Market Position:
The BMW R90 series (specifically R90/6 and R90S) were high-performance touring motorcycles in the 1970s, positioned as premium, comfortable, and capable machines for long-distance riding and sport touring. They competed with other large displacement European and Japanese motorcycles of the era.
Competitors:
Competed with models like the Moto Guzzi V7 Sport, Kawasaki Z900, Honda CB750F, and Ducati 900SS.
Key Features:
Torquey 900cc air-cooled boxer twin engine, shaft drive, comfortable riding position, excellent build quality, touring capability, and the iconic R90S featured distinctive styling and sportier performance.
Covered Years:
1978-1996 (Specific R90 models within this range, likely implying related or successor models that share components/procedures, as R90 production ended in 1976. This suggests a broad service manual covering airhead boxer engine platforms.)
Note On Years:
While the title lists 1978-1996, the core R90 models were produced until 1976. This coverage likely extends to the general 'airhead' boxer platform that includes models with shared mechanical principles and components through the 1980s and into the early 1990s, offering a broader service manual for enthusiasts working on this engine architecture.
Estimated Page Count:
Comprehensive (Exact page count not provided, but typical for such extensive coverage would be 500+ pages)
Manual Type:
Repair Service Manual
Engine:
Full overhaul, disassembly, assembly, tuning, troubleshooting for the 900cc boxer twin engine (Type 247).
Transmission:
5-speed gearbox service, repair, and maintenance.
Drivetrain:
Driveshaft, final drive, clutch service and repair.
Fuel System:
Carburetor (likely Dell'Orto or Bing) overhaul, adjustment, and troubleshooting; fuel tank and lines.
Ignition System:
Points ignition, ignition timing, coil, spark plug service.
Electrical System:
Wiring diagrams, charging system (alternator/generator), lighting, starter motor, battery maintenance.
Brakes:
Front and rear brake systems (drum and possibly disc depending on specific R90 sub-model or variant covered), hydraulic components, adjustment.
Suspension:
Front fork (telescopic), rear swingarm, shock absorber service and adjustment.
Bodywork:
Frame, fenders, fuel tank, seat, minor body panel repair and maintenance.
Wheel Bearings:
Front and rear wheel bearing service and replacement.
Frame Chassis:
Frame integrity checks, steering head bearing service, chassis alignment.
Instruments Controls:
Dashboard instruments, handlebar controls, and cable adjustments.
Maintenance:
Regular service checks, oil changes, filter replacements, lubrication points, brake adjustments, tire pressure checks.
Troubleshooting:
Diagnostic procedures for common performance issues, electrical faults, starting problems, and mechanical noises.
Repair:
Step-by-step instructions for engine rebuilds, transmission repairs, clutch replacement, carburetor overhaul, brake system overhauls, and suspension component replacement.
Disassembly Assembly:
Detailed guides for dismantling and reassembling all major components.
Specifications Data:
Torque specifications, clearances, fluid capacities, and other critical technical data.
Wiring Diagrams:
Comprehensive electrical schematics for troubleshooting and repairs.
Electrical Troubleshooting:
Systematic fault finding for lighting, ignition, charging, and starting circuits.
Depth:
Comprehensive, covering basic owner maintenance through to full engine and transmission rebuilds. Suitable for home mechanics and professional technicians.
Manual Type Detail:
This is a comprehensive service manual providing detailed instructions for maintenance, troubleshooting, and repair of the BMW R90 series motorcycles. It is designed to guide users through tasks ranging from routine servicing to complete engine and gearbox overhauls.
Engine Type:
Air-cooled, four-stroke, boxer twin (Type 247)
Displacement:
897 cc (54.7 cu in)
Bore X Stroke:
90 mm x 70.6 mm (3.54 in x 2.78 in)
Compression Ratio:
9.5:1 (R90/6), 9.5:1 (R90S - though some sources cite 8.2:1 for earlier models)
Valve Train:
OHV, 2 valves per cylinder, pushrod actuated
Engine Cooling:
Air-cooled
Fuel Delivery:
Carburetor
Horsepower Rating:
R90/6: 60 hp (45 kW) @ 6500 rpm; R90S: 67 hp (50 kW) @ 7000 rpm
Torque Rating:
R90/6: 73 Nm (54 lb-ft) @ 5500 rpm; R90S: 75 Nm (55 lb-ft) @ 5500 rpm
Carburetors:
R90/6: 2 x Bing 32mm CV; R90S: 2 x Dell'Orto 36mm PHM
Fuel Type:
Unleaded gasoline, minimum 91 RON
Length:
Approx. 2180 mm (85.8 in) for R90/6
Width:
Approx. 840 mm (33.1 in) for R90/6
Height:
Approx. 1200 mm (47.2 in) for R90/6
Dry Weight:
R90/6: Approx. 200 kg (441 lbs); R90S: Approx. 200 kg (441 lbs)
Gross Vehicle Weight Rating:
Not officially specified, but typically around 380-400 kg
Fuel Capacity:
24 liters (6.3 US gal)
Oil Change Interval:
Every 5,000 km (3,000 miles) or annually, whichever comes first. Check level more frequently.
Major Service Interval:
Every 10,000 km (6,000 miles) for valve adjustment, timing checks, and carb synchronization.
Spark Plug Replacement:
Every 10,000 km (6,000 miles)
Engine Oil Type:
API SG or higher, SAE 20W-40 or 20W-50 recommended (check manual for specific recommendations).
Engine Oil Capacity:
Approx. 2.5 liters (2.6 US qt) with filter change.
Transmission Oil Type:
SAE 80W-90 API GL-5 gear oil.
Transmission Oil Capacity:
Approx. 0.8 liters (0.8 US qt)
Final Drive Oil Type:
SAE 80W-90 API GL-5 gear oil.
Final Drive Oil Capacity:
Approx. 0.2 liters (0.2 US qt)
Brake Fluid Type:
DOT 4 hydraulic fluid (for disc brakes).
Fork Oil Type:
SAE 10W or 15W fork oil (check specific model/year recommendation).
Known Issues:
Worn clutch splines, gearbox input shaft seal leaks, starter clutch wear, aging electrical components, carburetor float issues, fork seal leaks, potential main bearing wear on high-mileage engines.
Common Procedures:
Valve clearance adjustment, carburetor synchronization and tuning, checking and adjusting final drive backlash.
Brand Heritage:
BMW Motorrad has a long history of producing robust, reliable motorcycles, particularly known for their boxer twin engines and shaft drive, emphasizing engineering excellence and durability.
Model Evolution:
The R90 series was an evolution of BMW's successful /5 and /6 series. The R90/6 was the standard touring model, while the R90S was a sportier variant introduced in 1973, featuring dual front disc brakes, higher compression, hotter camshafts, and distinctive cafe racer styling (like the bikini fairing and sport seat), often considered a landmark in sportbike development.
Production Period:
R90/6: 1973-1976; R90S: 1973-1976
Manufacturing Location:
Berlin, Germany (Spandau plant)
Production Numbers:
R90/6: Approximately 16,400 units; R90S: Approximately 7,900 units
