Positioning:
The BMW R90 series represented BMW's entry into the larger displacement motorcycle market, known for its robust engineering and touring capabilities.
Competitors:
Competed with other European and Japanese motorcycles offering similar displacement and touring features, though BMW's shaft drive and boxer engine configuration offered unique advantages.
Distinctive Features:
Shaft drive, air-cooled flat-twin boxer engine, robust build quality, comfortable ergonomics for long-distance riding, particularly the R90S with its sportier fairing and dual front discs.
Engine:
Detailed disassembly, assembly, inspection, and overhaul procedures for the BMW flat-twin boxer engine.
Fuel System:
Carburetor service (Dell'Orto PHM 40 CS), fuel tank, fuel lines, fuel pump, fuel filter.
Ignition System:
Points, condenser, ignition coils, spark plugs, timing adjustments, electronic ignition options (if applicable to '83).
Transmission:
Gearbox inspection, lubrication, repair, clutch operation and adjustment, final drive assembly.
Electrical System:
Wiring diagrams, battery, charging system (alternator, regulator), lighting, starter motor, instrument cluster, horn.
Brakes:
Front and rear brake systems, brake fluid specifications, caliper service, master cylinder, brake lines, pad replacement.
Suspension Steering:
Front forks (oil change, seal replacement), rear shock absorbers, swingarm, steering head bearings, wheel bearings.
Chassis Bodywork:
Frame inspection, seat, fuel tank mounting, fenders, exhaust system, general body component removal/installation.
Maintenance:
Routine servicing, oil changes, filter replacements, lubrication points, chain adjustment, spark plug replacement.
Troubleshooting:
Diagnostic guides for common running issues, electrical faults, starting problems.
Repair:
Step-by-step instructions for engine rebuild, transmission overhaul, brake system repair, electrical component replacement.
Adjustments:
Carburetor synchronization and tuning, ignition timing, clutch and throttle cable adjustments, valve clearance checks.
Wheel Service:
Wheel bearing replacement, spoke tensioning (if applicable), tire mounting and balancing.
Exhaust System Repair:
Inspection, gasket replacement, muffler repair or replacement.
Body Panel Removal:
Detailed procedures for removing fuel tank, side covers, fenders, seat, and headlight assembly.
Depth:
Comprehensive, suitable for experienced home mechanics and professional technicians. Covers from basic maintenance to complete engine and transmission rebuilds.
Specific Rebuilds:
Complete engine rebuild including piston and cylinder service, crankshaft inspection, camshaft and valve train overhaul.
Diagnostic Charts:
Troubleshooting charts correlating symptoms with potential causes and corrective actions for engine, electrical, and chassis issues.
Engine Type:
Air-cooled, four-stroke, flat-twin boxer
Bore X Stroke:
90 mm x 70.6 mm
Compression Ratio:
9.5:1 (R90S), 8.2:1 (R90/6)
Horsepower:
67 hp (49 kW) at 7,000 rpm (R90S), 55 hp (40 kW) at 6,200 rpm (R90/6)
Torque:
77 Nm (57 lb-ft) at 5,500 rpm (R90S), 75 Nm (55 lb-ft) at 5,000 rpm (R90/6)
Carburetors:
2 x Dell'Orto PHM 40 CS (R90S), 2 x Bing 32mm (R90/6)
Fuel Capacity:
24 liters (6.3 US gal)
Crash Test Ratings:
N/A (Motorcycle, pre-dates standardized motorcycle crash testing)
Braking:
Dual front disc brakes (R90S), Single front disc brake (R90/6), Rear drum brake. Hydraulic actuation.
Lighting:
Halogen headlight, taillight, brake light, turn signals.
Frame:
Steel tube duplex cradle frame providing robust structural integrity.
Oil Change Interval:
Every 5,000 km (3,000 miles) or annually
Valve Adjustment Interval:
Every 10,000 km (6,000 miles)
Spark Plug Replacement Interval:
Every 10,000 km (6,000 miles)
Engine Oil Type:
SAE 20W-50 or SAE 15W-40 (API SE/SF recommended for modern equivalents)
Engine Oil Capacity:
2.5 liters (2.6 US qt) with filter change
Transmission Oil Type:
SAE 80W-90 GL-4 Gear Oil
Final Drive Oil Type:
SAE 80W-90 GL-5 Gear Oil
Brake Fluid Type:
DOT 3 or DOT 4 hydraulic fluid
Fork Oil Type:
Telescopic fork oil (e.g., SAE 15W or equivalent)
Common Wear Items:
Clutch friction plates, swingarm bearings, steering head bearings, fork seals, valve guide wear.
Electrical Concerns:
Age-related degradation of wiring insulation, starter motor brushes, and diode boards/regulators.
Carburetor Issues:
Diaphragm leaks in Dell'Orto carbs, worn throttle shafts, and synchronization drift.
Heritage:
BMW Motorrad has a long history dating back to the early 20th century, renowned for engineering excellence, reliability, and distinctive boxer engines.
Predecessors:
Evolved from earlier R75/5 and R80 models, building upon the established air-cooled boxer platform.
Successors:
Led to models like the R100 series, further refining the boxer engine and chassis designs.
Production Years:
1973-1976 (R90/6 and R90S)
Manufacturing Location:
Berlin, Germany (Spandau plant)
