WBBSE Madhyamik Vocational Automobile key terms

A wrench that clicks or shows a reading when a set twisting force is reached, so bolts are tightened to the maker's figure without over-stretching them.

The measured turning force applied to a nut or bolt, usually in newton metres, which controls how tightly the joint is clamped and prevents loosening or thread damage.

Lifting equipment used together: the jack raises the vehicle and rigid stands hold it up, so nobody works beneath a car supported only by hydraulic pressure.

A wedge placed against a road wheel to stop the vehicle rolling while it is jacked or parked on a slope, adding a second safeguard besides the parking brake.

The reinforced section of a vehicle's underbody marked by the manufacturer where a jack may safely be placed, avoiding damage to sills, fuel lines and floor panels.

A matched group of box-ended attachments with a ratchet handle, sized to grip hex nuts and bolts firmly and reduce slipping compared with open-ended spanners.

A set of thin metal blades of known thickness, slid into a gap to measure clearance such as valve lash or spark plug gap by trial fitting.

The sequence of intake, compression, power and exhaust strokes that a piston completes in two crankshaft revolutions, used by almost all car petrol and diesel engines.

The ratio of cylinder volume with the piston at bottom dead centre to the volume at top dead centre, indicating how strongly the charge is squeezed before ignition.

The small gap left between the valve stem and rocker or cam follower so the valve still closes fully when the metal expands while the engine is hot.

Abnormal explosive burning of the fuel-air charge after spark ignition, heard as a metallic knock, caused by low octane fuel, excess advance or overheating.

A wax-operated valve that stays shut while the engine warms up and then opens to send coolant through the radiator, keeping working temperature stable.

A pressure cap that raises the boiling point of coolant by holding the system under pressure and releases excess pressure or vacuum through its valves.

A device that mixes petrol with air by drawing fuel through a jet into the airstream, supplying a combustible charge to older spark-ignition engines.

An electrically operated nozzle that sprays a measured, finely atomised quantity of fuel into the intake port or cylinder at the moment the engine control unit commands.

The proportion by mass of air to fuel reaching the engine; roughly 14.7 to 1 for petrol gives complete combustion, while richer or leaner mixtures change power and emissions.

A rating of a petrol's resistance to knocking, where higher numbers suit higher compression engines and allow more ignition advance without detonation.

A rating of how readily diesel fuel self-ignites under compression; a higher cetane number gives easier cold starting and smoother, quieter combustion.

A cartridge that traps dirt and water from diesel before it reaches the injection pump, protecting precision parts from wear and corrosion.

A measure of how thickly oil resists flow, quoted as two grades such as 15W-40, where the first number describes cold behaviour and the second hot behaviour.

A replaceable element that removes metal particles, soot and sludge from circulating engine oil so they cannot score bearings or block oilways.

A gear or rotor pump driven by the engine that pushes oil under pressure to the bearings, camshaft and other moving parts through the lubricating galleries.

A friction coupling between engine and gearbox that can be engaged or released by the driver to start from rest and to change gear smoothly.

The number of teeth on the driven gear divided by the number on the driving gear, showing whether output speed falls and turning force rises.

A gear assembly that lets the two driven wheels turn at different speeds while cornering, yet delivers drive to both through the final drive.

Adjustment of camber, caster and toe so the wheels point correctly relative to the road and each other, preventing uneven tyre wear and pulling.

The height of rubber between the grooves and the road contact surface; worn tread reduces grip in rain and fails the legal minimum.

The air pressure inside a tyre, checked cold with a gauge; too low causes overheating and sidewall flexing, too high reduces the contact patch.

A closed circuit in which brake fluid transmits pedal force through pipes to wheel cylinders, multiplying force by piston area differences.

Removing trapped air from brake lines by opening a bleed screw and pumping fluid through until no bubbles appear, restoring a firm pedal.

A glycol-based hydraulic liquid with a high boiling point that must not absorb much moisture, since water boils and causes vapour lock and a spongy pedal.

A mechanically operated brake, usually on the rear wheels, that holds a stationary vehicle and provides an emergency stopping means if the hydraulic circuit fails.

A lead-acid store of electrical energy that supplies the starter motor and, once the engine runs, is recharged by the alternator.

An engine-driven generator with a rectifier that produces direct current to recharge the battery and run electrical loads while the vehicle is in use.

A heavy-duty electric motor whose pinion engages the flywheel ring gear to crank the engine until it fires.

A thin metal strip in a holder that melts and breaks the circuit when current exceeds its rating, protecting wiring and components from overheating.

A test instrument that measures voltage, current and resistance, used to trace open circuits, shorts and charging faults in the vehicle's electrical system.

An electromagnetically operated switch that lets a small control current switch a much larger load current, such as a headlamp or horn circuit.

The distance between the centre and earth electrodes of a spark plug, set with a gauge so the spark jumps reliably without misfiring.