Cert III Motorcycle Mech cheat sheet

Personal protective equipment for motorcycle workshop tasks: eye protection when grinding or using compressed air, hearing protection above 85 dB(A), nitrile gloves for fuel and solvent contact, and steel-capped boots when handling engines and frames.

Four-stroke cycle order is intake, compression, power, exhaust; the crankshaft completes two revolutions per cycle, so camshaft speed is half crankshaft speed in a four-stroke engine.

Valve clearance is measured with the engine cold unless the manufacturer specifies otherwise, and is set at the point where the cam base circle faces the follower (TDC on compression for most single-cylinder engines).

Torque values are applied with a calibrated wrench to the thread and fastener condition specified; lubricated threads reduce friction and can increase clamp load by roughly 20-30 percent at the same torque figure.

Compression test procedure: engine at operating temperature, throttle wide open, all spark plugs removed, crank until the gauge stops rising; a reading below about 70 percent of specification or a large spread between cylinders indicates a fault.

Hazardous substances in the workshop include petrol (flash point around -43 degrees C), brake fluid (damages paint, hygroscopic), and used engine oil (skin irritant, carcinogenic risk with prolonged contact); each requires a safety data sheet kept on site.

Manual handling rule: keep the load close to the body, bend at the knees and hips, avoid twisting under load, and use a hoist or two-person lift for engines and complete frames above about 20 kg.

Isolation before work on electrical or fuel systems: disconnect the battery negative terminal first and reconnect it last, and relieve fuel pressure at the specified test point before opening any high-pressure line.

Chain slack is measured at the midpoint of the lower run with the motorcycle on its side stand or specified unladen position; typical specification is 20-35 mm, and adjustment is made at the rear axle with alignment checked against the swingarm marks or a string line.

Brake fluid is hygroscopic; DOT 4 has a minimum dry boiling point of 230 degrees C and wet boiling point of 155 degrees C, and fluid is typically replaced every 1-2 years or when moisture content exceeds about 3 percent.

Disc brake minimum thickness is stamped on the disc carrier; below that figure the disc is replaced, and runout is checked with a dial gauge, commonly limited to about 0.15-0.30 mm depending on the model.

Battery open-circuit voltage indicates state of charge: about 12.6-12.8 V is fully charged, 12.2 V is roughly 50 percent, and below 11.8 V is discharged; a resting reading is taken at least 30 minutes after charging or running.

Charging system check: with the engine running at about 2000-3000 rpm, regulated voltage typically sits between 13.5 and 14.8 V; a reading outside that range points to the regulator/rectifier or stator.

Wheel bearing check: lift the wheel, spin it, and feel for roughness or play at the rim; axial play above the manufacturer's limit or any notchiness requires bearing replacement, and bearings are pressed on the inner race only.

Suspension setup order: set static and rider sag first (typically 25-35 mm rear, 20-30 mm front), then rebound, then compression; damping clicks are counted from fully seated (clockwise) outward.

Tyre pressures are set cold; a pressure rise of more than about 10 percent after a ride indicates underinflation or overheating, and the tyre date code (four digits, week and year) identifies age for replacement decisions.