Red Seal Motorcycle Technician flashcards

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

Stoichiometric air-fuel ratio

The mass ratio of air to gasoline at which complete combustion occurs, about 14.7:1 for gasoline; mixtures richer or leaner than this change power, economy, and emissions.

Compression ratio

The ratio of cylinder volume above the piston at bottom dead center to the volume at top dead center; a higher ratio raises pressure and power but requires higher octane fuel.

Valve overlap

The crank-angle period near top dead center when both intake and exhaust valves are open; it improves scavenging at speed but reduces low-speed vacuum and idle quality.

Torque-to-yield fastener

A head or main bolt tightened to a low torque plus a specified rotation angle so it stretches permanently; it must be replaced rather than reused at every teardown.

Voltage drop test

A loaded-circuit measurement of voltage lost across cables, switches, and grounds; a drop above about 0.5 V total identifies high resistance in the circuit path.

Battery state of charge

Open-circuit voltage of a rested 12 V lead-acid battery indicates charge: about 12.6 V is full, 12.4 V is 75 percent, and 12.2 V is 50 percent.

Regulator rectifier function

The unit converts stator alternating current to direct current and limits charging voltage, typically holding about 13.5 to 14.5 V to protect the battery.

Stator ground test

A resistance check from each stator phase leg to the engine case; any continuity to ground indicates an internal short and the stator must be replaced.

Chain slack measurement

Total up-and-down movement at the chain mid-span with the bike on its wheels; the manual specification is typically 20 to 35 mm and must be set before riding.

Sprocket ratio

Rear sprocket tooth count divided by front sprocket tooth count; increasing the ratio raises acceleration and lowers top speed while increasing chain speed.

Wet clutch drag

A clutch that fails to release fully, causing creeping, difficult neutral selection, and heat; causes include warped steel plates, swollen friction plates, and incorrect oil.

Suspension sag

The difference between fully extended and rider-loaded suspension length; setting sag first matches spring preload to load before damping adjustments are evaluated.

Fork oil level

The air gap measured from the tube top with the fork compressed and spring removed; it sets the air-spring effect and must be equal on both legs.

Steering head brinelling

Small indentations in the bearing races that create a detent at straight ahead; felt as notchy steering with the front wheel raised, it requires bearing replacement.

Trail

The horizontal distance between the steering axis intersection with the ground and the tire contact patch; more trail increases stability and steering effort.

Brake fluid hygroscopicity

The tendency of DOT 3 and DOT 4 fluid to absorb moisture from air; absorbed water lowers the boiling point and causes fade under hard use.

Brake pad fade

Loss of braking caused by overheated friction material, felt as a firm lever with weak stopping power; it differs from fluid boil, which gives a spongy lever.

Rotor minimum thickness

The stamped wear limit on a brake rotor; a rotor measured thinner than this value cannot absorb heat safely and must be replaced rather than resurfaced.

Master cylinder free play

The small gap that lets the piston fully return and open the compensation port; without it, fluid cannot vent and the brakes drag and overheat.

Tire aspect ratio

The sidewall height expressed as a percentage of section width; in 180/55 R17 the sidewall is 55 percent of the 180 mm width.

Tire load index

A code number matching the maximum load a tire can carry at its rated pressure; it must meet or exceed the original equipment specification.

DOT date code

The four-digit code on a tire sidewall giving week and year of manufacture; it is used to judge age-related rubber degradation independent of tread depth.

Static wheel balance

Balance achieved so the wheel does not rotate to a heavy spot when supported freely; static imbalance shows as a low-speed hop rather than a high-speed shake.

Auxiliary electrical load

The current drawn by added accessories; it must stay within the charging system spare capacity, calculated as watts divided by 12 volts.

Relay use for accessories

A small control switch energizes a relay coil so the high-current accessory circuit runs through short, heavy wiring directly from the battery fuse.

Parasitic draw

Current that flows with the key off, measured in series at the battery; accessories such as clocks and alarms can drain a battery during storage.

Pre-ride inspection

A quick check of tires, controls, lights, fluid levels, chain tension, and brakes before riding; it catches safety faults that develop between services.

Helicoil thread repair

A coiled stainless insert installed in a stripped hole to restore the original thread size; it is used for moderate loads and requires the correct drill and tap.

Road test after repair

A controlled test ride required after brake, wheel, or suspension work; begin at low speed and verify steering, brakes, and throttle return before higher speeds.

Carbon monoxide exposure

Colorless exhaust gas that binds hemoglobin far more readily than oxygen; engines must never run in an enclosed bay without exhaust capture ventilation.

Hazardous waste segregation

Separate labeled containers for used oil, coolant, brake fluid, solvents, and batteries; mixing streams makes recycling impossible and breaches regulations.

Motorcycle lift stability

A machine is stable only when strapped to a rated lift or chocked with the stand unloaded; never work beneath a bike held by a center stand alone.