Cert III Automotive Mechanic flashcards

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

Hierarchy of control order

Ranked from most to least effective: elimination, substitution, engineering controls, administrative controls, then personal protective equipment. PPE is the last line of defence because it protects only the wearer and relies on correct use.

Safety data sheet sections

A 16-section document covering identification, hazards, composition, first aid, firefighting, spill response, handling and storage, exposure controls, physical properties, stability, toxicology, ecology, disposal, transport, and regulatory information.

Class B fire

A fire involving flammable liquids such as petrol, solvent, or oil. Extinguish with foam, dry chemical, or carbon dioxide. Water is unsuitable because it can spread the burning liquid and endanger the operator.

Torque wrench calibration tolerance

Most workshop torque wrenches are accurate to about plus or minus four percent of the set value. Recalibrate annually and after any drop, over-range use, or long storage at full setting.

Micrometer reading method

Read the barrel scale for whole and half millimetres, then add the thimble value. Each thimble division on a metric micrometer equals 0.01 mm, so a thimble reading of 23 adds 0.23 mm.

Tap drill size rule

For metric coarse threads, subtract the pitch from the nominal diameter. An M8 x 1.25 thread therefore uses a 6.75 mm drill, giving roughly 75 percent thread engagement in most materials.

Cylinder leakage test

Air is fed into a cylinder at top dead centre on compression and the percentage lost is read. Above about 20 percent indicates a sealing fault; escaping air location identifies rings, intake valve, or exhaust valve.

Compression ratio formula

Compression ratio equals swept volume plus clearance volume, divided by clearance volume. A ratio of 10:1 means the charge is squeezed into one tenth of its original volume at top dead centre.

Interference engine risk

An engine where valve and piston paths overlap. If the timing belt or chain breaks or jumps, pistons strike open valves, causing bent valves, damaged pistons, and expensive head repairs.

Ohm's law

Voltage equals current multiplied by resistance, written V equals I times R. Rearranged, current is voltage divided by resistance and resistance is voltage divided by current. Power in watts is volts times amps.

Battery state of charge

A rested lead-acid battery reads about 12.6 volts at full charge, 12.2 volts at half charge, and 12.0 volts or less when discharged. Charging systems normally hold 13.8 to 14.7 volts.

Voltage drop testing

Measure voltage lost across a circuit while current flows. A drop above 0.5 volts on a high-current circuit such as a starter cable indicates excessive resistance from corrosion or a poor connection.

Hydraulic pressure relationship

Pressure equals force divided by piston area. A larger master cylinder bore moves more fluid but produces lower line pressure for the same pedal force, which can make the pedal feel firmer yet less powerful.

Spongy versus sinking pedal

A spongy pedal that feels springy indicates air in the hydraulic circuit and needs bleeding. A pedal that sinks slowly under steady pressure indicates internal master cylinder bypass or an external leak.

Brake rotor minimum thickness

The discard thickness is stamped on the rotor hub or edge. Machining or continued wear must not take the rotor below that value, because a thin rotor overheats, warps, and may crack under load.

Camber angle definition

The vertical tilt of the wheel viewed from the front. Positive camber leans the top outward, negative leans it inward. Excessive negative camber wears the inner tyre edge and reduces straight-line grip.

Caster angle effect

The tilt of the steering axis viewed from the side. More positive caster improves straight-line stability and self-centring but increases steering effort. Too little caster causes wander and vague steering feel.

Toe wear pattern

Incorrect toe scrubs tyres sideways, producing feathered wear with sharp edges on one side of each tread block. It is the most common alignment fault causing rapid tyre replacement.

Manual gear ratio

Driven gear tooth count divided by drive gear tooth count. Overall ratio multiplies gearbox ratio by final drive ratio, so a 3.5 first gear with a 3.9 final drive gives 13.65 to one.

Clutch pedal free play

The small gap before the release bearing contacts the pressure plate, typically 20 to 25 millimetres at the pedal. Too little free play keeps the bearing loaded and can cause slipping and rapid wear.

Automatic transmission fluid check

Most units are checked with the engine running, transmission in park or neutral, and fluid at operating temperature. Overfilling aerates the fluid, causing erratic shifts and possible overheating.

Coolant mixture ratio

A 50/50 mix of ethylene glycol concentrate and water protects to about minus 37 degrees Celsius and raises the boiling point above 125 degrees Celsius when pressurised. Never use plain water alone.

Oil viscosity grade meaning

In a grade such as 5W-30, the first number rates cold pumping behaviour and the second rates viscosity at 100 degrees Celsius. Always use the grade and specification the manufacturer requires.

Fuel trim interpretation

Short-term and long-term fuel trim show how much the engine computer adjusts fuelling. Trims beyond about plus or minus 10 percent indicate a vacuum leak, faulty sensor, or fuel delivery problem.

Three-way catalytic converter

This converter oxidises hydrocarbons and carbon monoxide while reducing nitrogen oxides. It works efficiently only when the engine runs in closed loop near the stoichiometric air-fuel ratio.

Positive crankcase ventilation

A valve routes crankcase blow-by gases back into the intake for burning. A blocked valve pressurises the crankcase, causing oil leaks and rough idle; a stuck valve can lean the mixture.

Oxygen sensor switching

A healthy upstream oxygen sensor switches rapidly between roughly 0.1 and 0.9 volts. A slow or lazy sensor causes poor fuel economy, high emissions, and possible catalyst damage.

Roadworthy inspection scope

A safety inspection checks tyre tread and condition, brake performance, lights, steering play, suspension, seat belts, windscreen, body structure, and rust, confirming the vehicle is safe to operate.

Repair order requirements

A repair order records customer details, vehicle identification number, odometer, the complaint in the customer's own words, authorised work, and the signature or documented approval for that work.

Vehicle identification number

A 17-character code identifying manufacturer, model attributes, and a check digit. It confirms exact build details so the correct parts are ordered and the repair history is linked to the right vehicle.

Consumer guarantee for services

Australian consumer law requires services be delivered with due care and skill and be fit for purpose. These guarantees apply automatically and cannot be excluded by a workshop contract.

Written authorisation before extra work

A workshop must obtain and record customer approval before exceeding the agreed quote. The record should note the time, the person approving, and the additional scope of work authorised.