WBCHSE HS Vocational Automobile flashcards
WBCHSE HS Vocational Automobile · Build recall with a focused review session.
32 cards. Read the term and the definition here. The deck at the top of this page is optional.
- Compression ratio formula
- Compression ratio equals swept volume plus clearance volume, divided by clearance volume. Petrol engines typically run 8:1 to 12:1; diesel engines typically 16:1 to 22:1.
- Engine displacement
- Total swept volume of all cylinders, calculated as bore area times stroke times number of cylinders, with bore area equal to pi times diameter squared divided by four.
- Fire extinguisher selection
- Water suits class A solids only. CO2 and dry powder suit flammable liquids and live electrical equipment. Never apply water to fuel or electrical fires in a workshop.
- Jack stand rule
- A hydraulic jack lifts but does not support. Place jack stands under the manufacturer's lifting points before any part of the body goes beneath the vehicle.
- Valve clearance measurement
- Measured with a feeler gauge between rocker and valve stem, usually with the engine cold. The largest blade entering with slight drag gives the clearance.
- Cylinder taper and ovality
- Taper is the bore diameter difference between top and bottom of ring travel. Ovality is measured at ninety degrees to the thrust axis using a bore gauge.
- Torque-to-yield head bolts
- Tightened in stages to a low torque then rotated a specified angle. They stretch permanently and must be replaced rather than reused at overhaul.
- Head gasket failure signs
- Coolant contaminated with oil, bubbles in the radiator, white exhaust smoke and compression loss between adjacent cylinders all indicate a breached head gasket.
- Piston ring end gap
- Checked by squaring the ring in its bore with a piston. Too small a gap causes ring butting and breakage as the ring expands with heat.
- Gear ratio calculation
- Driven gear teeth divided by driving gear teeth. Overall ratio is gearbox ratio multiplied by final drive ratio, giving total torque multiplication.
- Clutch slip test
- Select a high gear at low road speed and accelerate hard. Engine speed rising without matching road speed indicates a slipping clutch friction plate.
- Camber caster and toe
- Camber is wheel vertical tilt, caster is steering axis tilt, and toe is the front-to-rear track difference between the wheels, set to manufacturer specification.
- CV joint click diagnosis
- Clicking from a front wheel during full-lock acceleration indicates a worn outer constant velocity joint, usually caused by a split boot losing grease.
- Brake bleeding sequence
- Air in the hydraulic circuit makes the pedal spongy. Bleed starting at the wheel farthest from the master cylinder, keeping the reservoir topped up throughout.
- Brake fade cause
- Overheated pads or boiled hygroscopic brake fluid reduces retardation and lengthens the pedal. DOT 3 and DOT 4 fluids absorb moisture over time.
- Braking distance versus speed
- Braking distance increases with the square of speed, so doubling speed quadruples the distance. Total stopping distance adds thinking distance to braking distance.
- ABS warning lamp meaning
- A lamp that stays on after the self-test means anti-lock control is disabled. Base hydraulic braking still works but wheels can lock under hard braking.
- Ohm's law and power
- Voltage equals current times resistance. Power equals voltage times current, or current squared times resistance, or voltage squared divided by resistance.
- Series and parallel circuits
- In series the current is common and voltages add. In parallel the voltage is common and currents add, so parallel loads draw more total current.
- Charging voltage check
- With the engine running and electrical loads off, battery terminal voltage should read about 13.8 to 14.5 volts for a healthy alternator and regulator.
- CAN bus fault symptom
- A shorted twisted pair or missing termination resistor stops module communication, producing multiple unrelated fault codes and non-starting or inoperative accessories.
- OBD-II code letters
- P denotes powertrain, B body, C chassis and U network codes. The second character shows whether the code is generic or manufacturer specific.
- Wet and dry compression test
- Cranking with throttle open and plugs removed gives dry readings. Repeating with oil added raises compression only if rings are worn, not valves.
- Cylinder leakage test
- Compressed air is fed into a cylinder at TDC. Air heard at the intake, exhaust or oil filler identifies inlet valve, exhaust valve or ring leakage.
- Tyre tread legal minimum
- The minimum tread depth in major grooves is 1.6 millimetres. Pressures are checked cold and set to the tyre placard value for the load.
- Vernier calliper least count
- Smallest main scale division divided by the number of vernier divisions. A typical metric calliper with 0.5 mm divisions and 25 vernier parts reads to 0.02 mm.
- Micrometer reading method
- Read the main scale in millimetres, then add the thimble value, where each thimble division represents 0.01 mm on a standard 0 to 25 mm micrometer.
- Feeler gauge use
- A set of blades of known thickness measures gaps such as valve clearance and spark plug gap. The correct value is the largest blade entering with slight drag.
- Plastigauge bearing clearance
- A plastic thread is placed across the journal, the cap is torqued, then the crushed width is compared to a scale to give the oil clearance.
- Break-even point formula
- Fixed costs divided by the difference between selling price per unit and variable cost per unit gives the number of units needed to cover all costs.
- Gross versus net profit
- Gross profit is sales minus cost of goods sold. Net profit subtracts operating expenses such as rent, wages and utilities from gross profit.
- Job card purpose
- Records customer details, reported complaint, work performed, parts used and technician sign-off, giving traceability for warranty claims and repeat repairs.