Cert III Agricultural Mech cheat sheet

Isolation before repair: shut down engine, remove key, disconnect battery earth (negative) lead first and reconnect it last, then apply lockout tag; stored energy in hydraulic accumulators, springs and raised implements must be released before work starts.

Personal protective equipment for ag mechanical work: hearing protection above 85 dB(A), safety glasses under vehicles and when grinding, steel-cap boots, gloves matched to task, and respirators for dust, paint and fuel vapour.

Jacking rule: trolley jack lifts, axle stands support; never work under a load held only by a jack or hydraulic ram, and chock the wheels remaining on the ground.

Torque formula: torque (N·m) = force (N) × lever length (m). A wrench 0.4 m long pulled with 150 N applies 60 N·m; a torque wrench reading is valid only when pulled smoothly at right angles to the handle.

Measurement tools: vernier caliper resolution typically 0.02 mm, micrometer 0.01 mm, dial indicator 0.01 mm; read the main scale first, then add the thimble or vernier coincidence value.

Four-stroke cycle order: intake, compression, power, exhaust - two crankshaft revolutions per cycle; a two-stroke fires once per revolution and uses crankcase scavenging.

Battery and charging basics: 12 V lead-acid nominal cell is 2.1 V; specific gravity near 1.265 indicates a charged cell and near 1.120 a discharged one; hydrometer readings must be temperature-corrected.

Fastener and thread rules: metric grade 8.8 bolt has tensile strength 800 MPa and yield 0.8 of that; torque values assume clean, lightly lubricated threads unless the manual states dry, and torque-to-yield bolts are replaced, not reused.

Hydraulic power: pressure (kPa) = force (N) ÷ area (m²); flow (L/min) × pressure (kPa) ÷ 60000 gives approximate power in kW, so doubling flow at the same pressure doubles available power.

Cylinder force and speed: force = pressure × piston area, speed = pump flow ÷ piston area; the rod-end area is smaller, so retract force is lower and retract speed higher than extend.

Hydraulic fault logic: slow or weak operation points to flow restriction (clogged filter, worn pump, leaking relief); excessive heat points to relief valve bypass, low oil level or blocked cooler.

Electrical basics: Ohm's law V = I × R; power P = V × I. A 24 W lamp on 12 V draws 2 A and has 6 Ω resistance; voltage drop across a circuit must be measured under load.

Charging and starting checks: a healthy 12 V battery rests near 12.6 V, cranking should not fall below about 9.6 V, and an alternator should charge at roughly 13.8–14.5 V.

Bearing and lubrication rules: over-greasing can rupture seals; grease until fresh grease appears at the relief point; bearing life falls sharply with misalignment, contamination and over-tightened belts.

Preventive maintenance schedule logic: service intervals are set by the shorter of hours or calendar time; air, fuel and oil filters are replaced together with the fluid where contamination crosses systems.

Seasonal storage: fuel stabiliser or drained tanks, batteries on maintenance charge, tyres inflated and shielded from sun, and all exposed cylinder rods coated to prevent corrosion pitting and seal damage.