Positioning:
The Yamaha YZ85 is a highly competitive junior motocross bike, renowned for its performance and reliability in its class. This manual is essential for owners and mechanics seeking to maintain and repair these potent machines.
Competitors:
Competes directly with models like the Kawasaki KX85, Suzuki RM85, and KTM 85 SX of the same era.
Vehicle Strengths:
Powerful two-stroke engine, agile chassis, capable suspension, race-proven design.
Purpose:
To provide detailed instructions for the diagnosis, maintenance, repair, and overhaul of the Yamaha YZ85 for the specified model years.
Primary Coverage:
Service, Repair, Workshop
Secondary Coverage:
Maintenance, Troubleshooting, Diagnostics, Overhaul, Reassembly
Estimated Page Count:
300-400 (typical for this era and type of manual)
Type:
Factory Service Manual / Workshop Manual
Format:
Digital (likely PDF)
Engine:
Top-end rebuild (piston, rings, cylinder, head), bottom-end rebuild (crankshaft, bearings, seals), cooling system (radiator, hoses, water pump), lubrication system, carburetor tuning and overhaul, exhaust system.
Transmission:
Clutch operation and adjustment, gear shifting mechanism, transmission disassembly and reassembly, gear inspection, bearing replacement.
Chassis:
Frame inspection and repair, suspension systems (front fork, rear shock absorber), swingarm and linkage maintenance, steering system maintenance and bearing replacement, brake system overhaul (front and rear), wheel and tire maintenance, chain and sprocket inspection and replacement.
Electrical:
Ignition system troubleshooting and testing, lighting system, wiring diagrams, CDI unit, spark plug diagnosis.
Maintenance:
Pre-ride inspection, oil changes, filter cleaning/replacement, chain lubrication and adjustment, spark plug replacement, brake pad inspection/replacement, coolant checks, general cleaning and lubrication.
Repair:
Engine rebuilding (full), transmission overhauls, carburetor jetting and rebuilding, suspension servicing and re-valving, brake caliper and master cylinder rebuilds, wheel bearing replacement, clutch replacement, exhaust system repair/replacement.
Troubleshooting:
Diagnostic flowcharts for common issues (e.g., no start, poor running, clutch slip), electrical system diagnosis, carburetor performance issues.
Special Tools:
Identification and use of specialized tools required for specific repairs (e.g., flywheel puller, clutch holder tool, specialized bearing drivers).
Depth:
Comprehensive, covering everything from routine maintenance to complete engine and transmission overhauls. Includes detailed disassembly and reassembly instructions with torque specifications.
Type:
Liquid-cooled, 2-stroke, Reed valve, Yamaha Power Valve System (YPVS)
Bore X Stroke:
47.5 x 47.0 mm
Compression Ratio:
8.6:1 (typical, check manual for exact spec)
Horsepower:
Approx. 21-23 HP (at crankshaft, typical for class)
Torque:
Approx. 7-8 lb-ft (at crankshaft, typical for class)
Carburetor:
Mikuni VM28SS
Fuel Type:
Unleaded gasoline (min 91 octane recommended)
Fuel Mixture:
2-stroke oil premix (50:1 or as specified in manual)
Ignition System:
CDI (Capacitor Discharge Ignition)
Cooling System:
Liquid-cooled
Coolant Type:
Yamaha-recommended coolant (50/50 mix of antifreeze and distilled water)
Type:
6-speed constant mesh
Clutch Type:
Wet, multiple-disc
Gear Ratios:
Detailed ratios for each gear will be present in the manual.
Transmission Oil Type:
Yamalube 10W-40 or equivalent API SE, SF, SG classification (check manual for exact specification)
Transmission Oil Capacity:
Approx. 0.70 L (0.74 US qt) (check manual for exact specification)
Oil Change Interval:
Check transmission oil level every ride, change as per manual recommendation (e.g., every 10-15 hours of operation or annually).
Air Filter Cleaning:
Clean after every few rides or as needed, depending on conditions. Replace element as per manual.
Spark Plug Replacement:
Inspect regularly, replace when fouled or worn (check manual for recommended interval).
Chain And Sprocket Maintenance:
Lubricate and check tension before every ride. Replace worn components as a set.
Top End Rebuild:
Recommended every 25-50 hours of hard use, or when performance degrades. Manual will provide specific wear limits for piston and cylinder.
Fork Oil Type:
Yamalube Fork Oil 01 (or equivalent SAE 5W or 7.5W fork oil, check manual for exact specification)
Fork Oil Quantity:
Approx. 300 cc (left fork), 320 cc (right fork) (check manual for exact specification)
Common Wear Items:
Clutch plates, piston rings, spark plugs, chain and sprockets, wheel bearings, fork seals, swingarm bushings.
Typical Problems:
Carburetor jetting issues due to altitude or temperature changes, clutch fade from hard use, suspension wear over time, overheating if coolant levels are low.
