NSSCO Motor Mechanics 6189 cheat sheet

Fire triangle: fuel + oxygen + ignition source; removal of any one leg extinguishes combustion. Class A = solids (water), B = flammable liquids (foam/CO2/dry powder), C = gases, D = metals (dry powder), electrical = CO2 or dry powder only.

COSHH hierarchy of control: eliminate > substitute > engineering controls (LEV) > administrative controls > PPE last. Safety data sheets (SDS) supply hazard, exposure limits and first-aid data.

Petrol flash point approx -43 °C, auto-ignition approx 250-280 °C; petrol vapour is heavier than air and collects at floor level. Diesel flash point approx 52-60 °C.

Battery charging releases hydrogen; explosive range in air approx 4-75 % by volume. Charge in ventilated areas, no naked flame, remove metal jewellery, connect positive last and disconnect negative first.

Exhaust carbon monoxide is colourless and odourless; binds haemoglobin roughly 200-250 times more strongly than oxygen. Never run engines in enclosed spaces without extraction.

Coolant containing ethylene glycol is toxic and sweet-tasting; collect in labelled containers, never drain to ground or drain. Waste oil, filters, batteries and tyres are controlled waste requiring licensed disposal.

Lifting rule: keep the load close to the body, back straight, lift with legs, no twisting under load. Two-person or mechanical lift above approx 25 kg. Jacks must be supplemented by axle stands before working under a vehicle.

Noise action values (daily exposure): lower 80 dB(A) - hearing protection available on request; upper 85 dB(A) - protection mandatory and hearing surveillance required.

Compressed air must never be used to clean skin or clothing; limit for blow-gun nozzles is typically 2 bar (30 psi) with chip guards and eye protection.

Micrometer reading = main barrel scale + thimble scale × least count. Metric least count 0.01 mm (thimble 50 divisions over 0.5 mm); imperial 0.001 in (thimble 25 divisions over 0.025 in).

Vernier caliper: reading = main scale value + (coinciding vernier division × least count). Least count = 1 main division / number of vernier divisions, e.g. 1 mm / 20 = 0.05 mm; 1 mm / 50 = 0.02 mm.

Dial test indicator (DTI) measures small displacements, runout and backlash; dial gauge (plunger type) measures comparative height or end float. Both require a magnetic base or stand and zeroing against a datum.

Torque wrench types: click (set value, release after one click), beam/deflection (direct reading, no setting), electronic. Calibration interval typically 12 months or 5,000 cycles; never use a torque wrench to loosen fasteners.

Feeler gauge measures valve clearance, ring end gap and spark plug gap by stacking blades; plastigauge measures bearing oil clearance by crushing a calibrated plastic strip and comparing width to scale.

Bore gauge (inside micrometer or dial type) is set against a micrometer, then read in the cylinder at top, middle and bottom, in two planes at 90° to check taper and ovality.

Six-point sockets contact flats and resist rounding; 12-point suit square or bi-hex fasteners. Impact sockets are chrome-molybdenum, hand sockets chrome-vanadium; never use hand sockets on impact tools.

Tap drill size = nominal thread diameter − thread pitch (metric coarse). Example: M10 × 1.5 needs a 8.5 mm drill; M8 × 1.25 needs 6.75 mm (use 6.8 mm).

Four-stroke cycle = 720° crankshaft rotation: induction (180°), compression (180°), power/expansion (180°), exhaust (180°). Two-stroke cycle completes in 360° with transfer and exhaust ports uncovered by piston travel.

Compression ratio CR = (swept volume + clearance volume) / clearance volume = (Vs + Vc) / Vc. Petrol spark-ignition typically 8:1 to 12:1; diesel compression-ignition typically 16:1 to 23:1.

Swept volume of one cylinder Vs = (π/4) × bore² × stroke. Engine capacity = Vs × number of cylinders. Example: 80 mm bore, 90 mm stroke = 0.7854 × 6400 × 90 = 452,389 mm³ ≈ 452 cm³.

Valve timing: inlet opens before TDC and closes after BDC (inertia ram effect); exhaust opens before BDC and closes after TDC (overlap). Overlap improves scavenging but increases hydrocarbon emissions at idle.

Firing order distributes power strokes: in-line four commonly 1-3-4-2; in-line six commonly 1-5-3-6-2-4. Firing interval = 720° / number of cylinders for a four-stroke.

Two-stroke crankcase-scavenged engines use piston-port, reed-valve or rotary-valve induction; mixture is petrol plus oil (commonly 1:50 or 2 %), since lubrication comes from the fuel charge, not a sump.

Diesel ignition occurs by heat of compression; glow plugs assist cold starting on indirect-injection engines, whereas direct-injection engines rely on high compression and precise injector timing.

Volumetric efficiency = actual air mass inducted / theoretical swept-volume air mass. Boost pressure from a turbocharger raises it above 100 %; valve size, port design and cam profile set its limit.

Cylinder block materials: cast iron (wear resistant, heavy) or aluminium alloy with pressed-in or cast-in liners. Liner types: dry (not in contact with coolant) and wet (coolant contacts liner; sealed by O-rings at top and bottom).

Piston clearance measured at the skirt, 90° to the gudgeon pin axis, using a micrometer and bore gauge. Ring end gap measured with the ring squared in the bore by a piston; typical top-ring gap approx 0.003-0.004 × bore in mm.

Ring set: top compression ring (often chrome or moly faced, barrel-faced), second compression ring (taper-faced scraper), oil control ring (three-piece with expander). Ring gaps must be staggered on assembly.

Crankshaft: main and big-end journals ground to standard undersizes (e.g. 0.25 mm, 0.50 mm); check with micrometer for taper and ovality (limit commonly 0.02-0.05 mm) and check runout at the centre main.

Torque-to-yield (TTY) head bolts must be replaced after use; tighten in the specified sequence (spiral from centre outward) to a torque angle, e.g. 40 N·m + 90° + 90°. Reused bolts lose clamping load.

Valve clearance (lash) is set cold or hot per specification; too little clearance causes valve not to seat (burning, compression loss), too much causes noise, reduced lift and wear on cam and follower.

Cylinder head warpage checked with a straight edge and feeler gauge across diagonals and along the length; typical limit 0.05 mm over 150 mm. Skimming changes compression ratio and valve timing slightly.

Bearing shells: check oil clearance with plastigauge, check for scoring, pitting and copper backing exposure. Crankshaft end float measured with a DTI against the thrust face; typical limit 0.10-0.30 mm.

Oil grades: SAE viscosity e.g. 10W-40 means cold-crank viscosity grade 10W and hot (100 °C) grade 40. API/ACEA service categories define performance, not viscosity. Multigrade oils use viscosity-index improvers.

Full-flow oil filter is in series and filters all oil; bypass filter takes a small bleed. Bypass valve in the filter or block opens when the element is blocked, maintaining flow with unfiltered oil.

Oil pressure warning lamp switch closes at low pressure (typically 0.2-0.5 bar); gauge sender is a variable resistance. Low pressure causes: low level, wrong grade, worn pump, blocked pickup, worn bearings.

Cooling system: pressurised to raise boiling point, roughly +3 °C per 0.1 bar above atmospheric (1 bar cap ≈ 120 °C with glycol mix). Thermostat opens typically 82-90 °C and controls warm-up.

Coolant flow: water pump → block → head → thermostat → radiator → back to pump. Heater matrix is a parallel branch. Air lock causes overheating and no heater output; bleed at the highest point.

Fuel system: petrol port injection delivers fuel at approx 3-4 bar, direct injection 50-200 bar, common-rail diesel 1,500-2,500 bar. Fuel filter water separators on diesel must be drained regularly.

Stoichiometric air-fuel ratio: petrol approx 14.7:1 by mass; diesel approx 14.5:1. Rich mixture (lambda < 1) increases CO and HC; lean mixture increases NOx and can cause misfire.

Three-way catalytic converter controls CO, HC and NOx only near lambda = 1; it needs closed-loop lambda sensor control. Diesel uses oxidation catalyst, DPF and often SCR with AdBlue (urea).

Ohm's law V = I × R; power P = V × I = I²R = V²/R. Example: 55 W headlamp at 12 V draws 4.58 A and has 2.62 Ω resistance when hot.

Series circuit: same current, voltages add, total R = R1 + R2. Parallel circuit: same voltage, currents add, 1/RT = 1/R1 + 1/R2. Vehicle loads are wired in parallel.

Lead-acid cell nominal 2.1 V; six cells give 12.6 V at rest. State of charge from open-circuit voltage: 12.6 V = 100 %, 12.4 V ≈ 75 %, 12.2 V ≈ 50 %, 12.0 V ≈ 25 %.

Specific gravity of electrolyte indicates charge: approx 1.265 fully charged, 1.150 discharged, corrected by 0.004 per 10 °C from 25 °C. Maintenance-free batteries cannot be checked this way.

Alternator output is three-phase rectified by six diodes; ripple or low output indicates a failed diode. Charge voltage typically 13.8-14.4 V; below 13.5 V at speed indicates fault.

Starter motor is a series-wound DC motor with a Bendix or pre-engaged solenoid drive. High current draw with slow cranking suggests seized engine, faulty earth strap or worn brushes; clicking suggests solenoid or low battery.

Voltage drop testing: measure volts across the cable or connection under load; limit typically 0.2 V per connection and 0.5 V total on the earth return. Clean and tighten rather than replace parts.

Cranking circuit: battery → positive cable → solenoid → starter → engine block → earth strap → battery negative. Every joint is a potential high-resistance fault.

Manual clutch: flywheel, driven plate, pressure plate, release bearing, release fork. Free play at the pedal (typically 10-25 mm) prevents release bearing from spinning continuously.

Clutch slip symptoms: engine speed rises without road speed, burning smell. Clutch drag (not releasing) causes difficult gear engagement and creeping; check hydraulics, cable adjustment and plate distortion.

Gear ratio = driven gear teeth / driving gear teeth. Overall ratio = gearbox ratio × final drive ratio. Road speed (km/h) = (engine rpm × 60 × rolling circumference in m) / (overall ratio × 1000).

Manual gearbox uses constant-mesh gears with synchromesh cones; baulk ring friction matches shaft speeds before dog engagement. Automatic uses planetary gearsets with clutches and bands.

Final drive ratio = crown wheel teeth / pinion teeth. Hypoid gears require special EP (extreme pressure) oil; the pinion offset below the crown wheel centreline is a hypoid characteristic.

Differential gear ratio and action: when the vehicle turns, the average of the two wheel speeds equals the crown wheel speed; the planet gears allow inner and outer wheels to rotate at different speeds.

Limited-slip differential uses clutch packs, viscous coupling or Torsen gears to limit speed difference; it needs the specified LSD additive or dedicated lubricant to avoid chatter.

Backlash and preload: crown wheel backlash typically 0.10-0.20 mm, measured with a DTI; pinion preload is set with crush collars or shims and measured by turning torque.

Wheel alignment angles: camber (vertical tilt, typically 0-1° negative), caster (steering axis tilt, gives self-centring), toe (difference in track front to rear, typically 0-3 mm total toe-in), steering axis inclination (SAI) and included angle.

Ackermann principle: inner wheel steers at a larger angle than the outer wheel because the steering arms point toward the rear axle centre, allowing all wheels to roll without scrub on a turn.

Rack-and-pinion ratio gives turns lock-to-lock; excessive free play at the steering wheel (typically over 25-30 mm) indicates worn rack, track rod ends or column joints.

Tyre markings: e.g. 195/65 R15 91H means section width 195 mm, aspect ratio 65 %, radial, rim diameter 15 in, load index 91, speed rating H. Aspect ratio = sidewall height / section width × 100.

Tyre pressures set cold; pressure rises approx 0.1 bar per 10 °C. Underinflation increases rolling resistance, shoulder wear and heat; overinflation causes centre wear and reduced grip.

Wear patterns: both shoulders worn = underinflation; centre worn = overinflation; one shoulder = camber or toe fault; feathered tread = incorrect toe; cupping/scalloping = worn dampers or imbalance.

Suspension types: MacPherson strut (combined damper and spring, locates wheel), double wishbone (independent, good camber control), torsion bar, leaf spring (beam axle, load carrying), trailing arm.

Wheel balance: static imbalance causes vertical shake (bounce), dynamic imbalance causes wheel shimmy (side-to-side). Balance weights measured in grams; runout checked with a DTI on the rim.

Hydraulic braking follows Pascal's law: pressure is equal throughout a confined fluid. Force = pressure × area, so a larger wheel-cylinder or caliper piston area gives greater clamping force.

Pedal ratio = pedal travel / master-cylinder pushrod travel; typical 4:1 to 6:1. Pedal effort multiplied by ratio and by the servo assistance gives the line pressure.

Brake fluid DOT 3 and DOT 4 are glycol-based and hygroscopic; DOT 5 is silicone-based (not hygroscopic, not mixable). Wet boiling point falls as water content rises; fluid change typically every 2 years.

Disc brake: pads squeeze a rotating disc; heat dissipation is good but no self-servo action. Drum brake: shoes expand against a rotating drum, self-servo increases force but fade and adjustment are issues.

Brake fade is loss of friction from heat (discs, pads) or from vapour lock in the hydraulic fluid. Fade recovery after cooling; vapour lock requires bleeding and fresh fluid.

ABS prevents wheel lock by modulating pressure via solenoid valves, monitoring wheel speed sensors. Typical fault: sensor air gap, damaged reluctor ring, wiring, or low fluid.

Parking brake is mechanical (cable or electronic) acting on rear wheels; typical adjustment leaves 3-6 clicks of travel. It must hold the vehicle on a specified gradient.

Brake test: rolling road or decelerometer; imbalance between wheels on the same axle should not exceed a specified percentage (often 30 % for service brake).

Chassis types: ladder frame (body-on-frame, load carrying), monocoque/unibody (body and chassis combined, lighter and stiffer), space frame and tubular frame. Monocoque repairs require panel alignment and corrosion protection.

Corrosion protection: galvanising, electrophoretic coating (e-coat), seam sealer, cavity wax and underseal. Repair welds must be primed and sealed; bare steel rusts quickly in humid conditions.

Service schedule items: engine oil and filter, air filter, fuel filter, brake fluid, coolant, spark plugs, belts, tyre pressures and tread depth (legal minimum commonly 1.6 mm across the central 3/4 of the tread).

Pre-delivery and periodic inspection: check fluid levels, belt tension and condition, brake pad thickness, tyre condition, lighting, wipers, battery terminals, suspension play and exhaust integrity.

Panel repair: filler must be applied to bare, abraded metal; primer then topcoat. Paint thickness measured in micrometres; excessive thickness indicates previous repair.

Body measurement uses datum points and a jig or measuring system; allowable deviation is small, typically a few millimetres. Structural damage affects wheel alignment and crash performance.

Lubrication points and greasing: ball joints, track rod ends, propshaft U-joints (where nipples exist) require the specified grease. Sealed-for-life components must not be greased.

Vehicle lifting and support: use manufacturer jacking points only; support on axle stands at the chassis or subframe. Never work under a vehicle supported only by a jack.

Area and volume: circle area = πr² = (π/4)d²; cylinder volume = πr²h; rectangle area = l × w. Use consistent units; 1 cm³ = 1 mL, 1 litre = 1,000 cm³.

Unit conversions: 1 inch = 25.4 mm; 1 mm = 0.03937 in; 1 bar = 100 kPa = 14.5 psi; 1 N·m = 0.7376 lbf·ft; 1 kgf = 9.81 N; 1 hp = 0.746 kW.

Percentage and ratio: percentage = (part / whole) × 100. Ratio simplification by dividing both terms by their greatest common divisor. Mixture ratio 1:50 means 1 part oil to 50 parts petrol, i.e. 20 mL oil per litre.

Mechanical advantage = load / effort; velocity ratio = distance moved by effort / distance moved by load; efficiency = (mechanical advantage / velocity ratio) × 100 %.

Gear and pulley calculations: speed ratio = product of driven teeth / product of driving teeth. Belt speed = π × pulley diameter × rpm / 60 (in m/s when diameter is in metres).

Technical drawing conventions: first-angle projection (view from front placed behind, top view below) versus third-angle (top view above). Hidden detail = dashed lines; centre lines = long-short dashes.

Dimensioning: dimensions in millimetres unless otherwise stated; tolerances shown as limits or as ± value; fits described as clearance, transition or interference. Surface finish symbol in micrometres (Ra).

Scale drawing: scale 1:2 means drawing is half size; 2:1 means twice size. Calculate the actual dimension by multiplying the drawing dimension by the scale denominator.

Risk assessment steps: identify hazards, decide who may be harmed and how, evaluate risks and controls, record findings, review and update. Risk = likelihood × severity.

Personal protective equipment: safety footwear (toe cap), eye protection for grinding and compressed air, gloves for chemicals (not for rotating machinery), hearing protection, respirator for paint and solvents.

Machine guarding: abrasive wheel guard covers the wheel except the working arc; tool rest set within 2 mm of the wheel; ring test a vitrified wheel before mounting to detect cracks.

Manual handling and lifting equipment: inspect slings, chains and shackles before use; never exceed safe working load (SWL). Jacks and hoists need periodic examination and certification.

Electrical safety in the workshop: RCD protection on portable tools, 110 V centre-tapped-to-earth for site use, no damaged leads, no water near electrical equipment, lock off before repair.

Spill response: absorbent granules or pads for oil and fuel, contain and prevent entry to drains, dispose as hazardous waste. Do not wash spills into drains with water.

Environmental controls: bunded storage for oils and chemicals, drip trays under vehicles, extraction for paint and welding fume, correct segregation of waste oil, filters, batteries, tyres and solvents.

First aid and emergency: eyewash station for chemical splash, burns treatment (cool with water, do not remove adherent clothing), fire extinguisher selection by class, clear escape routes and assembly point.

Measuring bore wear: use a bore gauge set with a micrometer at three heights and two planes (thrust and axial). Taper = difference between top and bottom readings; ovality = difference between the two planes.

Piston-to-bore clearance: measure piston skirt diameter at 90° to the gudgeon pin, subtract from bore diameter. Too little clearance causes seizure; too much causes piston slap and oil consumption.

Crankshaft journal measurement: micrometer across two planes at each end and centre of each journal. Regrind to the next undersize if taper or ovality exceeds the limit; then fit matching undersize bearings.

Valve guide wear: measure guide bore with a small-hole gauge and valve stem with a micrometer; clearance limit typically 0.05-0.10 mm for inlet, slightly more for exhaust. Excessive wear causes oil burning and poor seating.

Valve seat width: typically 1.5-2.0 mm for inlet and exhaust; too wide reduces sealing pressure, too narrow causes rapid wear and overheating. Cut at the specified angle (often 45° or 30°).

Camshaft check: lobe lift measured with a micrometer or DTI; base-circle runout and journal wear checked. Worn lobes reduce valve lift and alter timing.

Timing belt/chain alignment: align marks on crank, cam and (where fitted) injection pump before removing the belt. Rotate two full turns after fitting and re-check marks and tension.

Torque and sequence: cylinder head bolts tightened in a spiral from the centre outward in stages to the specified torque or torque angle; main bearing caps from centre outward. Never reuse TTY bolts or distorted gaskets.

Multimeter use: volts across a load (parallel), amps in series (or clamp meter), ohms with circuit isolated and power off. Continuity test for opens; resistance test for expected values.

Voltage drop method: connect voltmeter across the cable or joint while the circuit is loaded; a reading above approx 0.2 V per connection indicates excessive resistance. This is more reliable than an ohmmeter for high-current circuits.

Parasitic drain test: measure current with everything off, typically below 50 mA (0.05 A) after modules sleep. Higher values indicate a faulty module, lamp or alternator diode.

Alternator test: engine running, measure battery voltage (13.8-14.4 V) and AC ripple (should be below approx 0.5 V AC). High ripple indicates a failed rectifier diode.

Starter circuit test: measure battery voltage during cranking (should stay above approx 9.5-10 V); if low, test battery capacity and cables. High current draw with slow cranking suggests mechanical seizure.

Sensor testing: inductive crank/cam sensors produce an AC signal; Hall-effect sensors switch a square wave. Check supply, earth and signal with a multimeter or oscilloscope.

Relay and fuse diagnosis: a fuse blown indicates a short or overload - find the cause before replacing. Test relay by checking coil resistance and contact continuity when energised.

CAN bus basics: two twisted wires, CAN-High and CAN-Low, with terminating resistors (typically 120 Ω each, 60 Ω measured across the pair). A short or open bus stops communication.

Clutch diagnosis: slip under load (worn plate, oil contamination, weak diaphragm spring), judder (oil on plate, warped flywheel, worn mounts), noise on pedal press (release bearing), noise with pedal released (gearbox input bearing).

Manual gearbox noise: whine in one gear only suggests that gear pair; noise in all gears suggests input or output shaft bearings; noise in neutral with clutch engaged suggests input shaft bearing.

Gear selection faults: difficulty engaging gears with engine running but easy with engine off suggests clutch drag. Jumping out of gear suggests worn detents, selector forks or synchromesh.

Automatic transmission checks: fluid level and condition (burnt smell, dark colour indicates overheating), stall test, line pressure test, and road test for shift quality and slip.

Propshaft and CV joints: vibration at speed suggests imbalance or worn U-joints; clicking on full lock suggests worn outer CV joint; vibration under acceleration suggests inner CV joint or centre bearing.

Differential diagnosis: whine on acceleration followed by quiet on overrun suggests pinion/ring gear wear; noise on turns suggests side gear or limited-slip clutch wear; leaks at pinion or side seals.

Wheel bearing test: raise and spin the wheel, check for roughness and play at 12-6 o'clock and 3-9 o'clock; noise that changes with cornering load indicates a wheel bearing.

Lubricant specification: manual gearboxes use GL-4 or GL-5 as specified; hypoid final drives require GL-5 EP oil; automatic transmissions require the manufacturer's specific ATF. Wrong oil causes shift or wear problems.

Steering pull to one side: check tyre pressures and sizes, uneven tyre wear, dragging brake, wheel alignment (camber and caster), and worn suspension bushes.

Vibration in steering wheel at a specific speed: wheel balance, tyre runout, bent rim, worn track rod ends or worn steering rack. Vibration under braking suggests warped discs.

Wandering or vague steering: excessive free play, worn rack, worn track rod ends, worn suspension bushes, incorrect toe or caster. Check all joints before adjusting alignment.

Suspension noise over bumps: worn anti-roll bar bushes and links, worn strut top mounts, worn ball joints, worn shock absorbers (bounce test - more than one rebound indicates worn damper).

Tyre wear diagnosis: inner or outer edge wear = camber or toe; feathered tread = toe; cupping = imbalance or worn dampers; flat spots = locked brakes or out-of-balance.

Wheel alignment procedure: set tyre pressures, check ride height and play, then measure camber, caster and toe; adjust toe last. Steering wheel centred before adjustment.

Run-flat and low-profile tyres: stiffer sidewalls, may require specific equipment for mounting; run-flats limited to approx 80 km at 80 km/h after pressure loss.

TPMS: direct system uses wheel sensors with batteries (life approx 5-10 years); indirect uses ABS wheel speed sensors to detect pressure loss from rolling radius changes.

Spongy pedal: air in hydraulic system, faulty master cylinder seals, flexible hose swelling, or low fluid. Bleed in the specified sequence, usually furthest from the master cylinder first.

Pedal sinks slowly under steady pressure: internal master-cylinder seal leak (bypassing). Pedal goes to floor: fluid loss, failed seal or broken line. Check for leaks at all joints.

Brake pull to one side: seized caliper or wheel cylinder, contaminated or glazed pads/shoes, collapsed flexible hose, or uneven pad wear. Compare both sides.

Brake noise: squeal from pad vibration (fit anti-squeal shims or grease), grinding from worn pads metal-to-metal, click from worn pad retainers.

Brake judder: disc thickness variation (DTV), warped disc, worn wheel bearings, or loose caliper. Measure disc thickness and runout with a micrometer and DTI.

Handbrake adjustment: cable type - adjust at the equaliser until 3-6 clicks; electronic - use the diagnostic routine. Check rear brake shoe or caliper operation first.

Brake fluid service: flush and replace every 2 years typically; bleed until clean fluid appears at each bleeder; never reuse fluid. Keep fluid away from paint.

ABS warning lamp: check wheel speed sensors, reluctor rings, wiring and fuses; scan for fault codes. The base brake system remains functional but without anti-lock control.

Service intervals are set by time or distance, whichever comes first. Severe-duty schedules (short trips, dusty, towing) shorten oil and filter intervals.

Fluid checks: engine oil (level and condition), coolant (level and strength, typically 50 % glycol), brake fluid (level and moisture), transmission fluid, power steering fluid, washer fluid, battery electrolyte.

Belt inspection: check for cracks, glazing, fraying and correct tension. A squealing belt suggests low tension or misalignment. Replace serpentine belts as a set with tensioner if worn.

Brake and tyre inspection: pad thickness (replace at approx 2-3 mm), disc thickness against minimum, tyre tread depth and sidewall condition, tyre pressures including spare.

Bodywork repair sequence: strip, clean, assess damage, straighten or replace panels, apply primer, filler, primer surfacer, topcoat and clear coat. Corrosion protection applied to cavities and seams.

Paint defects: runs (too much material), orange peel (spray too dry or too fast), blistering (moisture or contamination), fisheyes (silicone contamination). Preparation and cleanliness are critical.

Vehicle valeting and corrosion: wash regularly, wax, clean drains and sills, treat stone chips promptly. Salt and mud accelerate corrosion; rinse underside in winter.

Record keeping: service history, mileage, parts used and torque values recorded. Warranty and resale depend on documented maintenance.

Engine capacity calculation: capacity = (π/4) × bore² × stroke × number of cylinders. Example: 4 cylinders, 75 mm bore, 80 mm stroke = 0.7854 × 5625 × 80 × 4 = 1,413,717 mm³ ≈ 1,414 cm³.

Compression ratio from measurements: CR = (Vs + Vc) / Vc. If Vs = 400 cm³ and Vc = 50 cm³, CR = 450 / 50 = 9:1.

Torque and power: power (kW) = torque (N·m) × angular velocity (rad/s) / 1000; or P (kW) = 2π × N (rpm) × T / 60,000. Example: 150 N·m at 3,000 rpm = 47.1 kW.

Gear ratio and speed: road speed (km/h) = (rpm × 60 × rolling circumference in m) / (overall ratio × 1000). Example: 3,000 rpm, 2.0 m circumference, ratio 4.0 gives 90 km/h.

Pulley and gear speeds: driven rpm = driving rpm × (driving diameter or teeth / driven diameter or teeth). A 100 mm pulley driving a 200 mm pulley at 1,000 rpm gives 500 rpm.

Tolerance and fit: clearance fit (hole larger than shaft), interference fit (shaft larger than hole), transition fit (either). Calculate allowance = minimum hole size − maximum shaft size.

Drawing projection: third-angle projection shows the top view above the front view; first-angle shows it below. Section views use hatching; cutting plane line shows where the section is taken.

Reading a drawing: identify views, scale, dimensions, tolerances, surface finish, material and notes. Check for hidden lines and centre lines before measuring.

Low oil pressure causes: low oil level, wrong viscosity, worn oil pump, blocked pickup strainer, stuck relief valve, worn main or big-end bearings, faulty sender or gauge.

High oil pressure causes: stuck relief valve, blocked filter bypass, wrong oil grade, blocked oil gallery. High pressure can damage seals and filters.

Oil consumption causes: worn rings or bores, worn valve guides and seals, leaking gaskets or seals, blocked crankcase breather (crankcase pressure pushes oil past seals).

Overheating causes: low coolant, faulty thermostat, blocked radiator, failed water pump, air lock, faulty cooling fan or sensor, slipped fan belt, blown head gasket, retarded ignition timing.

Coolant loss without visible leak: internal leak via head gasket or cracked head (white smoke, bubbles in radiator), heater matrix leak (wet carpet, sweet smell), pressure cap fault.

Thermostat test: suspend in water, heat and check opening temperature with a thermometer; should open at the marked rating (e.g. 82 °C) and close when cooled.

Water pump check: play in the shaft, noisy bearing, leaking seal (weep hole), loose or slipping belt. A loose belt causes squeal and reduced coolant flow.

Cooling system pressure test: pump to the cap rating (e.g. 1.0-1.5 bar) and watch for pressure loss or external leaks. A dropping gauge without visible leak suggests internal leakage.

Rich mixture symptoms: black exhaust smoke, sooty plugs, high CO, poor economy, rough idle. Causes: high fuel pressure, leaking injector, faulty coolant or air temperature sensor, blocked air filter.

Lean mixture symptoms: hesitation, misfire, high NOx, white or pale plugs, overheating. Causes: low fuel pressure, vacuum leak, dirty MAF sensor, clogged injector.

Misfire diagnosis: identify cylinder by disconnecting injectors or coils one at a time (where safe) or by code; check spark, compression and injector operation.

Diesel smoke colours: black = over-fuelling or restricted air; blue = oil burning; white = unburnt fuel or coolant (head gasket, injector timing, cold engine).

Common-rail diesel: high-pressure pump supplies rail; injectors are electronically controlled. Low rail pressure causes no-start; check fuel filter, low-pressure pump and rail pressure sensor.

Petrol injection: check fuel pressure, injector resistance and spray pattern, throttle position sensor, lambda sensor switching, and ignition timing.

Emission control: EGR reduces NOx by lowering combustion temperature; PCV recirculates crankcase gases; EVAP captures fuel vapour. Faults cause rough running and high emissions.

Diagnostic scan tool: read fault codes and live data (fuel trims, lambda, coolant temperature, MAF). Fuel trim positive means the ECU is adding fuel (lean); negative means removing fuel (rich).

Battery testing: open-circuit voltage after rest (12.6 V = 100 %), load test (half cold cranking amps for 15 s, voltage should stay above approx 9.6 V at 20 °C), conductance test.

Battery charging: slow charge at approx 10 % of capacity (e.g. 5 A for a 50 Ah battery) to avoid overheating. Ventilate, observe polarity, never charge a frozen battery.

Battery maintenance: keep terminals clean and tight, apply petroleum jelly, check hold-down, check electrolyte level on serviceable types (distilled water to the mark).

Alternator charging fault: warning lamp on, low voltage, dim lights. Check belt, wiring, brushes, regulator and diodes. A failed diode causes AC ripple and battery discharge.

Starter motor fault: no crank (check battery, solenoid, ignition switch, earth), slow crank (battery, cables, starter), continuous crank (stuck solenoid or ignition switch).

Ignition system: coil, distributor or coil-on-plug, spark plugs. Check spark quality, plug gap and condition (fouling, wear, colour). Electronic ignition has no points to adjust.

Lighting circuits: check bulb, fuse, relay, switch and earth. A dim lamp often indicates a poor earth connection rather than a faulty bulb.

Electrical calculations: current = power / voltage; choose cable and fuse rating above expected current with a margin. Example: 2 × 55 W headlamps at 12 V draw 9.2 A; use a 15 A fuse.

Camber: inward or outward tilt of the wheel top. Negative camber improves cornering grip but increases inner edge wear. Excessive positive camber causes outer edge wear.

Caster: forward or rearward tilt of the steering axis. Positive caster gives straight-line stability and self-centring; too much increases steering effort.

Toe: difference between front and rear of the tyres. Toe-in reduces straight-line instability; toe-out improves turn-in but increases wear. Set toe last after camber and caster.

Steering axis inclination (SAI) and included angle: SAI is the tilt of the steering axis in the front view; included angle = SAI + camber. Used to diagnose bent suspension components.

Thrust angle: the direction the rear axle points relative to the vehicle centreline. Incorrect thrust angle causes the steering wheel to be off-centre and dog-tracking.

Turning circle and Ackermann: measure the turning circle diameter; inner wheel steers more than outer. Check for tyre scrub and steering arm damage.

Ride height affects alignment: check and set tyre pressures and ride height before measuring. Sagging springs change camber and caster.

Power steering: hydraulic (pump, rack, fluid) or electric (motor, sensor). Check fluid level, belt, leaks and sensor operation. Electric steering faults often set warning lamps.

Hydraulic principle: pressure transmitted equally in all directions. Master cylinder creates pressure; caliper or wheel cylinder converts it to force. Force = pressure × piston area.

Brake servo (vacuum booster): uses engine vacuum to assist pedal effort. A hard pedal suggests a faulty servo, vacuum leak or faulty check valve.

Proportioning valve: reduces rear brake pressure to prevent rear wheel lock under heavy braking. Load-sensing valves adjust by vehicle load.

Disc brake components: disc (vented or solid), caliper (floating or fixed), pads, anti-rattle clips, dust seals. Floating caliper slides on pins and must move freely.

Drum brake components: drum, shoes, wheel cylinder, springs, adjuster, backplate. Self-servo effect increases braking force but can cause grab or lock.

Brake fluid: glycol-based DOT 3/4 hygroscopic; absorbs moisture, lowering boiling point. Silicone DOT 5 not hygroscopic but not for ABS systems unless specified.

Brake bleeding: remove air from the hydraulic system. Sequence typically furthest from the master cylinder first; keep the reservoir topped up; never let it run dry.

Parking brake: mechanical cable or electronic actuator. Must hold the vehicle on a gradient; check cable adjustment and shoe or caliper operation.