UPMSP High School Automobile key terms

A wrench that measures and limits the twisting force applied to a fastener, so bolts such as cylinder-head bolts are tightened to the maker's specified value without stripping threads or distorting parts.

A set of thin metal blades of known thickness used to measure small gaps, for example valve clearance or spark plug gap, by sliding blades in until one just fits.

A measuring tool with a fixed main scale and a sliding scale that reads outside, inside and depth dimensions to a precision of about 0.02 mm, used for checking shaft and bore sizes.

A precision measuring instrument using a calibrated screw to measure thickness or diameter, typically to 0.01 mm, used for checking piston, crankshaft journal and valve stem wear.

The operating sequence of a petrol or diesel engine in which the piston makes four strokes, induction, compression, power and exhaust, with the crankshaft turning twice per complete cycle.

The ratio of the cylinder volume above the piston at bottom dead centre to the volume at top dead centre; it affects power output, thermal efficiency and the fuel octane or cetane required.

The highest position reached by the piston in the cylinder, where the crankshaft throw is vertical; ignition or injection timing and valve adjustment are referenced to this point.

The small gap left between the valve stem and the rocker arm or cam follower, allowing for thermal expansion; too little causes valves to leak, too much causes noise and lost lift.

A rotating shaft with eccentric lobes that open the inlet and exhaust valves in correct sequence and timing, driven from the crankshaft by belt, chain or gears at half crankshaft speed.

The main rotating shaft of the engine that converts the reciprocating motion of the pistons into rotary motion through crank throws, and delivers torque to the flywheel.

A cylindrical part that slides in the cylinder bore, receives combustion pressure and transmits force through the connecting rod to the crankshaft; it carries rings that seal and control oil.

A split metal ring fitted in grooves on the piston; compression rings seal combustion gases and oil-control rings scrape excess lubricant from the bore wall back to the sump.

The machined internal diameter of an engine cylinder in which the piston travels; it may be measured for taper and ovality and rebored or honed during overhaul.

Abnormal combustion in a spark-ignition engine in which the end gas ignites spontaneously ahead of the flame front, producing a sharp knocking sound, high pressures and possible piston damage.

A friction device that connects and disconnects the engine from the gearbox, allowing smooth take-up of drive from rest and interruption of power during gear changes.

A gearbox in which the driver selects fixed gear ratios by moving a lever, using synchromesh to match shaft speeds; it is simpler and usually more efficient than an automatic.

The number of teeth on the driven gear divided by the number on the driving gear; it determines the trade-off between output speed and torque multiplication in the driveline.

A gear assembly that divides drive between the two driven wheels while allowing them to rotate at different speeds when the vehicle turns a corner.

The last reduction gearing between the gearbox output and the road wheels, usually in the axle; it multiplies engine torque and sets overall road speed for each gear.

A cone-and-sleeve mechanism inside a manual gearbox that brings the selected gear and shaft to matching speed by friction before engagement, preventing gear clash.

Adjustment of camber, caster, kingpin inclination and toe so that wheels sit at the maker's specified angles, giving straight tracking and even tyre wear.

The amount by which the front edges of a pair of wheels are closer together than the rear edges, measured in millimetres or degrees, to offset the wheels' tendency to splay outward.

The backward or forward tilt of the steering axis from vertical, viewed from the side; positive caster gives self-centring and directional stability at speed.

A hydraulic damper that converts suspension spring movement into heat by forcing oil through valves, controlling bounce and keeping the tyres in contact with the road.

A suspension layout in which a combined spring and damper unit also forms the upper steering pivot, giving light weight and compact packaging in most front-wheel-drive cars.

A braking arrangement in which pedal force is transmitted through brake fluid to wheel cylinders or calipers, using Pascal's principle to multiply force at the friction surfaces.

The procedure of removing trapped air from hydraulic brake lines by opening a bleed nipple while an assistant holds the pedal down, until only bubble-free fluid emerges.

A glycol-based hydraulic brake fluid rated by its boiling point and viscosity; it absorbs moisture over time, lowering its boiling point, so it must be replaced periodically.

An anti-lock braking system that senses wheel lock-up and modulates hydraulic pressure rapidly, letting the driver brake hard while keeping steering control.

A magnetic or Hall-effect sensor mounted near a toothed rotor on the hub that reports wheel rotation rate to the ABS or engine control unit.

A lead-acid storage device that supplies current for starting, lighting and ignition and is recharged by the alternator; each cell produces about 2.1 volts.

A belt-driven generator with a rectifier that produces direct current to charge the battery and run electrical loads whenever the engine is running.

A test instrument that measures voltage, current and resistance, used to trace open circuits, check battery charge and diagnose sensors and charging faults.

A tool that draws electrolyte from a battery cell and measures its specific gravity, indicating the state of charge of that cell.

A rating of a petrol's resistance to detonation, with higher numbers allowing higher compression ratios; it is not a measure of energy content or quality in general.

A rating of a diesel fuel's ignition quality, showing how readily it self-ignites under compression; higher cetane gives easier starting and quieter combustion.

A heat exchanger at the front of the vehicle that transfers heat from engine coolant to the passing air, using fins and tubes to give a large cooling surface.

A temperature-operated valve in the coolant circuit that stays closed while the engine warms up and opens at a set temperature to send coolant through the radiator.

A mixture of water and antifreeze, usually ethylene glycol, that carries heat from the engine to the radiator and also raises the boiling point and prevents corrosion and freezing.

A measure of an oil's resistance to flow, expressed in grades such as 15W-40; the first figure shows cold performance and the second behaviour at operating temperature.

A canister or cartridge containing filter media that traps metal particles, carbon and sludge from the lubricating oil before it reaches engine bearings.

A dashboard light switched by an oil pressure sender; it glows when pressure falls below a safe level, warning of low oil, a failed pump or a blocked passage.

Combustion gases that leak past the piston rings into the crankcase, raising internal pressure and contaminating the oil; excessive blow-by indicates worn rings or bores.

A toothed belt that drives the camshaft from the crankshaft at exactly half speed; if it breaks on an interference engine, valves and pistons can collide.

A heavy disc bolted to the crankshaft that stores rotational energy to smooth the power pulses between firing strokes and provides a friction surface for the clutch.

A device screwed into the combustion chamber that carries a high-voltage spark across a small gap to ignite the compressed petrol-air mixture.

A safety procedure in which an energy source is isolated, locked and tagged before maintenance, preventing accidental starting or release of stored energy while someone works.

A rigid support placed under the chassis after a vehicle is raised, so the hydraulic jack does not carry the load while anyone works beneath the vehicle.

Wearable safety items such as goggles, gloves, safety shoes and ear protection that reduce injury risk from chemicals, sharp edges, noise and falling objects in the workshop.

Scheduled servicing such as oil and filter changes, fluid checks and belt inspection carried out at set intervals to prevent breakdowns rather than to repair faults after they occur.