BTEB Motorcycle Servicing cheat sheet

Personal protective equipment for motorcycle work: eye protection, nitrile gloves for fuel and solvent, steel-toe boots, and hearing protection when using impact tools or air compressors.

Carbon monoxide is odourless and binds haemoglobin about 200-250 times more readily than oxygen; never run an engine in an enclosed bay without forced ventilation.

Petrol flash point is about -43 degrees Celsius; its vapour is heavier than air and can travel along the floor to an ignition source several metres away.

Class B fire extinguishers (foam, dry powder, CO2) suit flammable liquids; water must never be applied to a petrol fire because it spreads the burning fuel.

Battery electrolyte contains sulphuric acid; acid spills are neutralised with sodium bicarbonate solution, and eye contact requires immediate flushing with water for at least 15 minutes.

Safe manual handling: keep the load close to the body, bend the knees, keep the spine neutral, and use two persons or a lift table for engines and frames above roughly 25 kg.

Asbestos in old clutch and brake linings is a respirable hazard; use a wet method or enclosed vacuum extraction, never dry compressed air, when cleaning friction parts.

Waste segregation: used oil, filters, solvents, and lead-acid batteries are separate hazardous streams; used oil must never be mixed with solvent or brake fluid.

A spanner must fit the fastener flats fully; an open-end spanner that is one size too large rounds hex heads and slips under torque.

Torque = force x perpendicular distance (T = F x d); a 200 N force on a 0.25 m wrench applies 50 N.m.

Six-point sockets contact the flats and resist rounding better than 12-point sockets, which are chosen for access angle rather than high torque.

A torque wrench is a measuring instrument: store it at its lowest setting, never use it to loosen fasteners, and recalibrate after a drop.

Screwdriver tip size must match the slot or cross recess; a worn or undersized tip cams out and damages both the tip and the fastener head.

Feeler gauges measure clearance by drag; the correct gap is the largest blade that enters with slight resistance and the next size up that will not enter.

A file cuts on the forward stroke only; pressure is released on the return stroke to preserve the teeth and produce a flat surface.

Micrometer and vernier callipers are precision instruments; they are checked against a zero reading before use and kept clear of abrasive dust and impact.

Vernier calliper reading = main scale value + (coinciding vernier division x least count); a 0.02 mm calliper resolves 1/50 of a millimetre.

Micrometer least count = pitch of screw (0.5 mm) divided by thimble divisions (50) = 0.01 mm; the sleeve also carries a 0.5 mm datum line.

Cylinder bore taper and out-of-round are found by measuring at three heights and two directions (parallel and perpendicular to the crankshaft axis).

Bore clearance = measured cylinder bore minus measured piston skirt diameter at the specified height and 90 degrees to the gudgeon pin.

A dial test indicator reads runout; shaft or disc runout limits are usually given as a total indicator reading in the service data.

Plastigauge is a crushable plastic strip; its flattened width, compared with the printed scale, gives the bearing oil clearance without a bore gauge.

Cylinder honing cross-hatch angle of roughly 45 degrees retains oil film and aids ring bedding; too shallow an angle causes oil consumption.

Workshop practice: clean parts before measurement, allow them to reach room temperature (about 20 degrees Celsius), and record readings against the service limit, not the nominal value.

Four-stroke cycle: intake, compression, power, exhaust, each occupying two crankshaft revolutions (720 degrees) with one power stroke per cylinder.

Two-stroke cycle completes intake, compression, power, and exhaust in one crankshaft revolution, using crankcase compression and transfer ports instead of valves.

Compression ratio = (swept volume + clearance volume) / clearance volume; a 150 cc cylinder with 15 cc clearance gives 11:1.

Swept volume of one cylinder = (pi/4) x bore squared x stroke; total displacement is that value multiplied by the number of cylinders.

Valve overlap is the period when both intake and exhaust valves are open around top dead centre; it aids scavenging and is measured in crank degrees.

Overhead cam layouts reduce reciprocating valve-train mass compared with pushrod layouts, allowing higher safe engine speeds.

Firing order and crankpin phasing determine vibration characteristics; a 360-degree parallel twin fires both pistons together, a 180-degree crank gives even firing.

Knocking (detonation) is spontaneous ignition of end gas after the spark; causes include low octane fuel, excessive compression, lean mixture, and hot spots.

Tune-up sequence: valve clearance, spark plug condition and gap, ignition timing, air filter, carburettor or injection synchronisation, then idle speed and mixture.

Valve clearance is set with the engine cold on most air-cooled engines and at the specified stroke; too little clearance causes hard starting and burnt valves.

Cylinder compression test: throttle wide open, engine warm, all plugs removed; a reading below the service limit or a large spread between cylinders indicates leakage.

A leak-down test localises compression loss: air escaping at the exhaust means exhaust valve, at the intake means intake valve, at the oil filler means rings or piston.

Piston ring end gap is measured with the ring squared in the bore; insufficient gap causes ring butting and breakage when hot.

Head bolt torque is applied in a spiral or cross pattern in two or three stages to the specified figure, using new gaskets and clean threads.

Engine overhaul replacement rules: parts at or beyond the wear limit, out-of-round bores, scored journals, and stretched timing chains are renewed, not reused.

After overhaul, break-in requires moderate load variation, no sustained full throttle, and an early oil and filter change to remove assembly debris.

Stoichiometric air-fuel ratio for petrol is about 14.7:1 by mass; rich mixtures (below this) cool combustion, lean mixtures raise temperature and risk detonation.

Carburettor circuits: float and needle valve control level, pilot circuit handles idle and off-idle, needle and slide handle mid-range, main jet handles full throttle.

Fuel injection delivers by pulse width; a long pulse or high fuel pressure both enrich the mixture, so pressure must be checked before condemning an injector.

Ignition timing is measured in degrees before top dead centre; over-advanced timing causes knocking and hard starting, retarded timing causes overheating and poor power.

Spark plug heat range: a hot plug runs a longer insulator nose and suits low-load engines; a cold plug sheds heat faster and suits sustained high speed.

Oil viscosity grade such as 10W-40: the first number is the low-temperature pumping characteristic, the second is the kinematic viscosity at 100 degrees Celsius.

Oil pressure warning at idle with correct level usually indicates a worn pump, a stuck relief valve, or excessive bearing clearance, not simply old oil.

Liquid cooling: the thermostat opens near 80-90 degrees Celsius; a pressure cap raises boiling point by roughly 3 degrees Celsius per 0.1 bar of rating.

Primary reduction, gearbox ratio, and final drive ratio multiply together; overall ratio = engine speed / wheel speed, so lower numeric ratio means higher potential speed.

Constant-mesh gearbox: gears stay engaged and dogs or sliding forks select the pair; a jumping-out-of-gear fault points to worn dogs or a bent shift fork.

Wet multiplate clutch clearance is set by the pushrod and cable free play, typically 10-20 mm at the lever; zero free play causes slip and rapid plate wear.

Clutch slip under load with correct free play indicates worn friction plates, weak springs, or glazed steel plates; drag on engagement indicates warped plates.

Chain drive: slack is measured at the midpoint of the lower run, typically 20-30 mm; too tight loading destroys countershaft and wheel bearings.

Chain wear limit is reached when a specified number of links spans beyond the service length; a worn chain also hooks the sprocket teeth.

Belt drive tension is set by deflection under a specified force; belts must not be twisted, kinked, or contaminated with oil or solvent.

Shaft drive uses a bevel or hypoid final gear with its own oil level; hypoid gears require extreme-pressure (EP) lubricant, not engine oil.

Hydraulic brake advantage: pressure is transmitted equally (Pascal's law), so a small master-cylinder piston force creates large calliper clamping force.

Brake fluid is hygroscopic; absorbed moisture lowers boiling point and causes spongy lever feel or fade under repeated heavy braking, so fluid is replaced periodically.

A spongy brake lever with no external leak indicates air in the hydraulic circuit; bleeding removes it from the lowest point, the calliper bleed nipple.

Disc thickness and runout are measured against service limits; below minimum thickness the disc must be replaced, not machined further.

Suspension sag is the difference between fully extended and rider-loaded length; it sets ride height and must be checked before adjusting damping.

Fork oil level and viscosity control damping; unequal levels between legs cause pulling and uneven behaviour over bumps.

Steering head bearing free play is checked with the front wheel clear of the ground; excess play causes a clunk and weave, too tight causes notchy steering.

Wheel alignment and tyre pressures affect steering: under-inflation increases rolling drag and causes cupping and heavy steering.

Ohm's law: V = I x R; power P = V x I. A 12 V circuit drawing 4 A has 3 ohms resistance and dissipates 48 W.

Series circuit: current is common, voltages add. Parallel circuit: voltage is common, currents add; motorcycle loads are wired in parallel.

A 12 V lead-acid battery has six cells at about 2.1 V each; open-circuit voltage near 12.6 V indicates full charge, 12.0 V roughly half charge.

Specific gravity of electrolyte falls with discharge; a hydrometer reading near 1.265 indicates full charge and near 1.120 indicates discharged.

Charging system check: battery voltage should rise to roughly 13.5-14.5 V at mid engine speed; a lower figure points to a faulty regulator, rectifier, or stator.

Stator output is alternating current; the rectifier converts it to direct current and the regulator limits voltage to protect the battery and lamps.

Voltage drop testing locates high-resistance connections: a drop above about 0.5 V on a loaded circuit indicates a corroded or loose joint.

Electrical fault finding order: battery state of charge, fuses, connections and earths, then component tests; a poor earth mimics a failed component.

Periodic maintenance intervals are set by distance or time, whichever comes first; dusty or short-trip use shortens the interval for filters and oil.

Daily or pre-ride checks: tyre pressure and condition, brake operation, lights and horn, oil level, fuel level, and drive chain or belt condition.

Troubleshooting logic: confirm the complaint, verify with a test, isolate the system, test components in order of likelihood and ease, then repair and re-verify.

Hard starting with a good spark and fuel supply points to compression or valve clearance; a no-spark condition points to ignition, kill switch, or side-stand switch.

Overheating causes divide into low coolant or oil, lean mixture, retarded timing, dragging brakes, and a blocked cooling fin or radiator core.

Customer service record: note the complaint in the customer's words, the diagnosis, parts fitted, labour, and the warranty terms on the job card.

A repair estimate must list parts and labour separately and be agreed before work begins; unexplained extra work is a common source of complaints.

Road test after service confirms the repair under load and checks that brakes, steering, and controls return correctly before the machine is handed over.

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