Motorcycle/Small Engine NC II cheat sheet

Personal protective equipment for servicing work: safety glasses or goggles, nitrile gloves for fuel and solvent contact, steel-toe boots, and hearing protection above 85 dB(A).

Exhaust gas carbon monoxide is colorless and odorless; never run an engine in an enclosed space without forced ventilation and a CO monitor.

Battery charging releases hydrogen gas, which is explosive between roughly 4% and 75% concentration in air; charge in a ventilated area with no open flame or spark.

Fuel flash point (gasoline) is about -43 °C, so fuel vapor ignites at ambient temperature; bond and ground containers during transfer to prevent static spark.

Waste segregation rule: used oil, used coolant, solvent sludge, and lead-acid batteries are hazardous and must never enter drains, soil, or general refuse.

Spill response order: stop the source, contain with absorbent, collect into a labeled closed container, then clean the area and record the incident.

Lifting rule: keep the load close, back straight, lift with legs; two-person lift or hoist above roughly 25 kg for a single worker.

Fire extinguisher selection: Class B (CO2 or dry chemical) for fuel and solvent fires; never water on fuel fires or on live electrical equipment.

Compressed air for cleaning must be below 30 psi (207 kPa) with a chip guard; never point air at skin or use it to clean clothing.

Micrometer reading = barrel main scale + thimble reading; least count on a metric 0.01 mm micrometer is 0.01 mm per thimble division.

Vernier caliper reading = main scale value + (coinciding vernier line × least count); a 0.02 mm caliper has 50 vernier divisions.

Cylinder bore measurement uses a bore gauge or inside micrometer read at three heights (top, middle, bottom) and two axes (parallel and perpendicular to the crankshaft).

Cylinder taper = largest bore minus smallest bore along the axis; out-of-round = maximum minus minimum diameter at the same height.

Torque wrench accuracy is specified at a percentage of full scale (commonly ±4%); store click-type wrenches at the lowest setting to protect the spring.

Feeler gauge measures valve clearance, piston ring end gap, and spark plug gap by selecting the blade that produces light drag.

Dial indicator with magnetic base measures crankshaft runout, shaft end play, and disc/rotor lateral runout; zero the indicator before reading.

Plastigauge measures bearing oil clearance: tighten to spec, disassemble, and compare the crushed strip width to the printed scale.

Torque conversion: 1 kgf·m = 9.807 N·m; 1 lbf·ft = 1.356 N·m; 1 lbf·in = 0.113 N·m.

Engine oil change interval is set by the manufacturer; check level with the bike upright and the dipstick or sight glass per manual procedure, not by guess.

Valve clearance is checked with the engine cold (or per manual) at TDC on the compression stroke; incorrect clearance causes noise, hard starting, or burned valves.

Drive chain slack is measured mid-span between sprockets with the bike on its side stand or as specified; typical free play is 20-30 mm.

Chain wear limit is reached when 20 links (or the manual's span) exceed the specified length; replace chain and sprockets as a set.

Air filter service: foam elements are washed, dried, and oiled; paper elements are tapped or blown from the inside out and replaced when damaged or saturated.

Brake fluid is hygroscopic; flush per interval (commonly every 1-2 years) and never mix DOT 3/4 with DOT 5 silicone or mineral oil systems.

Battery open-circuit voltage approximates state of charge: about 12.6-12.8 V fully charged, 12.4 V at 75%, 12.2 V at 50%, 12.0 V at 25%.

Fastener check sequence: follow the manual's torque pattern (usually crisscross or spiral from center outward) and replace torque-to-yield or damaged fasteners.

Tire check: cold inflation pressure per placard, tread depth minimum 1.6 mm (1/16 in) in the grooves, and sidewall for cracks or age codes.

Diagnostic sequence: verify the complaint, gather symptoms, form a hypothesis, test the simplest and most likely cause first, then confirm the repair restores normal operation.

No-start with no spark: check kill switch, side-stand switch, clutch switch, then battery, ignition coil primary/secondary resistance, and pickup/pulser coil gap.

Voltage drop test: measure from source to load under load; more than about 0.5 V drop on a starter circuit indicates high resistance in cable or connection.

Ohm's law: V = I × R; power P = V × I = I²R. A 12 V circuit drawing 2 A dissipates 24 W and has 6 Ω resistance.

Charging system check: battery voltage should rise to roughly 13.5-14.5 V at mid-rpm with lights on; low or absent rise points to stator, regulator/rectifier, or wiring.

Compression test: throttle wide open, engine warm, spin until gauge peaks; low reading that improves with oil added suggests worn rings, not valves.

Leak-down test: apply regulated air at TDC compression; air from the exhaust = exhaust valve, from the intake = intake valve, from the dipstick = rings.

Spark plug reading: black soot = rich mixture or weak ignition; white/blistered = lean or overheating; tan/gray = normal combustion.

Fuel system fault isolation: confirm fuel reaches the float bowl or injector, then check float level, jet/passage cleanliness, and air leaks at the intake boot.

Cylinder wear limits: compare measured bore to the manual's standard and service limit; rebore or replace when taper, out-of-round, or wear exceeds limit.

Piston-to-cylinder clearance is measured at the piston skirt, 90° to the pin, at a specified height; too tight seizes, too loose causes slap and blow-by.

Ring end gap is checked by squaring the ring in the bore with a piston; too small a gap causes ring breakage from thermal expansion.

Ring installation: compression rings with the marked side up, gaps staggered about 120° apart, and the oil ring expander ends butted, not overlapped.

Valve seat contact should be centered on the valve face, typically 1-1.5 mm wide; grind or cut to spec and lap, then check with Prussian blue.

Valve stem-to-guide clearance is measured with a dial gauge or by comparing stem OD to guide ID; excessive clearance causes oil consumption and poor sealing.

Cylinder head bolt tightening follows the manual's sequence from the center outward in stages; aluminum heads commonly require clean, lightly oiled threads.

Crankshaft runout is checked with V-blocks and a dial indicator; out-of-spec runout causes vibration and main bearing wear.

Cam chain timing: align the cam sprocket mark with the head surface and the crank mark with the case mark at TDC before installing the tensioner.

Carburetor circuits: pilot (idle) circuit controls low throttle, needle/jet controls mid-range, main jet controls high throttle; the choke enriches cold starts.

Float level is set to the manual's specified height; too high floods and rich-fouls, too low causes lean surge and hard starting.

Air-fuel ratio for gasoline stoichiometric combustion is about 14.7:1 by mass; richer than about 12.5:1 or leaner than about 16:1 affects power and emissions.

Idle mixture screw baseline: turn in gently to seat, then back out the manual's specified turns (commonly 1.5-2.5) and adjust for the highest steady idle.

CDI ignition uses a capacitor discharged through the coil by a trigger signal; a failed pickup coil or CDI unit gives no spark or weak spark.

Ignition timing is set at the specified rpm with a timing light; too advanced causes knock, too retarded causes overheating and power loss.

Spark plug heat range: a hotter plug runs hotter and resists fouling; a colder plug resists pre-ignition in high-load engines.

Exhaust back pressure matters: a restricted muffler or clogged catalytic converter causes power loss; an open pipe leans the mixture and increases noise.

Two-stroke exhaust expansion chamber tuning affects scavenging; exhaust leaks at the flange cause lean running and popping on deceleration.

Clutch free play is measured at the lever or cable; too little causes slipping, too much causes incomplete disengagement and hard shifting.

Wet clutch plates are checked for friction material thickness, warpage on a flat plate with a feeler gauge, and glazing or contamination from wrong oil.

Clutch slip test: hold the brake in gear and release the clutch; engine rpm rising without movement indicates worn plates or weak springs.

Manual transmission shifting problems: check clutch adjustment first, then shift fork wear, bent shift shaft, and detent/spring condition.

Final drive ratio = driven sprocket teeth ÷ drive sprocket teeth; a larger rear or smaller front sprocket increases torque and lowers top speed.

Chain alignment is checked with a straightedge or alignment tool along the sprocket faces; misalignment causes rapid wear and thrown chains.

Belt drive tension is set by the manual's deflection specification at a specified force; too tight damages bearings, too loose causes slip and tooth wear.

Shaft drive final drive oil is changed per interval; whine or metal on the drain plug magnet indicates bearing or gear wear.

Automatic CVT scooters: worn rollers, belt width below limit, and contaminated clutch shoes cause poor acceleration and slipping.

Job order record should contain customer and unit details, complaint, diagnosis, work performed, parts used, labor hours, technician name, and date.

Parts cost = unit price × quantity; add applicable tax and shop supply or disposal fees separately and clearly on the estimate.

Labor cost = labor hours × labor rate; use the manufacturer's flat-rate time where available rather than guessing.

Estimate total = parts + labor + applicable taxes and fees; present a written estimate and obtain customer approval before exceeding it.

Cost variance = actual cost − estimated cost; a positive variance is over budget and should be explained in the report.

Service history retention supports warranty claims and repeat diagnosis; record mileage or hour meter reading at every service.

Depreciation or unit value estimation for repair-or-replace decisions uses parts cost versus a percentage of unit market value as the shop's policy threshold.

Invoice reconciliation: verify parts issued against parts billed and labor hours against the time record before releasing the unit.

Disclose findings honestly: report what was found, what was repaired, and what remains; never bill for work not performed or parts not installed.

Obtain informed consent before additional work; a change order or verbal approval must be documented with date, time, and approver.

Confidentiality rule: customer data, contact details, and vehicle information are not shared outside the transaction without consent.

Explain technical findings in plain language, show the removed part when possible, and state the consequence of deferring a safety-related repair.

Conflict resolution sequence: listen, restate the concern, verify the facts with records, offer options, and document the agreed resolution.

Safety-critical defects (brakes, steering, tires, fuel leaks) must be reported to the customer even if outside the requested job.

Environmental compliance is part of professional conduct: proper waste handling and honest emissions-related repair reporting.

Written warranty terms, turnaround commitments, and pricing must match what was promised; deviations require prior customer agreement.

Personal protective equipment for servicing work: safety glasses or goggles, nitrile gloves for fuel and solvent contact, steel-toe boots, and hearing protection above 85 dB(A).

Exhaust gas carbon monoxide is colorless and odorless; never run an engine in an enclosed space without forced ventilation and a CO monitor.

Battery charging releases hydrogen gas, which is explosive between roughly 4% and 75% concentration in air; charge in a ventilated area with no open flame or spark.

Fuel flash point (gasoline) is about -43 °C, so fuel vapor ignites at ambient temperature; bond and ground containers during transfer to prevent static spark.

Waste segregation rule: used oil, used coolant, solvent sludge, and lead-acid batteries are hazardous and must never enter drains, soil, or general refuse.

Spill response order: stop the source, contain with absorbent, collect into a labeled closed container, then clean the area and record the incident.

Lifting rule: keep the load close, back straight, lift with legs; two-person lift or hoist above roughly 25 kg for a single worker.

Fire extinguisher selection: Class B (CO2 or dry chemical) for fuel and solvent fires; never water on fuel fires or on live electrical equipment.

Compressed air for cleaning must be below 30 psi (207 kPa) with a chip guard; never point air at skin or use it to clean clothing.

Micrometer reading = barrel main scale + thimble reading; least count on a metric 0.01 mm micrometer is 0.01 mm per thimble division.

Vernier caliper reading = main scale value + (coinciding vernier line × least count); a 0.02 mm caliper has 50 vernier divisions.

Cylinder bore measurement uses a bore gauge or inside micrometer read at three heights (top, middle, bottom) and two axes (parallel and perpendicular to the crankshaft).

Cylinder taper = largest bore minus smallest bore along the axis; out-of-round = maximum minus minimum diameter at the same height.

Torque wrench accuracy is specified at a percentage of full scale (commonly ±4%); store click-type wrenches at the lowest setting to protect the spring.

Feeler gauge measures valve clearance, piston ring end gap, and spark plug gap by selecting the blade that produces light drag.

Dial indicator with magnetic base measures crankshaft runout, shaft end play, and disc/rotor lateral runout; zero the indicator before reading.

Plastigauge measures bearing oil clearance: tighten to spec, disassemble, and compare the crushed strip width to the printed scale.

Torque conversion: 1 kgf·m = 9.807 N·m; 1 lbf·ft = 1.356 N·m; 1 lbf·in = 0.113 N·m.

Engine oil change interval is set by the manufacturer; check level with the bike upright and the dipstick or sight glass per manual procedure, not by guess.

Valve clearance is checked with the engine cold (or per manual) at TDC on the compression stroke; incorrect clearance causes noise, hard starting, or burned valves.

Drive chain slack is measured mid-span between sprockets with the bike on its side stand or as specified; typical free play is 20-30 mm.

Chain wear limit is reached when 20 links (or the manual's span) exceed the specified length; replace chain and sprockets as a set.

Air filter service: foam elements are washed, dried, and oiled; paper elements are tapped or blown from the inside out and replaced when damaged or saturated.

Brake fluid is hygroscopic; flush per interval (commonly every 1-2 years) and never mix DOT 3/4 with DOT 5 silicone or mineral oil systems.

Battery open-circuit voltage approximates state of charge: about 12.6-12.8 V fully charged, 12.4 V at 75%, 12.2 V at 50%, 12.0 V at 25%.

Fastener check sequence: follow the manual's torque pattern (usually crisscross or spiral from center outward) and replace torque-to-yield or damaged fasteners.

Tire check: cold inflation pressure per placard, tread depth minimum 1.6 mm (1/16 in) in the grooves, and sidewall for cracks or age codes.

Diagnostic sequence: verify the complaint, gather symptoms, form a hypothesis, test the simplest and most likely cause first, then confirm the repair restores normal operation.

No-start with no spark: check kill switch, side-stand switch, clutch switch, then battery, ignition coil primary/secondary resistance, and pickup/pulser coil gap.

Voltage drop test: measure from source to load under load; more than about 0.5 V drop on a starter circuit indicates high resistance in cable or connection.

Ohm's law: V = I × R; power P = V × I = I²R. A 12 V circuit drawing 2 A dissipates 24 W and has 6 Ω resistance.

Charging system check: battery voltage should rise to roughly 13.5-14.5 V at mid-rpm with lights on; low or absent rise points to stator, regulator/rectifier, or wiring.

Compression test: throttle wide open, engine warm, spin until gauge peaks; low reading that improves with oil added suggests worn rings, not valves.

Leak-down test: apply regulated air at TDC compression; air from the exhaust = exhaust valve, from the intake = intake valve, from the dipstick = rings.

Spark plug reading: black soot = rich mixture or weak ignition; white/blistered = lean or overheating; tan/gray = normal combustion.

Fuel system fault isolation: confirm fuel reaches the float bowl or injector, then check float level, jet/passage cleanliness, and air leaks at the intake boot.

Cylinder wear limits: compare measured bore to the manual's standard and service limit; rebore or replace when taper, out-of-round, or wear exceeds limit.

Piston-to-cylinder clearance is measured at the piston skirt, 90° to the pin, at a specified height; too tight seizes, too loose causes slap and blow-by.

Ring end gap is checked by squaring the ring in the bore with a piston; too small a gap causes ring breakage from thermal expansion.

Ring installation: compression rings with the marked side up, gaps staggered about 120° apart, and the oil ring expander ends butted, not overlapped.

Valve seat contact should be centered on the valve face, typically 1-1.5 mm wide; grind or cut to spec and lap, then check with Prussian blue.

Valve stem-to-guide clearance is measured with a dial gauge or by comparing stem OD to guide ID; excessive clearance causes oil consumption and poor sealing.

Cylinder head bolt tightening follows the manual's sequence from the center outward in stages; aluminum heads commonly require clean, lightly oiled threads.

Crankshaft runout is checked with V-blocks and a dial indicator; out-of-spec runout causes vibration and main bearing wear.

Cam chain timing: align the cam sprocket mark with the head surface and the crank mark with the case mark at TDC before installing the tensioner.

Carburetor circuits: pilot (idle) circuit controls low throttle, needle/jet controls mid-range, main jet controls high throttle; the choke enriches cold starts.

Float level is set to the manual's specified height; too high floods and rich-fouls, too low causes lean surge and hard starting.

Air-fuel ratio for gasoline stoichiometric combustion is about 14.7:1 by mass; richer than about 12.5:1 or leaner than about 16:1 affects power and emissions.

Idle mixture screw baseline: turn in gently to seat, then back out the manual's specified turns (commonly 1.5-2.5) and adjust for the highest steady idle.

CDI ignition uses a capacitor discharged through the coil by a trigger signal; a failed pickup coil or CDI unit gives no spark or weak spark.

Ignition timing is set at the specified rpm with a timing light; too advanced causes knock, too retarded causes overheating and power loss.

Spark plug heat range: a hotter plug runs hotter and resists fouling; a colder plug resists pre-ignition in high-load engines.

Exhaust back pressure matters: a restricted muffler or clogged catalytic converter causes power loss; an open pipe leans the mixture and increases noise.

Two-stroke exhaust expansion chamber tuning affects scavenging; exhaust leaks at the flange cause lean running and popping on deceleration.

Clutch free play is measured at the lever or cable; too little causes slipping, too much causes incomplete disengagement and hard shifting.

Wet clutch plates are checked for friction material thickness, warpage on a flat plate with a feeler gauge, and glazing or contamination from wrong oil.

Clutch slip test: hold the brake in gear and release the clutch; engine rpm rising without movement indicates worn plates or weak springs.

Manual transmission shifting problems: check clutch adjustment first, then shift fork wear, bent shift shaft, and detent/spring condition.

Final drive ratio = driven sprocket teeth ÷ drive sprocket teeth; a larger rear or smaller front sprocket increases torque and lowers top speed.

Chain alignment is checked with a straightedge or alignment tool along the sprocket faces; misalignment causes rapid wear and thrown chains.

Belt drive tension is set by the manual's deflection specification at a specified force; too tight damages bearings, too loose causes slip and tooth wear.

Shaft drive final drive oil is changed per interval; whine or metal on the drain plug magnet indicates bearing or gear wear.

Automatic CVT scooters: worn rollers, belt width below limit, and contaminated clutch shoes cause poor acceleration and slipping.

Job order record should contain customer and unit details, complaint, diagnosis, work performed, parts used, labor hours, technician name, and date.

Parts cost = unit price × quantity; add applicable tax and shop supply or disposal fees separately and clearly on the estimate.

Labor cost = labor hours × labor rate; use the manufacturer's flat-rate time where available rather than guessing.

Estimate total = parts + labor + applicable taxes and fees; present a written estimate and obtain customer approval before exceeding it.

Cost variance = actual cost − estimated cost; a positive variance is over budget and should be explained in the report.

Service history retention supports warranty claims and repeat diagnosis; record mileage or hour meter reading at every service.

Depreciation or unit value estimation for repair-or-replace decisions uses parts cost versus a percentage of unit market value as the shop's policy threshold.

Invoice reconciliation: verify parts issued against parts billed and labor hours against the time record before releasing the unit.

Disclose findings honestly: report what was found, what was repaired, and what remains; never bill for work not performed or parts not installed.

Obtain informed consent before additional work; a change order or verbal approval must be documented with date, time, and approver.

Confidentiality rule: customer data, contact details, and vehicle information are not shared outside the transaction without consent.

Explain technical findings in plain language, show the removed part when possible, and state the consequence of deferring a safety-related repair.

Conflict resolution sequence: listen, restate the concern, verify the facts with records, offer options, and document the agreed resolution.

Safety-critical defects (brakes, steering, tires, fuel leaks) must be reported to the customer even if outside the requested job.

Environmental compliance is part of professional conduct: proper waste handling and honest emissions-related repair reporting.

Written warranty terms, turnaround commitments, and pricing must match what was promised; deviations require prior customer agreement.