SOLAS Heavy Vehicle Mechanic cheat sheet

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

Diesel compression ignition needs compression ratio typically 16:1 to 22:1 to raise intake air above the fuel's auto-ignition temperature.

Engine displacement = bore area × stroke × number of cylinders; bore area = π × (bore/2)².

Valve clearance is measured with the engine cold unless the manufacturer specifies hot settings; feeler gauge drag should be a light sliding fit.

Torque = force × perpendicular distance; a 300 mm wrench pulled with 200 N applies 60 N·m before any extension correction.

Extending a torque wrench with an adapter changes effective length: required wrench setting = target torque × (wrench length ÷ total effective length).

Common rail diesel injection pressure can exceed 2000 bar; never crack a high-pressure line while the engine is running.

Timing belt replacement intervals are specified in kilometres or years, whichever comes first; tensioner and idler pulleys are replaced with the belt.

Hydraulic pressure = force ÷ piston area; doubling piston area halves the pressure needed for the same force.

Flow rate = swept volume × rotational speed; pump displacement in cm³/rev multiplied by rpm and divided by 1000 gives litres per minute.

Relief valve limits maximum system pressure; a relief valve stuck open causes slow or no actuator movement and fluid heating.

Air in hydraulic oil causes spongy operation and aeration foam; bleed at the highest point and check suction-line tightness.

ISO VG grade denotes kinematic viscosity at 40 °C in mm²/s; VG 46 oil is about 46 mm²/s at 40 °C.

Hydraulic filter restriction indicators show when bypass occurs; operating in bypass sends contaminated oil to components.

Accumulators store pressurised fluid; depressurise per manufacturer procedure before any work on the circuit.

DOT 4 brake fluid is hygroscopic; absorbed moisture lowers boiling point and can cause vapour lock under sustained braking.

Ohm's law: V = I × R; power P = V × I = I²R. A 24 V circuit drawing 10 A dissipates 240 W in its load.

Series circuit: total resistance is the sum, current is common, voltages add. Parallel circuit: voltage is common, currents add, 1/Rt = 1/R1 + 1/R2.

A 24 V system has two 12 V batteries in series; a single 12 V battery failing open-circuits the whole string.

Voltage drop should be measured under load; a reading above about 0.5 V on a heavy-vehicle charging or starter cable indicates excessive resistance.

Alternator output is regulated to roughly 27.5–28.5 V on a 24 V system; sustained readings outside this band indicate regulator or sense-line faults.

Starter current draw can exceed 1000 A on large diesels; clamp meters must be rated for the inrush and DC measurement.

CAN bus needs 120 Ω termination at each end; a bus reading near 60 Ω across the data lines indicates both terminators are present.

LED and ECU loads are polarity sensitive; test lamps with low impedance can damage driver outputs, so use high-impedance meters or LED-safe probes.

Air brake system pressure builds to governor cut-out around 800–850 kPa; cut-in is typically 100–150 kPa lower.

A pressure loss exceeding about 20 kPa per minute with the engine off and brakes released indicates a leak requiring repair before service.

Pushrod stroke beyond the adjustment limit means the slack adjuster must be reset or the chamber replaced; automatic slack adjusters require a full brake application to set.

Spring brake chambers use stored spring force for parking; caging bolts are for release only and must be removed before the vehicle returns to service.

Brake drum diameter is measured with a drum gauge; exceeding the maximum rebore limit requires drum replacement.

Air dryer desiccant saturates over time; oil carry-over from a failing compressor destroys desiccant and passes moisture downstream.

ABS wheel speed sensors must have correct air gap; metal debris on the sensor face causes intermittent fault codes at low speed.

Gladhand couplers use colour coding: blue for service line, red for supply line on trailers.

Wheel nut torque is applied dry or lubricated per manufacturer specification; lubricated threads convert more torque into clamp load.

Dual wheels need equal clamp load on both; a loose inner nut causes stud fatigue and wheel loss.

Tyre load index and speed symbol must meet or exceed the axle rating; never fit a lower load index than the placard.

Tread depth legal minimum for heavy vehicle steer tyres is generally 3 mm across specified bands; check local regulation.

Run-out and imbalance cause irregular wear; radial run-out is measured with a dial gauge against the tyre sidewall.

Wheel alignment toe-in is set with the vehicle at kerb weight; incorrect toe scrubs tyres and increases fuel use.

Hub bearings are set by end-float or preload specification; over-tightening causes overheating and premature failure.

Air suspension ride height must be set before alignment; incorrect height changes camber and caster readings.

Before welding on a vehicle, disconnect battery negative and unplug ECUs to protect electronics from welding current.

Fuel and brake lines must be removed or shielded before any heat application; a pinhole leak becomes a fire risk.

Lock-out/tag-out: isolate energy sources, release stored pressure, verify zero energy, then tag before repair.

Jack stands must be rated above the axle load and placed on structural chassis points, never on the sump or fuel tank.

A vehicle supported only by a hydraulic jack is unsafe; the jack is a lifting device, not a support.

Hearing protection is required where noise exceeds 85 dB(A) averaged over an eight-hour day.

Waste oil, coolant, and batteries are regulated waste streams; store separately and dispose through licensed contractors.

Refrigerant recovery is mandatory before opening an air-conditioning circuit; venting refrigerant to atmosphere is prohibited.

Diesel exhaust aftertreatment: DOC oxidises hydrocarbons and CO, DPF traps soot, SCR uses urea to reduce NOx.

DPF regeneration requires exhaust temperature typically above 550 °C; short-duty cycles prevent passive regeneration and cause soot loading.

Diesel particulate filter differential pressure rising steadily indicates soot accumulation; a sudden high reading may indicate a cracked filter.

SCR systems monitor DEF quality and level; derate strategies reduce engine power when DEF is empty or contaminated.

EGR coolers leaking coolant into the intake produce white smoke and coolant loss without external leaks.

OBD fault codes should be recorded before clearing; freeze-frame data helps confirm the operating conditions at fault set.

Smoke colour diagnosis: black suggests over-fuelling or restricted air, blue suggests oil consumption, white suggests unburnt fuel or coolant.

Injector coding must match the ECU after replacement; incorrect coding causes rough running and increased emissions.