Odisha CHSE +2 Vocational Automobile Technology cheat sheet

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

Compression ratio = (swept volume + clearance volume) / clearance volume; petrol engines typically 8:1 to 12:1, diesel 16:1 to 22:1.

Engine capacity (cc) = (π/4) × bore² × stroke × number of cylinders, with bore and stroke in cm.

Brake power (kW) = 2πNT/60 000 with torque T in N·m and speed N in rpm; indicated power = brake power + friction power.

Mechanical efficiency = brake power / indicated power; volumetric efficiency = actual air intake / theoretical swept volume.

Firing order spreads power strokes: common inline-4 orders are 1-3-4-2 and 1-2-4-3; inline-6 commonly 1-5-3-6-2-4.

Workshop 5S: sort, set in order, shine, standardise, sustain; keep aisles and fire exits clear at all times.

Torque wrench use: set to specified N·m, tighten in stages and in a diagonal/star sequence for cylinder heads and wheel nuts.

Valve clearance is measured with a feeler gauge when the engine is cold (or per maker's hot setting); too little clearance causes valve leakage and burnt valves.

Cylinder bore wear is checked with a bore gauge or inside micrometer at top, middle and bottom in two planes at 90°; taper and ovality limits decide reboring.

Piston ring end gap is measured by squaring the ring in the bore with a piston; too small a gap causes ring breakage when hot.

Cylinder head warpage is checked with a straight edge and feeler gauge; typical permissible limit about 0.05–0.10 mm, beyond which the head is resurfaced or replaced.

Valve seat angle is commonly 45° with 30° or 45° valves; valve face is ground to match and lapped with paste for a continuous contact band.

Crankshaft journal ovality and taper are measured with a micrometer in two planes; grinding requires undersize bearings matched to the reground size.

Engine overhaul sequence: remove, clean, inspect and measure, replace worn parts, assemble to torque and clearance specs, run in and re-check.

Blue/grey exhaust smoke indicates oil burning (worn rings, valve guides, turbo seals); black smoke indicates rich mixture or restricted air intake.

Clutch function: engage and disengage engine from transmission smoothly; free play at pedal is typically 10–25 mm and must allow full release.

Single-plate dry clutch parts: flywheel, friction disc, pressure plate, release bearing, release fork, diaphragm spring or coil springs.

Clutch slip symptoms: engine speed rises without vehicle speed; causes include worn facing, weak spring, oil contamination, no free play.

Gear ratio = driven gear teeth / driving gear teeth; overall ratio = gearbox ratio × final drive ratio; lower ratio number means higher speed.

Constant-mesh gearbox uses helical gears in permanent mesh with dog clutches; synchromesh adds a cone and baulk ring to equalise speeds before engagement.

Differential allows inner and outer wheels to turn at different speeds on turns; crown wheel and pinion ratio is the final drive ratio.

Differential gear formula: N1 + N2 = 2 × N3 for sun gears and planet gears in a standard bevel differential.

Automatic transmission fluid level is checked with the engine running and selector in P or N at operating temperature per manufacturer's procedure.

Hydraulic brake principle: Pascal's law - pressure applied to a confined fluid is transmitted equally in all directions; force = pressure × area.

Brake pedal ratio and wheel cylinder area determine braking force; a larger wheel cylinder gives more force but longer pedal travel.

DOT 3 and DOT 4 brake fluids are glycol-based and hygroscopic; DOT 5 is silicone-based and must not be mixed with glycol fluids.

Brake fade is loss of friction from heat; bleeding removes air from hydraulic lines, starting at the wheel farthest from the master cylinder.

Steering ratio = steering wheel rotation / road wheel rotation; rack-and-pinion converts rotation to linear movement of the tie rods.

Ackermann principle: on a turn the inner wheel steers at a larger angle than the outer wheel to avoid tyre scrub.

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

Suspension types: MacPherson strut, double wishbone, leaf spring, coil spring with shock absorber; shock absorbers damp oscillation, springs carry load.

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

Lead-acid battery: 12 V nominal from six 2.1 V cells; specific gravity of electrolyte about 1.260 when fully charged, 1.120 when discharged.

Battery capacity in Ah = current (A) × time (h); cold cranking amps (CCA) rate starting ability at low temperature.

Alternator output is three-phase AC rectified by diodes to DC; the voltage regulator holds about 13.8–14.5 V with the engine running.

Starter motor is a series-wound DC motor with a Bendix or pre-engaged pinion and solenoid; high current draw with slow cranking suggests a worn brush or earth fault.

Ignition coil steps battery voltage up to 15–30 kV; electronic ignition uses a sensor (Hall effect, inductive or crank position) to trigger the coil.

Headlamp circuit: battery → fuse → switch → relay → lamp → earth; a relay protects the switch from full lamp current.

LED and halogen lamps are polarity sensitive; CAN bus wiring uses twisted pairs and needs correct termination resistance, typically 120 Ω.

Stoichiometric air-fuel ratio is about 14.7:1 by mass for petrol; rich mixture (lower ratio) gives more power, lean mixture gives better economy.

Carburettor circuits: float, idle, main, power, accelerator pump and choke; venturi depression draws fuel into the air stream.

Fuel injection delivers fuel under pressure (port injection typically 2–4 bar, common rail diesel up to 2000 bar) controlled by the ECU.

Diesel fuel injection timing is set in degrees before top dead centre; late timing gives white smoke and poor power.

SAE viscosity grade like 10W-40: lower W number means better cold flow, higher second number means thicker at operating temperature.

Lubrication system: sump → strainer → oil pump → filter → galleries → bearings → return to sump; oil pressure warning lamp indicates low pressure.

Cooling system: water pump circulates coolant through block, head and radiator; thermostat opens about 80–90 °C; pressure cap raises boiling point.

Coolant is a mix of water and antifreeze (ethylene glycol), commonly 50:50; never open a hot pressurised radiator cap.

Periodic service intervals: engine oil and filter, air filter, fuel filter, brake fluid, coolant and spark plugs each have maker-specified intervals.

Daily or pre-trip checks: engine oil, coolant, brake fluid, tyre pressure and tread, lights, horn, wipers, mirrors.

OBD-II diagnostic trouble codes (P, B, C, U prefixes) are read with a scan tool; the code identifies the circuit, not always the failed part.

Tyre rotation patterns depend on drive type; radial tyres must not be cross-fitted from one side to the other in some patterns.

Tread depth minimum is 1.6 mm in many jurisdictions; check with a tread depth gauge at three points across the tread.

Engine tune-up includes valve clearance, ignition timing, spark plug gap, idle speed and air-fuel mixture adjustment (where applicable).

Compression test: crank with throttle open and all plugs removed; low reading on one cylinder suggests valve or ring fault; wet test isolates rings.

Brake inspection: pad thickness, disc run-out, drum ovality, hose condition, fluid level and moisture content.

Ferrous materials: cast iron for blocks, alloy steel for crankshafts and gears, mild steel for chassis; non-ferrous: aluminium alloy for pistons and heads, copper for wiring.

Cast iron is brittle but wear resistant and damps vibration; aluminium is light with good heat conduction and needs liners or coated bores.

Common tools: ring spanner, open-end spanner, socket set, torque wrench, screwdriver, pliers, chisel, hacksaw, puller, bearing press.

Micrometer reads to 0.01 mm; vernier calliper to 0.02 mm; dial bore gauge and telescopic gauge for internal diameters.

Feeler gauge measures valve clearance and gap; plastigauge measures bearing oil clearance; dial indicator measures run-out and end play.

Vernier least count = smallest main scale division / number of vernier divisions; for a 0.5 mm main scale and 50 divisions, least count is 0.01 mm.

Taps cut internal threads, dies cut external threads; a thread pitch gauge identifies thread size and pitch.

Safety: use correct size tools, wear goggles and gloves, never use a grinder without a guard, disconnect battery before electrical work.

Motor Vehicles Act, 1988 (India) with amendments: driving licence, registration, insurance, fitness certificate and permit requirements.

Driving licence categories include learner's licence, permanent licence and transport vehicle endorsement; learner licence validity is six months.

Mandatory documents while driving: valid licence, registration certificate, insurance certificate, pollution under control (PUC) certificate, and permit for transport vehicles.

Helmets are mandatory for two-wheeler riders and pillion riders; seat belts are mandatory for front-seat occupants.

Blood alcohol limit for private drivers in India is 30 mg per 100 mL of blood; stricter penalties apply for repeat and dangerous offences.

Bharat Stage (BS) emission norms regulate CO, HC, NOx and particulate matter; BS-VI requires ultra-low-sulphur fuel and OBD and DPF/SCR systems.

PUC certificate must be renewed at prescribed intervals (commonly six months for new vehicles, then annually) at authorised emission testing centres.

Road signs: mandatory (red circle), cautionary (triangle), informatory (blue rectangle); traffic lights follow red-stop, amber-caution, green-go.