Maharashtra HSC Scooter & Motorcycle Servicing (Bifocal) flashcards

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

Vernier caliper least count

Least count = 1 main scale division minus 1 vernier scale division. A vernier of 50 divisions spanning 49 mm on a 1 mm main scale reads to 0.02 mm.

Micrometer least count

Least count = screw pitch divided by thimble divisions. A 0.5 mm pitch screw with a 50-division thimble has a least count of 0.01 mm.

Feeler gauge

A set of hardened steel blades of marked thickness, used to check valve clearance, spark plug gap and piston ring side clearance by sliding the blade into the gap.

Torque wrench care

A torque wrench is a measuring instrument: return it to zero after use, never use it to loosen fasteners, and recalibrate it after a drop or an over-range pull.

Compression ratio

The ratio of cylinder total volume with the piston at bottom dead centre to the clearance volume at top dead centre; typical two-wheeler petrol engines run about 9:1 to 11:1.

Four-stroke cycle

Intake, compression, power and exhaust strokes completed in two crankshaft revolutions, or 720 degrees, giving one power stroke per cylinder every 720 degrees.

Wet sump lubrication

Oil is stored in the sump, drawn through a strainer by a trochoid pump, filtered, then pressure-fed to crankshaft, camshaft and head before draining back.

Ring end gap

The clearance between the two ends of a piston ring when squared inside the cylinder bore; too small causes ring butting and scoring, too large causes blow-by.

Stoichiometric air-fuel ratio

The mass ratio of air to petrol that burns completely with no excess oxygen or fuel; for petrol it is 14.7 to 1, and closed-loop injection targets this value.

Main jet

The carburettor jet that meters fuel from about three-quarter to full throttle; a larger main jet richens the top-end mixture and a smaller one leans it.

Catalytic converter

A honeycomb coated with platinum, palladium and rhodium that oxidises carbon monoxide and hydrocarbons and reduces nitrogen oxides in the exhaust gas stream.

Injector pulse width

The time in milliseconds for which the ECU holds the injector open; it sets fuel quantity and is calculated from airflow, rpm, throttle position and oxygen sensor feedback.

Battery specific gravity

The density of battery electrolyte compared with water; about 1.260 to 1.280 when fully charged and 1.120 or lower when discharged, measured with a hydrometer.

Regulator rectifier

Converts alternator alternating current into direct current and limits charging voltage to roughly 14.2 to 14.8 volts so the battery is not overcharged.

Spark plug heat range

A measure of how quickly the plug sheds heat; a hot plug suits low-speed engines, a cold plug suits high-speed engines, and the wrong range causes fouling or pre-ignition.

CDI ignition

Capacitor discharge ignition charges a capacitor from a source coil and discharges it through the ignition coil when a pickup coil triggers the thyristor.

Clutch lever free play

The gap before the clutch begins to disengage, typically 10 to 20 mm at the lever end; too little causes slip, too much causes drag and difficult gear selection.

Gear ratio

Driven gear teeth divided by driving gear teeth; multiplying primary, gearbox and final drive ratios gives the overall ratio from crankshaft to rear wheel.

Chain size 428

A roller chain with 4/8 inch, or 12.7 mm, pitch; the last two digits indicate roller width, and the number is stamped on the side plates for replacement matching.

Variator rollers

Rounded weights in a scooter continuously variable transmission that move outward with engine speed to change belt ratio; flat spots reduce acceleration and top speed.

Trail

The horizontal distance between where the steering axis meets the ground and the front tyre contact patch; more trail gives stability, less trail gives quicker steering.

Tyre size 90/90-17

90 mm nominal section width, aspect ratio 90 percent giving 81 mm sidewall height, and a 17-inch rim; load and speed symbols follow the size on the sidewall.

Static sag

The amount the suspension compresses under the vehicle's own weight; set by spring preload to keep ride height and geometry correct with or without a pillion.

Wheel runout

Side-to-side axial and up-down radial wobble of a rotating wheel measured with a dial gauge; about 2 mm is a common service limit before truing or replacement.

DOT 4 brake fluid

A glycol-based hydraulic fluid that is hygroscopic; absorbed moisture lowers its boiling point and causes brake fade and a spongy lever, so it is replaced periodically.

Weight transfer under braking

Load moves forward when braking, so the front tyre carries most of the grip; the front brake supplies roughly 70 to 80 percent of stopping force on a two-wheeler.

Combined braking system

A linkage that applies some front brake when the rear pedal is pressed, distributing braking force and shortening stopping distance for less skilled riders.

Brake pedal free play

The travel before the brake shoes contact the drum, usually 10 to 20 mm; excess play means the brake is not fully released or the lining is worn.

Compression test

Cranking a warm engine at wide-open throttle and reading peak cylinder pressure; a healthy two-wheeler gives about 9 to 12 bar and a low reading indicates leakage.

Job card

The workshop document recording customer complaint, odometer reading, diagnosis, work done, parts replaced, labour charges and the next service due date.

Vacuum gauge diagnosis

A gauge connected to the intake reads engine breathing; a steady low reading suggests an intake leak, a fluctuating needle suggests sticking valves or weak springs.

Periodic maintenance schedule

The manufacturer's table of service tasks and intervals; the first service falls at about 500 to 750 km, with later services typically every 3,000 to 6,000 km.