Yamaha YZ125(R)/LC Owner’s Service Manual, 2002–2005 (P/N 5UN-28199-30)

Yamaha’s YZ125(R)/LC Owner’s Service Manual (P/N 5UN-28199-30) covers the YZ125LC for Europe, the YZ125R for the USA, and the YZ125(R) for Canada, Australia, New Zealand, and South Africa.

Searchable Text, Bookmarks, and Languages

Text search and diagram detail: The main text is searchable. Chapter bookmarks open the English or multilingual contents pages. The ignition wiring diagram is on the English electrical page, with French, German, and Italian legends on the facing page. Wire codes and connector labels are legible, and zooming makes the crowded areas easier to follow.

The download contains one printable 565-page PDF with English, French, German, and Italian text. The total includes two cover pages and two memo pages.

Engine Repair, Chassis Service, and Race Tuning

These selected topics give a view of the manual’s service coverage. It also includes pre-operation checks and starting and break-in procedures.

• Engine repair: Step-by-step instructions cover crankcase separation and cylinder and piston service. The engine chapter also covers engine removal, crankshaft inspection, power-valve service, and YPVS governor disassembly.
• Clutch and transmission: Inspect the clutch pack and service the primary drive, kickstarter, and shift shaft. The manual shows how to remove and assemble the transmission, shift cam, and shift forks.
• Fuel and cooling: Carburetor and reed-valve service, fuel-level adjustment, radiator-cap and cooling-system pressure tests, and water-pump disassembly and seal replacement.
• Brakes and chassis: Front and rear caliper and master-cylinder service, brake bleeding, wheel-bearing replacement, handlebar service, steering-head adjustment, and swingarm linkage inspection.
• Suspension and tuning: Front-fork oil-seal replacement, damper-rod inspection, rear-shock spring and bearing service, carburetor tuning charts, and suspension symptom charts.
• Ignition diagnosis: Component locations, a wiring diagram, a no-spark flowchart, coil-resistance tests, and ignition-timing checks.

Owners can use the operating and routine-maintenance sections. Internal repair work is suited to mechanics familiar with two-stroke engines and the specified measuring and service tools.

Engine Repair and Assembly References

The seven chapters use exploded assembly views, job instruction charts, sectional views, and inspection notes that link component condition to the required action. Torque-check illustrations and component-specific tables cover engine, frame, and suspension fasteners.

Piston and crankshaft work: The matching chart pairs cylinder size groups with piston markings and colors, helping you identify the correct replacement piston before assembly. Cylinder inspection includes bore and wear limits. Yamaha prohibits reboring the cylinder. Crankshaft removal calls for crankcase separator YU-1135-A / 90890-01135.

Transmission and clutch: Gear-dog and shift-fork checks are backed by assembly illustrations showing gear order, fork orientation, and circlip position. The clutch section identifies the friction plates used at each end of the pack by their surface pattern.

Carburetor, Cooling, and Race Preparation

The Mikuni carburetor section covers float-level measurement, needle-valve inspection, reed-valve checks, and reassembly. The venturi block and main nozzle stay assembled during service. The main nozzle is nonreplaceable.

Throttle-opening charts and separate jet-needle guidance for European versions help match adjustments to running symptoms. The tuning chapter also covers spark plug heat range, optional ignition rotors, and sprocket selection. Routine upkeep includes race-based maintenance schedules, air-filter cleaning, and silencer repacking.

Water-pump assembly notes flag a specific risk during impeller-shaft installation. The oil-seal lip can be damaged or its spring displaced.

Fork, Rear Shock, and Chassis Service

Fork disassembly views identify the seals, bushings, base valve, and damper rod. The assembly section specifies fork seal driver YM-01442 / 90890-01442 and explains air removal and oil-level measurement. A damper rod that drops into the inner tube can damage the valve inside.

The suspension specifications distinguish European spring designs and baseline damping settings. The tuning charts connect symptoms such as bottoming, harshness, and poor grip with front and rear suspension adjustments.

Rear-shock service covers removal, spring replacement, mounting bearings, and external adjustments. Yamaha warns against opening the pressurized cylinder or nitrogen reservoir and specifies replacing the shock assembly if it leaks oil or gas.

Steering and swingarm sections cover bearing inspection and installation, with separate notes for the linkage’s Polylube bearings. Brake coverage includes piston seals, master-cylinder cups, hose routing, and leak checks.

Ignition Fault Tracing

The no-spark flowchart takes you through wiring connections, the engine-stop button, the ignition coil, the plug cap, and the CDI magneto before CDI-unit replacement. Wiring color codes and connector views help you identify the leads for the resistance checks.

A Preview of Piston, Fastener, and Ignition Data

For cylinder and piston inspection, standard piston-to-cylinder clearance is 0.040–0.045 mm, with a service limit of 0.1 mm. The cylinder-head nuts have a final torque of 28 Nm (20 ft-lb) and are tightened in stages in a crisscross pattern.

For ignition diagnosis, the CDI magneto’s pickup coil is specified at 248–372 ohms at 20°C (68°F).