Karnataka II PUC Automobile - Vocational (KSEAB) cheat sheet

Four-stroke cycle order: intake, compression, power, exhaust - one power stroke per two crankshaft revolutions.

Brake thermal efficiency = brake power ÷ heat energy supplied by fuel; indicated thermal efficiency uses indicated power instead.

Mechanical efficiency = brake power ÷ indicated power; typical spark-ignition engines reach 75–90%.

Compression ratio r = (swept volume + clearance volume) ÷ clearance volume; petrol engines typically 8:1 to 12:1.

Fire classes for extinguisher choice: A solid combustibles, B flammable liquids, C electrical, D combustible metals; CO2 suits B and C.

Workshop PPE rule: eye protection for grinding and chipping, gloves for sharp and hot parts, and never loose clothing near rotating machinery.

Jack stands must support a lifted vehicle; a hydraulic jack alone is a lifting device, not a support device.

Petrol flash point is about −43 °C, so fuel vapour ignites readily; no smoking, no open flame, and bond/earth containers when transferring fuel.

Main components: cylinder block, cylinder head, piston, piston rings, connecting rod, crankshaft, flywheel, camshaft, valves.

Piston ring functions: compression rings seal combustion gas; oil control rings scrape excess oil from the cylinder wall.

Valve clearance is measured cold with a feeler gauge between rocker arm and valve stem; too little clearance causes valve held open and burnt seats.

Firing order determines ignition or injection sequence; common four-cylinder orders are 1-3-4-2 and 1-2-4-3.

Valve timing: intake opens before TDC and closes after BDC; exhaust opens before BDC and closes after TDC, giving valve overlap.

Diesel compression ratios are roughly 16:1 to 22:1; ignition is by compression heat, not a spark plug.

Turbocharger uses exhaust gas energy to drive a turbine coupled to a compressor; a wastegate limits boost pressure.

Engine knocking (detonation) is premature uncontrolled combustion; high compression, hot spots and low octane increase it.

Petrol is rated by octane number (anti-knock quality); diesel by cetane number (ignition ease); higher cetane means shorter ignition delay.

Stoichiometric air-fuel ratio is about 14.7:1 by mass for petrol and about 14.5:1 for diesel.

Battery-coil ignition parts: battery, ignition switch, coil, contact breaker or electronic trigger, distributor, spark plugs, condenser.

Spark plug gap typically 0.6–0.9 mm; a wider gap needs higher voltage and may misfire under load.

Cooling system parts: radiator, water pump, thermostat, fan, hoses, coolant passages; the thermostat regulates coolant flow to hold operating temperature.

Coolant boils at a higher temperature under pressure; a 15 psi cap raises boiling point by roughly 25 °C.

Lubrication functions: reduce friction and wear, cool, clean, seal, and cushion shock loads; oil pressure is shown by a gauge or warning lamp.

Oil grades use SAE viscosity (for example 15W-40); the W number is the cold-flow rating, the second number the hot rating.

Clutch purpose: engage and disengage engine from transmission smoothly and transmit torque without slip when fully engaged.

Clutch parts: flywheel, friction disc, pressure plate, release bearing, release fork, clutch pedal linkage.

Clutch free play is the pedal travel before the release bearing contacts the pressure plate fingers; too little causes slip and wear.

Manual gearbox uses sliding-mesh, constant-mesh or synchromesh engagement; synchromesh cones equalise shaft speeds before dog engagement.

Gear ratio = driven gear teeth ÷ driving gear teeth; overall ratio multiplies gearbox ratio by final drive ratio.

Final drive types: crown wheel and pinion, spiral bevel, hypoid; differential allows inner and outer wheels to turn at different speeds in a turn.

Propeller shaft needs universal joints to allow angle changes and a sliding spline to absorb length changes.

Automatic transmission uses a torque converter with impeller, turbine and stator; the stator multiplies torque at low speed.

Steering ratio = steering wheel rotation ÷ road wheel rotation; higher ratio reduces effort but slows response.

Ackermann geometry makes inner front wheel turn sharper than outer wheel, reducing tyre scrub in turns.

Caster, camber, kingpin inclination and toe are wheel alignment angles; incorrect toe causes rapid tyre scrub wear.

Suspension parts: springs (leaf, coil, torsion bar), shock absorbers, control arms, bushes, anti-roll bar; shock absorbers damp spring oscillation.

Leaf spring is a progressive-rate spring; coil spring is lighter but needs location links.

Hydraulic brake principle: pedal force transmitted through fluid; force = pressure × area, so a larger wheel cylinder gives greater force.

Drum brake has shoes expanding outward; disc brake has pads clamping a rotating disc, giving better fade resistance.

Tyre marking 185/65 R15: 185 mm section width, 65% aspect ratio, radial construction, 15 inch rim diameter.

Ohm's law: V = I × R; power P = V × I = I²R = V²/R.

Lead-acid battery: each cell about 2.1 V; a 12 V battery has six cells in series; specific gravity of electrolyte indicates state of charge.

Starter motor converts electrical energy to mechanical torque through a series-wound DC motor and a Bendix or solenoid drive.

Alternator produces AC rectified by diodes to DC; it charges the battery and runs accessories while the engine runs.

Lighting circuits use fuses and relays; a fuse rating must match the circuit current, not exceed wire capacity.

Electronic control unit reads sensors (MAP, oxygen, coolant temperature, crank position) and drives actuators (injectors, ignition coils, idle valve).

OBD-II uses a standard 16-pin diagnostic connector; fault codes are read with a scan tool and cleared only after repair.

CAN bus is a twisted-pair serial network; it reduces wiring and allows modules to share sensor data.

Periodic service items: engine oil and filter, air filter, fuel filter, brake fluid, coolant, spark plugs, belt inspection.

Diagnostic sequence: verify the complaint, gather information, inspect, test, isolate the fault, repair, then confirm the repair.

Compression test: a low reading on one cylinder points to valve, ring or head gasket leakage; a wet test distinguishes rings from valves.

Cylinder leakage test uses compressed air and a percentage leak figure; listen at intake, exhaust, dipstick and radiator for the leak path.

Brake fluid is hygroscopic; moisture lowers boiling point and causes spongy pedal and corrosion, so it is replaced on schedule.

Tyre rotation evens wear; check tread depth with a gauge and inflation pressure when tyres are cold.

Battery test: check open-circuit voltage, then load test; a surface charge must be removed before testing.

Exhaust smoke diagnosis: blue smoke indicates oil burning, black smoke rich mixture, white smoke coolant or unburnt diesel.

Micrometer least count = pitch of screw thread ÷ number of divisions on thimble; typical metric micrometer reads 0.01 mm.

Vernier least count = smallest main scale division ÷ number of vernier divisions; a common vernier caliper reads 0.02 mm.

Telescope gauge and dial bore gauge measure cylinder bore; measure at top, middle and bottom and in two planes for taper and ovality.

Feeler gauge measures valve clearance and spark plug gap; Plastigauge measures bearing clearance by squeeze width.

Torque wrench applies a set torque; torque = force × perpendicular distance, and bolts are tightened in a specified sequence.

Cast iron is used for blocks and heads for damping and wear resistance; aluminium alloys save weight but need liners or treated bores.

Steel classification by carbon content: low carbon up to about 0.3%, medium 0.3–0.6%, high above 0.6%; heat treatment alters hardness and toughness.

Files cut by tooth pitch; a coarse file removes metal fast, a smooth file finishes; clean the file with a file card.

BS-VI emission norms in India set limits for CO, HC, NOx and particulate matter; BS-VI introduced particulate number limits for diesel.

Three-way catalytic converter oxidises CO and HC and reduces NOx; it needs stoichiometric air-fuel ratio to work efficiently.

EGR recirculates exhaust gas into the intake to lower combustion temperature and reduce NOx.

Diesel particulate filter traps soot and regenerates by burning it at high temperature.

Common rail diesel injection uses high-pressure rail and electronically controlled injectors for precise timing and multiple injections.

Hybrid electric vehicle combines an internal combustion engine with an electric motor and battery; regenerative braking recovers energy.

Electric vehicle uses a battery pack, motor controller and traction motor; range depends on battery capacity, mass and driving conditions.

Alternative fuels: CNG, LPG, biodiesel, ethanol blends and hydrogen; each changes energy density, storage and emission profile.