Assam ASSEB HSLC NSQF Automotive flashcards

34 cards. Read the term and the definition here. The deck at the top of this page is optional.

Stoichiometric air-fuel ratio

The mass ratio of air to fuel at which complete combustion occurs with no excess air or fuel; about 14.7:1 for petrol and about 14.5:1 for diesel.

Compression ratio

The ratio of cylinder volume above the piston at bottom dead centre to the volume at top dead centre; petrol engines run roughly 8:1 to 12:1, diesels 16:1 to 23:1.

Torque formula

Torque equals force multiplied by perpendicular distance from the pivot, T = F x d. A 0.5 m wrench with 60 N applied gives 30 N·m.

Micrometer least count

The smallest value a micrometer can read, usually 0.01 mm on the thimble scale; a vernier micrometer resolves 0.001 mm by adding a vernier scale.

Vernier caliper least count

The smallest measurement increment of a vernier caliper, typically 0.02 mm metric or 0.001 inch imperial; verify zero reading before measuring any part.

Feeler gauge use

A set of thin steel blades of known thickness used to measure gaps such as valve clearance, spark plug gap and bearing end float by trying successive blades.

Four-stroke cycle

Intake, compression, power and exhaust strokes complete one cycle in two crankshaft revolutions; the camshaft turns once, opening each valve once per cycle.

Firing order

The sequence in which cylinders are ignited, such as 1-3-4-2 on many four-cylinder engines; it balances load on the crankshaft and must be identified before timing work.

Valve clearance

The small gap between the rocker or cam follower and valve stem, set cold with a feeler gauge; too tight burns valves, too loose causes noise and reduced lift.

Clutch free play

The pedal travel before the release bearing contacts the pressure plate, typically 10-25 mm; incorrect free play causes slip or incomplete disengagement and gear crunch.

Gear ratio calculation

Driven gear tooth count divided by driving gear tooth count; overall ratio is gearbox ratio multiplied by final drive ratio, affecting torque and speed.

Synchromesh function

Cone-shaped friction rings equalise the speed of the gear and the output shaft before the dog teeth engage, allowing smooth gear selection without crashing.

Torque converter

A fluid coupling with an impeller, turbine and stator used in automatic transmissions; it multiplies torque at low speed and allows the engine to idle in gear.

CV joint types

Outer Rzeppa joints allow steering articulation; inner tripod or double-offset joints allow plunge as suspension moves. A split boot causes grease loss and failure.

Brake hydraulic pressure

Pressure equals force divided by piston area, P = F/A; a larger master cylinder piston produces lower line pressure from the same pedal force.

DOT 3 versus DOT 5

DOT 3 and DOT 4 are glycol-based and absorb moisture; DOT 5 is silicone-based and must never be mixed with glycol fluid in the same system.

Caster angle effect

The forward or backward tilt of the steering axis; positive caster improves straight-line stability and self-centring but increases steering effort.

MacPherson strut

A suspension design combining a coil spring, damper and upper pivot in one unit, with a lower wishbone; it is compact and common on front-wheel-drive cars.

Ohm's law

Voltage equals current multiplied by resistance, V = I x R. A 12 V circuit drawing 5 A has 2.4 ohm resistance and dissipates 60 W.

Series versus parallel circuits

In series the current is common and voltages add; in parallel the voltage is common and currents add. Most vehicle loads are wired in parallel.

Battery specific gravity

The density of electrolyte compared with water; a fully charged lead-acid cell reads about 1.265, falling toward 1.120 when discharged.

Alternator charging voltage

Regulated output of about 13.8 to 14.5 V with the engine running; a reading below 13 V indicates a charging system fault such as a worn belt or failed regulator.

CAN bus resistance

Two 120 ohm terminating resistors in parallel give about 60 ohm between CAN-H and CAN-L with the bus unpowered and modules asleep.

Oil viscosity grade meaning

In SAE 10W-40, the number before W indicates cold-flow behaviour and the number after indicates viscosity at operating temperature; both are defined by test standards.

Coolant mixture ratio

A 50:50 mix of glycol antifreeze and water gives freeze protection near -37 °C and raises the boiling point when pressurised by the radiator cap.

Thermostat function

A temperature-operated valve that stays closed while the engine warms and opens to route coolant through the radiator, maintaining stable operating temperature.

Crumple zone purpose

A designed deformable front or rear structure that absorbs collision energy through controlled deformation, protecting the rigid passenger safety cell from intrusion.

Monocoque body construction

A design in which the body panels and floor form the load-bearing structure without a separate chassis, giving lower weight and greater torsional stiffness.

Bolt property class marking

Numbers such as 8.8 or 10.9 on a metric bolt head indicate tensile strength and yield ratio; grade 8.8 is common, 10.9 is high strength.

Torque-to-yield bolt

A bolt tightened past its elastic limit and permanently stretched; it must be replaced after removal and is often tightened by a specified angle rather than torque alone.

Compression test interpretation

Low dry compression that rises after adding oil indicates worn piston rings; a reading that stays low suggests leaking valves or a head gasket fault.

Break-even point formula

Fixed costs divided by the difference between unit selling price and variable cost per unit; it gives the number of jobs or units needed to cover all costs.

Used oil disposal rule

Drain used engine oil into a labelled, closed container and hand it to an authorised recycler; never pour it into drains, soil or general waste.

Refrigerant recovery requirement

Refrigerant must be recovered with approved equipment before opening an air-conditioning circuit; releasing it to the atmosphere is prohibited by environmental regulations.