconnects the engine from the gearbox. The driver controls slip through the pedal, allowing smooth starts and gear changes while transmitting torque when fully engaged.

A stepped-ratio transmission in which gears on shafts are selected by shift forks and synchronisers. Different ratios match engine speed to road speed and load, and neutral disconnects drive.

A cone clutch inside a manual gearbox that brings the gear and shaft to matching speed before engagement. It prevents gear clash and allows shifting without double-declutching.

A fluid coupling used in automatic transmissions that multiplies engine torque at low speed and allows the car to idle in gear. A lock-up clutch later connects input and output for efficiency.

A gear set that splits drive to the wheels while allowing them to turn at different speeds in a corner. It also provides a final gear reduction and turns drive direction through 90 degrees in rear-wheel-drive layouts.

A joint that transmits drive through a varying angle at constant rotational speed, used on front-wheel-drive driveshafts. Its protective rubber boot retains grease and excludes dirt, and a split boot leads to rapid failure.

A system in which brake pedal force is multiplied and transmitted through incompressible fluid to wheel cylinders or calipers. Air in the fluid is compressible and causes a spongy pedal, so bleeding is essential.

The procedure of removing trapped air from brake hydraulic lines by opening a bleed screw while an assistant holds pedal pressure. It restores a firm pedal and is done in the correct sequence.

An electronic system that rapidly modulates brake pressure at each wheel to prevent lock-up during hard braking. Wheel speed sensors feed a control unit that maintains slip near an optimum for steering control.

Adjustment of suspension angles, chiefly camber, caster and toe, so wheels point correctly relative to the road and each other. Incorrect alignment causes uneven tyre wear and pulling to one side.

A suspension unit combining a coil spring, damper and the upper steering pivot in one assembly. It is compact and widely used at the front, but strut mount wear affects alignment and steering feel.

A computer that reads sensors such as airflow, throttle position, oxygen and coolant temperature, then controls fuel injection and ignition timing. It also stores diagnostic fault codes for troubleshooting.

A standardised system that lets a scan tool read fault codes and live sensor data from the engine control unit. It helps technicians locate electrical and emission faults systematically.

A test instrument that measures voltage, resistance and current. It is used to check battery voltage, circuit continuity, sensor signals and parasitic drains, making it a core electrical diagnostic tool.

The ratio of a liquid's density to that of water, measured in battery electrolyte with a hydrometer to estimate state of charge. It falls as the battery discharges and rises again on charging.

A checklist carried out before a new vehicle is handed over, covering fluid levels, tyre pressures, electrical functions, paint condition and road test. It protects both customer and dealer by catching defects early.

An alphanumeric code stored by a control unit when a monitored circuit or signal falls outside expected limits. It guides testing but does not by itself identify the failed component.

A root-cause technique that repeatedly asks why a fault occurred until the underlying process failure is found. In repair work it prevents repeat comebacks by addressing cause rather than symptom.

The manufacturer's list of maintenance operations and intervals based on time or distance. It specifies oil and filter changes, inspections and replacements, and supports warranty compliance and resale value.

A document recording a vehicle's details, customer complaint, authorised work, parts used and labour time. It links the workshop floor to billing and provides a written record if a dispute arises.

A housekeeping method using sort, set in order, shine, standardise and sustain. In a workshop it reduces lost tools, trip hazards and wasted time, and makes abnormal conditions visible at a glance.

The sales level at which total revenue equals total cost, giving neither profit nor loss. A small workshop calculates it to know how many service jobs must be billed each month to stay viable.