Assam ASSEB Higher Secondary Skill Subject Automotive flashcards

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

Fire triangle

The three elements needed for combustion: fuel, oxygen and heat. Removing any one extinguishes the fire, which is why fuel and electrical fires need CO2 or dry powder rather than water.

Jack stand rating

The maximum load a stand can safely support. It must exceed the vehicle kerb weight, and stands are placed under chassis jacking points because a hydraulic jack is a lifting device, not a support.

Micrometer least count

The smallest reading a micrometer can show, calculated as screw pitch divided by thimble divisions. A 0.5 mm pitch with 50 thimble divisions reads to 0.01 mm.

Vernier caliper least count

The smallest measurement the caliper resolves, found by dividing one main scale division by the number of vernier divisions. A 1 mm main division with 20 vernier divisions gives 0.05 mm.

Torque wrench calibration

Verification that indicated torque matches applied torque. Wrenches are checked at mid-scale on a calibrated rig and rechecked periodically, because overload and poor storage cause reading drift.

Compression ratio

Swept volume plus clearance volume divided by clearance volume. Petrol engines typically run 8:1 to 12:1, while diesel engines run higher, commonly 16:1 to 23:1.

Firing order

The sequence in which cylinders receive ignition or injection. It determines crankshaft layout and ignition sequencing; common in-line four orders are 1-3-4-2 and 1-2-4-3.

Torque-to-yield bolts

Cylinder head or suspension bolts tightened past their elastic limit so they stretch permanently. They must be replaced each time and tightened in the specified sequence, usually from the centre outwards.

Stoichiometric air-fuel ratio

The air-to-fuel mass ratio giving complete combustion. For petrol it is about 14.7:1; richer mixtures carry excess fuel and leaner mixtures carry excess air.

Octane and cetane numbers

Octane rates petrol resistance to knocking, while cetane rates diesel ignition quality. Higher octane resists pre-ignition; higher cetane shortens ignition delay and eases cold starting.

SAE viscosity grade

A two-part oil rating where the number before W describes cold flow and the number after describes hot viscosity. A 5W-30 flows better when cold than a 15W-40.

Clutch pedal free play

The small travel before the release bearing contacts the pressure plate, typically 10 to 25 mm. Too little free play lets the bearing drag and slip the clutch; too much prevents full disengagement.

Synchroniser baulk ring

A brass or steel cone ring that frictionally equalises shaft speeds before gear engagement. Worn rings let the gear clash or crunch, especially on fast downshifts.

Final drive ratio

Ring gear teeth divided by pinion teeth. A numerically higher ratio multiplies torque for pulling power; a lower ratio allows higher road speed at a given engine speed.

Torque converter stall test

A test holding the brakes and opening the throttle briefly to reach maximum engine speed against the converter. The stall speed indicates converter, engine power and one-way clutch condition.

Hydraulic pressure formula

Pressure equals force divided by piston area, so a larger caliper piston produces more clamping force for a given pedal force but also increases pedal travel and fluid displacement.

Brake fluid hygroscopy

The tendency of DOT 4 fluid to absorb moisture from air. Water lowers the boiling point and promotes corrosion, so fluid is replaced about every two years or when moisture exceeds roughly 3 percent.

Tyre wear diagnosis

Reading wear patterns to find faults: centre wear means over-inflation, both shoulders mean under-inflation, one shoulder means camber or toe error, and cupping means worn dampers.

Wheel alignment angles

Toe is the difference in distance between front and rear of the tyres, camber is vertical tilt, and caster is steering axis tilt. Incorrect toe rapidly wears tyre shoulders.

Ohm's law

Voltage equals current multiplied by resistance, and power equals voltage multiplied by current. A 12 volt circuit drawing 5 amps has 2.4 ohms resistance and dissipates 60 watts.

Battery resting voltage

The open-circuit voltage of a settled battery. About 12.6 volts means fully charged, below 12.4 volts means partly discharged, and cranking below about 9.6 volts suggests a weak battery.

Voltage drop test

Measuring voltage lost across a cable or connection while the circuit carries current. More than about 0.5 volts indicates excessive resistance and is more reliable than a resistance test on high-current circuits.

CAN bus

A twisted-pair differential network linking control modules. Both lines sit near 2.5 volts at rest, and a shorted or open line can disable many modules at once.

Paint film thickness

The total dry thickness of primer, base coat and clear coat, commonly 80 to 150 micrometres on a car. Measuring it reveals previous repairs and helps match new paint.

Orange peel defect

A stippled paint surface resembling orange skin, caused by too little thinner, excessive air pressure or incorrect spray distance. It is corrected by sanding and polishing or recoating.

Panel gap and flush

The even spacing and level alignment between body panels, commonly 4 to 6 mm at doors. Uneven gaps indicate hinge wear, frame damage or poor panel adjustment after repair.

Tread depth limit

The legal minimum tread depth of 1.6 mm across the central three-quarters of the tyre. Replacing before this limit preserves wet grip and resists aquaplaning.

Cold tyre pressure rule

Tyre pressure is set cold because heat raises it about 0.1 bar per 10 degrees Celsius. Hot readings must never be corrected downward, or the tyre will end up under-inflated.

Diagnostic trouble code

A stored code identifying the circuit or system where the control unit detected a fault. It does not always name the failed part, so circuit testing is still required.

Fuel trim interpretation

Short-term plus long-term trim beyond about 10 percent signals a mixture fault. Positive trim means the control unit is adding fuel to correct a lean condition.

Cylinder leakage test

Compressed air is fed into a cylinder at top dead centre to locate leaks. Air heard at the intake means an intake valve leak, at the exhaust an exhaust valve leak, and in the crankcase worn rings.

Break-even volume

The number of jobs needed to cover costs, calculated as fixed costs divided by price minus variable cost per job. Above this volume the workshop makes a profit.