SOLAS Heavy Vehicle Mechanic flashcards

32 cards. Read the term and the definition here. The deck at the top of this page is optional.

Four-stroke cycle order

Intake, compression, power, exhaust. The crankshaft turns twice and the camshaft once per complete cycle in a four-stroke engine.

Engine displacement formula

Displacement equals bore area times stroke times cylinder count, where bore area is pi times half the bore squared.

Diesel compression ratio range

Typically 16:1 to 22:1. High compression raises intake air temperature enough for injected fuel to self-ignite without a spark plug.

Torque wrench extension correction

When an adapter extends effective length, set the wrench to target torque multiplied by wrench length divided by total effective length.

Common rail injection pressure

Modern heavy diesel common rail systems can exceed 2000 bar. High-pressure lines must never be cracked open while the engine runs.

Hydraulic pressure formula

Pressure equals force divided by piston area. Doubling the piston area halves the pressure required to produce the same output force.

Pump flow calculation

Flow in litres per minute equals pump displacement in cubic centimetres per revolution times rpm, divided by one thousand.

Relief valve function

It limits maximum system pressure by bypassing flow. A valve stuck open causes slow actuator movement and rapid fluid heating.

ISO VG viscosity grade

The grade number is the kinematic viscosity in square millimetres per second measured at 40 degrees Celsius; VG 46 is about 46.

Brake fluid hygroscopy

DOT 4 fluid absorbs moisture from air. Absorbed water lowers boiling point and can cause vapour lock during sustained heavy braking.

Ohm's law and power

Voltage equals current times resistance. Power equals voltage times current, or current squared times resistance, in a direct current circuit.

Series versus parallel circuits

In series, resistance adds and current is common. In parallel, voltage is common and total resistance is the reciprocal sum.

24 V battery configuration

Two 12 V batteries connected in series give 24 V. If one fails open, the entire string stops supplying current.

Voltage drop test purpose

Measured under load, excessive drop across a cable or connection shows resistance. Above roughly 0.5 V on heavy cables is suspect.

CAN bus termination resistance

Each end of the bus has a 120 ohm terminator. Measuring near 60 ohms across the data lines indicates both terminators are present.

Alternator regulated output

A 24 V charging system is regulated to roughly 27.5 to 28.5 V. Readings outside this band suggest regulator or sense-line faults.

Governor cut-out pressure

Air compressor unloading typically occurs near 800 to 850 kPa, with cut-in about 100 to 150 kPa lower to restart compression.

Air brake leak test limit

With engine off and brakes released, pressure loss above about 20 kPa per minute indicates a leak needing repair before service.

Slack adjuster pushrod stroke

Stroke beyond the adjustment limit requires resetting the slack adjuster or replacing the chamber. Automatic types set on a full application.

Spring brake caging bolt

The caging bolt mechanically compresses the parking spring for release during repair. It must be removed before the vehicle returns to service.

Air dryer desiccant failure

Saturated desiccant passes moisture downstream. Oil carry-over from a worn compressor contaminates the desiccant and accelerates failure.

Gladhand colour coding

Trailer couplers are colour coded: blue for the service line and red for the supply line, matching the coiled hoses.

Wheel nut lubrication effect

Lubricated threads convert more applied torque into clamp load. Always follow the manufacturer's dry or lubricated specification.

Tyre load index requirement

The tyre load index and speed symbol must meet or exceed the axle rating and placard values. Never fit a lower load index.

Wheel alignment ride height

Air suspension ride height must be set before alignment. Incorrect height alters camber and caster readings and skews results.

Hub bearing preload

Bearings are set to a specified end-float or preload. Over-tightening causes overheating, while excess play causes uneven tyre wear.

Welding near vehicle electronics

Disconnect the battery negative and unplug electronic control units before welding to protect circuits from stray welding current.

Lock-out tag-out sequence

Isolate every energy source, release stored pressure or spring force, verify zero energy with a test, then attach the tag.

Jack stand placement

Stands rated above the axle load are placed under structural chassis points. A hydraulic jack lifts but never supports a vehicle.

Hearing protection threshold

Hearing protection is required where noise exposure exceeds 85 decibels averaged over an eight-hour working day.

Aftertreatment component roles

The diesel oxidation catalyst treats hydrocarbons and carbon monoxide, the filter traps soot, and selective catalytic reduction cuts nitrogen oxides.

DPF regeneration temperature

Soot burns off above roughly 550 degrees Celsius exhaust temperature. Short low-load duty cycles prevent passive regeneration and load the filter.