Market Position:
The KTM 85sx and 105sx are highly regarded in the youth motocross segment, known for their performance and race-oriented design. This manual serves riders and mechanics aiming to maintain or restore these competitive machines.
Competitive Analysis:
Competes directly with models from brands like Yamaha (YZ85), Kawasaki (KX85), and Suzuki (RM85). The KTMs often differentiate themselves with European engineering and a focus on aggressive power delivery.
Key Features:
Factory-level technical information, comprehensive coverage of critical components (engine, suspension), and detailed procedures for common maintenance and repair tasks.
Engine:
Complete engine tear down, rebuild, troubleshooting, specifications.
Transmission:
Gearbox inspection, repair, and maintenance.
Suspension Front:
Front fork rebuild, maintenance, fluid specifications, assembly.
Suspension Rear:
Rear shock absorber rebuild, maintenance, charging, linkage system.
Fuel System:
Carburetor (jetting, cleaning, adjustment), fuel lines, fuel tank.
Electrical System:
Ignition system, stator, magneto, wiring diagrams, switches.
Brakes:
Front and rear brake systems, caliper service, pad replacement, fluid checks.
Bodywork And Plastics:
Panel removal and installation, fender maintenance.
Wheels And Tires:
Tire pressure, wheel bearing service, spoke tension.
Cooling System:
Radiator maintenance, coolant type, flushing procedures.
Exhaust System:
Muffler and pipe inspection.
Clutch:
Clutch operation, maintenance, and adjustments.
Maintenance:
Scheduled maintenance, fluid changes, filter replacements, lubrication.
Repair:
Complete engine, transmission, suspension, and chassis repairs.
Rebuild:
Detailed step-by-step rebuild instructions for major components like the engine, front forks, and rear shock.
Troubleshooting:
Diagnostic charts, common problems and their solutions, error code interpretation (if applicable).
Installation:
Guidance on installing replacement parts and accessories.
Adjustment:
Carburetor mixture screws, throttle cables, clutch levers, chain tension.
Depth:
Comprehensive from basic maintenance to complete engine and suspension overhauls. Includes detailed diagrams and torque specifications for precise assembly.
Engine Type:
Two-stroke, single-cylinder
Displacement 105Sx:
105cc
Bore Stroke 85Sx:
Approx. 47mm x 48.6mm
Bore Stroke 105Sx:
Approx. 52.5mm x 48.6mm
Cooling System:
Liquid-cooled
Ignition System:
Digital CDI
Horsepower Estimate:
Varies by year and specific tuning, typically in the 20-25 HP range for the 85cc.
Torque Estimate:
Not typically quoted in standard specs, but designed for strong low-to-mid range power.
Carburetor Model:
Mikuni VM28 (common for these years, specific model may vary slightly)
Fuel Type:
Unleaded gasoline with appropriate two-stroke oil pre-mix
Premix Ratio:
Typically 40:1 or 50:1, check specific manual recommendations.
Oil Change Interval:
Gearbox oil: Recommended every 10-15 hours of riding. Refer to manual for exact procedure and oil type.
Air Filter Cleaning:
Clean and re-oil after every few rides or as needed, depending on conditions.
Spark Plug Replacement:
Inspect regularly, replace as needed based on condition. NGK BR10EG or equivalent.
Top End Rebuild:
Recommended between 40-60 hours of riding for optimal performance and reliability.
Gearbox Oil Type:
SAE 80 or 85W motocross gear oil. Check manual for specific API GL classification (e.g., GL-4).
Coolant Type:
High-quality ethylene glycol based coolant with corrosion inhibitors. Typically a 50/50 mix with distilled water.
Fork Oil Type:
Specific viscosity and volume for front forks (e.g., WP Suspension Fork Oil 7.5W or equivalent). Check manual for precise specs.
Brake Fluid Type:
DOT 4 or DOT 5.1 hydraulic brake fluid.
Known Issues:
Common wear items include piston rings, clutch plates, and wheel bearings. Suspension seals can also require periodic replacement. Proper maintenance is key to preventing premature wear.
Carburetor Tuning:
Can be sensitive to altitude and temperature changes, requiring occasional jetting adjustments.
Brand Heritage:
KTM, 'Ready to Race', has a strong heritage in off-road racing, particularly motocross and enduro. This philosophy is evident in the performance-oriented design of the 85sx and 105sx models.
Model Evolution:
The 85sx has been a staple in KTM's youth lineup, evolving through various chassis and engine updates to maintain its competitive edge. The 105sx was a variant aimed at riders needing a slight displacement advantage.
Production Years Covered:
2004-2009
📄 Technical Specifications
Torque Specs Included:
Yes, detailed torque specifications for critical fasteners (e.g., cylinder head, crankcase, suspension components).
Part Diagrams Included:
Yes, comprehensive exploded view diagrams for all major assemblies.
Wiring Schematics Included:
Yes, electrical system diagrams for troubleshooting.
Target Audience:
Enthusiast riders, home mechanics, and professional service technicians working on KTM 85sx/105sx models.
Value Proposition:
Provides factory-accurate procedures and specifications essential for maintaining the performance and longevity of these high-performance youth motocross bikes, saving time and money on repairs and upkeep.
Completeness:
Offers a complete guide covering all aspects of service, repair, and maintenance, including specialized sections for engine and suspension rebuilds.
