UPMSP Vocational Automobile cheat sheet

Chassis layout terms: engine at front driving rear wheels = FR; engine front driving front wheels = FF; engine rear driving rear wheels = RR; engine front driving all four wheels = 4WD/AWD.

Main vehicle subsystems: engine (power plant), transmission/drivetrain (torque delivery), running gear (suspension, wheels, tyres), braking system, steering system, and electrical system.

Fire classes for workshop use: Class A solid combustibles (water/foam), Class B flammable liquids (foam, dry powder, CO2), Class C gases, Class D metals, and electrical fires (CO2 or dry powder only, never water).

Safe jacking rule: jack only under manufacturer-specified lift points on the chassis/axle; always place axle stands before working under a raised vehicle; never rely on the hydraulic jack alone.

Personal protective equipment in an auto workshop: safety goggles when grinding or using compressed air, gloves for chemicals and hot parts, steel-toe boots, and ear protection above roughly 85 dB.

Battery safety: lead-acid batteries release hydrogen during charging; keep sparks and open flames away, ventilate the area, and disconnect the negative (earth) terminal first and reconnect it last.

Lifting formula: mechanical advantage of a pulley/lever system = load divided by effort; a hydraulic jack obeys Pascal's law, pressure transmitted equally, force = pressure x piston area.

Hand tool rules: spanners must fit the fastener exactly (metric vs imperial, six-point for rounded nuts); never extend a spanner with a pipe to increase leverage; pull rather than push a wrench where possible.

First aid basics: for acid on skin, flush with plenty of clean water for at least 15 minutes; for eye splashes, irrigate from the inner to the outer corner and seek medical help.

Four-stroke cycle order: intake, compression, power (expansion), exhaust; the crankshaft completes two revolutions (720 degrees) per cycle, and the camshaft turns once (2:1 reduction).

Compression ratio = (swept volume + clearance volume) / clearance volume; petrol engines typically 8:1 to 12:1, diesel 16:1 to 23:1.

Engine capacity (cc) = (pi/4) x bore squared x stroke x number of cylinders, with bore and stroke in cm to get cc directly.

Valve timing terms: TDC and BDC; valve overlap is the period when both intake and exhaust valves are open around TDC of the exhaust stroke; valve clearance is set cold for most engines.

Firing order examples: 4-cylinder in-line 1-3-4-2; 6-cylinder in-line 1-5-3-6-2-4; V8 commonly 1-8-4-3-6-5-7-2. Firing order balances loads on the crankshaft.

Diesel combustion needs high compression to raise air temperature above the fuel's ignition point; a glow plug assists cold starting in indirect-injection diesels.

Turbocharger vs supercharger: turbo is driven by exhaust gas (lag, heat issues), supercharger is mechanically belt/gear driven (immediate response, parasitic loss).

Torque and power relation: Power (kW) = Torque (N.m) x angular speed (rad/s); in common units, Power (kW) approximately equals Torque (N.m) x rpm / 9549.

Manual gearbox gear ratio = driven gear teeth / driving gear teeth; overall ratio = gearbox ratio x final drive ratio; lower ratio number means higher vehicle speed for a given engine speed.

Clutch operation: the pressure plate clamps the friction disc to the flywheel; pressing the pedal releases clamping force; free play at the pedal is typically 10-25 mm and must allow full engagement.

Synchromesh uses a cone clutch to equalize shaft speeds before dog teeth engage, preventing gear clash; it works on the gear being selected, not on reverse in most designs.

Automatic transmission main parts: torque converter (fluid coupling with stator), planetary gear sets, hydraulic valve body, and bands/clutches; the stator multiplies torque at low speed.

CVT transmits power through a steel belt or chain between two variable-diameter pulleys; ratio changes continuously, so no fixed gear steps.

Differential function: allows inner and outer wheels to rotate at different speeds during a turn while still delivering torque; crown wheel to pinion ratio is the final drive ratio.

Limited-slip differential (LSD) limits speed difference by clutch packs or a viscous coupling, improving traction when one wheel loses grip.

Propshaft and universal joints transmit torque between gearbox and final drive; a two-piece shaft needs a centre bearing, and joints must be phased to avoid vibration.

Transfer case in 4WD splits drive to front and rear axles; part-time 4WD must not be used on dry hard surfaces because there is no centre differential to absorb wind-up.

Hydraulic brake principle: Pascal's law; pedal force multiplied by pedal ratio and by the ratio of master cylinder area to wheel cylinder/caliper piston area gives braking force.

Disc brake advantages over drum: better heat dissipation, self-adjusting, less fade, easier pad replacement; drum brakes use a self-energizing leading shoe effect.

Brake fluid DOT 3/4 are glycol-based and hygroscopic (absorb moisture); DOT 5 is silicone-based and must not be mixed with glycol fluid; boiling fluid causes brake fade.

ABS prevents wheel lock by modulating pressure; it does not shorten stopping distance on all surfaces but preserves steering control during hard braking.

Steering geometry: camber (wheel tilt from vertical), caster (steering axis tilt giving self-centring), toe-in/toe-out (front edge distance difference), and kingpin inclination (SAI).

Ackermann principle: the inner wheel turns through a larger angle than the outer wheel so all wheels roll around a common centre, minimizing tyre scrub.

Rack-and-pinion converts rotary steering wheel motion to linear tie-rod movement; recirculating-ball steering is used on heavier vehicles for lower effort.

Suspension parts: springs (coil, leaf, torsion bar, air), shock absorbers (damp oscillations), control arms, ball joints, and anti-roll bar (reduces body roll).

Wheel alignment symptoms: uneven tyre wear on one edge indicates camber or toe error; pull to one side suggests caster or camber imbalance or a dragging brake.

Ohm's law: V = I x R; power P = V x I = I squared x R = V squared / R; used to size fuses, wires, and diagnose voltage drops.

Series circuit: current is the same through all components, voltages add; parallel circuit: voltage is the same across branches, currents add; vehicle loads are wired in parallel.

Battery capacity: ampere-hour (Ah) rating and cold cranking amps (CCA); a 12 V lead-acid battery has six cells of about 2.1 V each in series.

Charging system: alternator converts rotation to AC then rectifies to DC via diodes; a voltage regulator holds roughly 13.8-14.5 V; a warning lamp glows if output is low.

Starter motor draws high current (often 100-300 A); a clicking starter usually indicates low battery charge, poor earth strap, or faulty solenoid contacts.

Ignition coil steps 12 V up to thousands of volts; spark plug gap is typically 0.7-1.1 mm; incorrect heat range causes fouling (too cold) or pre-ignition (too hot).

Multimeter use: voltage measured in parallel across a load, current in series, resistance with the circuit de-energized; a voltage drop above 0.5 V on a cable indicates high resistance.

CAN bus is a twisted-pair serial network where modules exchange data; a shorted CAN line or missing terminating resistance can disable many electronic functions at once.

Fuses protect wiring, not components; replace a blown fuse with the same rating only, and find the cause before replacement.

Stoichiometric air-fuel ratio: about 14.7:1 by mass for petrol and about 14.5:1 for diesel; rich mixture = excess fuel, lean = excess air.

Fuel system parts: tank, fuel pump (mechanical or electric), filter, carburettor or fuel injection, and return line; EFI uses an ECU to control injector pulse width.

Diesel fuel injection needs high pressure (common rail can exceed 1000 bar) and precise timing; air in the fuel line causes hard starting and requires bleeding.

Engine oil functions: lubricate, cool, clean, seal, and protect against corrosion; viscosity grade like 10W-40 means winter grade 10 and hot grade 40 (higher number = thicker).

Oil change interval depends on oil type and use; check level with the dipstick on level ground with the engine off, and never overfill (foaming and seal damage).

Cooling system: water pump circulates coolant, thermostat regulates flow to maintain about 80-95 degrees C, radiator dissipates heat, pressure cap raises boiling point.

Coolant is an antifreeze/water mix (often 50:50) that lowers freezing point and raises boiling point; never open a hot radiator cap because pressurized coolant can flash to steam.

Overheating causes: low coolant, faulty thermostat, failed water pump, blocked radiator, slipping fan belt, or head gasket failure (white exhaust smoke, coolant loss).

Periodic service items: engine oil and filter, air filter, fuel filter, spark plugs, brake fluid, coolant, tyre rotation, and inspection of belts, hoses, and suspension.

Tyre maintenance: check pressure cold; tread wear indicator at 1.6 mm minimum; rotate tyres to equalize wear; imbalance causes vibration, misalignment causes uneven wear.

Diagnostic sequence: verify the complaint, gather information, inspect visually, test with instruments, isolate the fault, repair, then verify the repair and clear codes.

OBD-II stores diagnostic trouble codes (DTCs); a code identifies a circuit or system, not necessarily the failed part, so follow the pinpoint test before replacing components.

Compression test identifies worn rings, valves, or head gasket; a wet test (adding oil) raising compression indicates worn piston rings.

Battery test: open-circuit voltage about 12.6 V at full charge, 12.0 V around 50 percent; a load test or conductance test confirms cranking ability.

Brake inspection: minimum pad friction material thickness and disc run-out; check for scoring, fluid leaks at calipers, and correct pedal free play.

Road test checks for noises, vibration, pulling, and gearshift quality; record speed and conditions so faults can be reproduced.

Body construction types: separate chassis with body on frame (commercial vehicles, off-roaders) and unitary/monocoque body (most passenger cars) where the body carries structural loads.

Crumple zones absorb impact energy by controlled deformation; the passenger safety cell is reinforced to resist deformation and protect occupants.

Panel repair steps: assess damage, remove trim, straighten with dolly and hammer or pull with a frame machine, apply body filler, sand, prime, then paint.

Paint system layers: bare metal, primer (adhesion and corrosion protection), base coat (colour), and clear coat (gloss and UV protection); each layer must cure before the next.

Surface preparation is critical: degrease, sand to the correct grit, and mask properly; contamination causes fisheyes, peeling, and poor adhesion.

Paint defects: runs (too much material), orange peel (incorrect spray pressure or viscosity), blistering (moisture under the film), and fading (UV or thin clear coat).

Welding and joining in body repair: MIG welding for steel panels, spot welding for factory joints, and adhesive bonding or rivets for aluminium and mixed-material bodies.

Chassis alignment: check frame dimensions against manufacturer data after a collision; suspension mounting points and wheel alignment must be restored before cosmetic repair.

Measurement tools: vernier calliper (0.02 mm resolution typical), micrometer (0.01 mm), dial gauge (run-out and end play), feeler gauge (clearances), and torque wrench (fastener tightening to specification).

Torque wrench use: set the specified value, tighten in the specified sequence (often spiral from centre outward for cylinder heads), and never use a torque wrench to loosen fasteners.

Thread standards: metric coarse and fine, and imperial UNC/UNF; a bolt must match the thread pitch and grade of the hole; grade markings (e.g. 8.8, 10.9) indicate tensile strength.

Tap and die use: tap cuts internal threads, die cuts external threads; use the correct drill size for a tap (drill diameter approximately equals nominal diameter minus pitch) and lubricate while cutting.

Precision limits: cylinder bore wear is measured with a bore gauge; taper and ovality limits are given by the manufacturer; honing restores crosshatch for oil retention.

Fastener removal: penetrating oil and heat help free rusted bolts; use a six-point socket for rounded heads; never use an impact gun on a torque-critical fastener unless specified.

Hand tool care and identification: spanners (open-end, ring, combination), sockets (six- and twelve-point), screwdrivers (flat, Phillips, Pozidriv), pliers, and hacksaws; keep cutting edges sharp.

Lifting and supporting loads: use rated lifting equipment, keep the load close to the body, and never exceed the safe working load marked on slings and jacks.