UPMSP High School Automobile cheat sheet

Automobile classification by fuel: petrol (SI engine, spark plug ignition), diesel (CI engine, compression ignition), CNG/LPG (spark ignition with gas mixer or sequential injection), electric (battery + motor, no combustion).

Main vehicle systems: engine (power), transmission (torque/speed conversion), steering, suspension, braking, electrical, fuel, lubrication, cooling. Chassis = frame + running gear; body = load/passenger enclosure.

Fire classes and extinguishers: Class A solid, Class B flammable liquid, Class C electrical, Class D metal. Petrol fires need foam, dry powder or CO2 - never water; electrical fires need CO2 or dry powder.

Workshop PPE rules: safety goggles for grinding/chiselling, gloves for handling hot parts and sharp sheet metal, safety shoes for heavy components, ear protection above ~85 dB, respirator for paint/solvent and brake dust.

Jack and stand rule: a hydraulic jack lifts only; axle stands or ramps must support the vehicle before any part of the body goes under it. Chock the wheels diagonally opposite the lifted corner.

Battery and fuel safety: disconnect the earth (negative) terminal first and reconnect it last; no sparks or smoking near charging batteries (hydrogen gas); keep fuel away from hot exhaust and electrical arcs.

Compressed air and cleaning: never direct an air jet at skin (air embolism risk); use a vacuum or wet method for brake and clutch dust; solvents must be used with ventilation, and used oil is a hazardous waste.

First aid essentials: burns - cool with running water for at least 10–20 minutes, do not burst blisters; eye foreign body - do not rub, flush and refer; electric shock - isolate supply before touching the casualty.

Four-stroke SI cycle: induction, compression, power (spark ignition), exhaust - two crankshaft revolutions per cycle. Four-stroke CI cycle: same strokes but fuel is injected near the end of compression and ignites from heat of compression.

Compression ratio CR = (swept volume + clearance volume) / clearance volume = (Vs + Vc) / Vc. Swept volume Vs = (π/4) d² L × n for n cylinders.

Engine capacity = (π/4) d² L × number of cylinders; bore d and stroke L in the same units as the result.

Valve timing: valve overlap occurs around TDC between exhaust closing and inlet opening; too much overlap at low speed causes rough idle and exhaust backflow. Valve clearance is set cold on most engines and is needed for thermal expansion.

Firing order determines crankshaft and distributor sequencing; common in-line four orders are 1-3-4-2 and 1-2-4-3. Firing interval = 720° / number of cylinders for a four-stroke.

Main parts: cylinder block, head, piston with rings (compression + oil control), connecting rod, crankshaft, camshaft, flywheel, valves and springs. Piston rings seal combustion gas, control oil and transfer heat to the wall.

Diesel specifics: fuel injector, high-pressure pump, glow plugs (cold start aid), and much higher compression ratio than petrol; injector nozzle spray pattern affects combustion quality.

Turbocharger uses exhaust gas energy to drive a compressor; a wastegate limits boost. Symptoms of a failed head gasket: white smoke, coolant loss, oil contamination, bubbles in the radiator.

Clutch purpose: connect and disconnect engine from transmission smoothly. Single-plate dry clutch parts: flywheel, friction disc, pressure plate, release bearing, release fork, cable or hydraulic actuation.

Clutch faults: slip (engine revs rise without speed - worn disc, weak spring, oil on friction face), drag (difficulty engaging gears - air in hydraulics, warped disc), judder (loose mounts, oil, warped flywheel).

Manual gearbox: sliding-mesh, constant-mesh and synchromesh types. Synchromesh cones equalise shaft speeds before dog engagement, so no double-declutching is needed.

Gear ratio = driven teeth / driving teeth = input speed / output speed. Overall ratio = gearbox ratio × final drive ratio. Lower ratio number = higher speed, less torque.

Final drive and differential: crown wheel and pinion reduce speed and turn drive through 90°; the differential allows inner and outer wheels to rotate at different speeds in a turn while still transmitting torque.

Automatic transmission: torque converter (impeller, turbine, stator) replaces the clutch and multiplies torque at low speed; planetary gearsets and a valve body provide ratios; ATF also acts as hydraulic fluid and cooler.

CVT uses two variable-diameter pulleys and a steel belt or chain for stepless ratio change; DCT uses two clutches with separate odd and even gear shafts for fast shifts without torque interruption.

Propeller shaft needs universal joints for angle changes and a sliding spline for length variation; a worn UJ gives vibration that increases with speed.

Steering ratio = steering wheel rotation / road wheel rotation. Rack-and-pinion converts rotary input to linear rack movement; recirculating ball is used on heavier vehicles.

Ackermann principle: in a turn the inner road wheel must steer a larger angle than the outer because both turn about a common centre; incorrect geometry causes tyre scrub.

Wheel alignment angles: camber (in/out lean, affects tyre wear and directional pull), caster (steering axis tilt, gives self-centring), toe-in/toe-out (total toe measured in mm or degrees), steering axis inclination.

Caster positive gives straight-line stability; too little caster causes wander. Excessive negative camber wears the inner tyre edge; excessive positive camber wears the outer edge.

Suspension types: MacPherson strut, double wishbone, leaf spring (rigid axle, load carrying), coil spring with damper, torsion bar, air suspension. Spring carries load; damper (shock absorber) controls oscillation - a worn damper causes bounce and poor tyre contact.

Wheel balance: static imbalance gives vertical hop, dynamic imbalance gives wheel shimmy; corrected by clip-on or adhesive weights. Runout is measured with a dial gauge.

Power steering: hydraulic (pump, reservoir, rack valve) or electric (EPS motor and torque sensor). Symptoms: heavy steering - low fluid, slipping belt, failed pump or EPS fault; whine - low fluid or air in system.

Tyre marking example 165/70 R14: 165 = section width mm, 70 = aspect ratio %, R = radial, 14 = rim diameter inches. Tread wear indicators show the legal minimum depth.

Hydraulic braking works on Pascal's law: pressure is transmitted equally in all directions, so force at each wheel cylinder = pressure × piston area. Pedal force is multiplied by the pedal ratio and the master cylinder/slave cylinder area ratio.

Drum brake parts: brake drum, two shoes with linings, wheel cylinder, return springs, adjuster. Disc brake parts: disc (rotor), caliper, pads, piston. Discs cool better and resist fade; drums are self-energising and cheaper.

Brake fluid is hygroscopic; absorbed moisture lowers boiling point and causes vapour lock. DOT 3 and DOT 4 are glycol based and must not be mixed with DOT 5 silicone fluid.

Bleeding removes air from the hydraulic circuit, usually starting at the wheel farthest from the master cylinder. Spongy pedal = air in system; pedal slowly sinks to floor = internal master cylinder leak or external leak.

Parking brake acts mechanically on the rear wheels (cable and lever or electronic parking brake). It must hold the vehicle on a gradient with a defined lever travel.

ABS prevents wheel lock during hard braking by modulating pressure via solenoid valves and a pump, using wheel speed sensors; it retains steering control but does not necessarily shorten stopping distance on loose surfaces.

Braking distance depends on speed squared: doubling speed roughly quadruples the distance needed for the same deceleration. Reaction distance = speed × reaction time.

Brake faults: pull to one side (seized caliper, oil on lining, unequal adjustment), squeal (worn pads, glazed lining), vibration (warped disc, runout), drag (sticking caliper or collapsed hose).

Ohm's law V = I × R; power P = V × I = I²R = V²/R. A 12 V system with a 55 W lamp draws about 4.6 A.

Lead-acid battery: each cell about 2.1 V, so a 12 V battery has six cells. Capacity in Ah = current × time. Specific gravity of electrolyte falls as the battery discharges; check with a hydrometer.

Series circuits: same current, voltages add. Parallel circuits: same voltage, currents add. Vehicle loads are wired in parallel with the chassis as the earth return.

Starting system: battery → ignition switch → starter solenoid → starter motor. Voltage drop test on cables should be low (typically under 0.5 V per cable); clicking but no crank points to a flat battery, bad earth or solenoid.

Charging system: alternator with rectifier diodes and regulator, belt driven; warning lamp glows when output is below battery voltage. An alternator must never be run with the battery disconnected - voltage spikes destroy diodes.

Ignition: contact breaker and coil (older), electronic ignition, or coil-on-plug. Spark plug gap and heat range must match the engine; fouled plugs point to rich mixture or oil burning.

Lighting and accessories: headlamp circuits use relays to reduce switch current; fuses protect wiring, not components. A blown fuse should be replaced with the same rating, never a higher one or wire.

Sensors and electronics: ECU reads crank position, cam position, MAP/MAF, oxygen (lambda), coolant temperature, knock and throttle position. On-board diagnostics stores fault codes; a code identifies a circuit, not automatically the failed part.

Petrol fuel system: tank, fuel pump, filter, carburettor or fuel injection, air cleaner. Air-fuel ratio by mass: stoichiometric petrol about 14.7:1, diesel about 14.5:1; rich mixture = less air, lean = less fuel.

Diesel fuel system: tank, lift pump, fuel filter/water separator, injection pump or common rail, injectors. Diesel injection timing and atomisation control combustion noise and smoke.

Fuel faults: engine cranks but won't start - no fuel, no spark, or no compression; black smoke = over-rich or restricted air; blue smoke = oil burning; white smoke = coolant or unburnt diesel.

Lubrication system: sump, oil pump, oil filter, galleries, pressure relief valve. Oil functions: lubricate, cool, clean, seal, cushion and prevent corrosion.

SAE viscosity grade e.g. 15W-40: lower number = better cold flow (W = winter), higher number = thicker at operating temperature. API/ACEA service category must meet manufacturer requirement.

Oil pressure warning light on = stop the engine. Low pressure causes: low oil level, wrong grade, worn pump, blocked filter bypass, faulty sender, worn bearings.

Cooling system: radiator, water pump, thermostat, fan, hoses, expansion tank, coolant (antifreeze + water). Thermostat closed when cold for fast warm-up, opens at rated temperature.

Overheating causes: low coolant, slipping or broken fan belt, stuck-closed thermostat, blocked radiator, failed water pump, air lock. Coolant must not be opened hot - pressurised system can scald.

Periodic service items: engine oil and filter, air filter, fuel filter, spark plugs, brake inspection, tyre rotation and pressure, coolant, belts, battery terminals, suspension and steering check.

Daily/pre-start checks: engine oil level, coolant level, brake fluid, tyre condition and pressure, lights, horn, wipers, fuel level, leaks under the vehicle.

Tyre pressure is checked cold; under-inflation increases rolling resistance, heat and shoulder wear; over-inflation wears the centre tread. Rotate tyres to equalise wear.

Troubleshooting logic: confirm the complaint, gather symptoms, form a hypothesis, test the simplest and cheapest cause first, verify the repair. Use a systematic check - fuel, ignition/spark, compression for a no-start petrol engine.

Torque and fasteners: use a torque wrench for cylinder head, wheel nuts and suspension bolts; tighten in the specified sequence (usually spiral from centre outward for a head). Overtightening stretches bolts and warps parts.

Wheel nut tightening: tighten diagonally in stages to the specified torque; recheck after the first 50–100 km on a newly fitted wheel. Never lubricate threads unless specified.

Record keeping: service history, mileage, parts replaced and fault codes help diagnosis and resale. Warranty work must follow the manufacturer's schedule to remain valid.

Road test after repair: check brakes, steering, noises, warning lamps and fluid leaks before returning the vehicle; a repair is not complete until verified.

Measuring tools: vernier calliper (least count 0.02 mm typical), micrometer (0.01 mm), dial gauge (runout, end play), feeler gauge (valve clearance, plug gap), bore gauge (cylinder wear), torque wrench (fastener torque).

Vernier reading = main scale reading + (coinciding vernier division × least count). Micrometer reading = barrel reading + thimble reading × 0.01 mm.

Hand tools: spanners (open-end, ring, combination), sockets and ratchet, Allen keys, screwdrivers, pliers, hammers, chisels, punches, taps and dies, pullers. Use the correct size to avoid rounding nuts.

Lifting and holding: engine crane, chain block, trolley jack, axle stands, vice, clamps. Never work under a vehicle held only by a jack; use stands on firm level ground.

Cutting and finishing: hacksaw blade teeth per inch chosen for material, files for finishing, bench grinder for tool sharpening, drill with correct speed and lubrication; wear goggles for all of these.

Fastener and thread terms: pitch, major/minor diameter, right-hand and left-hand thread, torque-to-yield bolts, locking devices (split pin, tab washer, thread-locking compound, nyloc nut).

Cleaning and inspection: degrease parts before inspection, check for cracks with dye penetrant or magnetic particle methods, measure wear against the manufacturer's limit rather than judging by eye.

Workshop organisation: 5S-style housekeeping (sort, set in order, shine, standardise, sustain), correct waste segregation for oil, coolant, batteries and tyres, and a fire extinguisher within reach of the work area.