Target Audience:
        
        
            BMW R90 owners, mechanics, restorers, enthusiasts
        
     
    
        
            Value Proposition:
        
        
            Enables owners to perform all necessary maintenance and repairs, reducing reliance on costly service centers and preserving vehicle value.
        
     
    
    
        
            Competitors:
        
        
            Haynes, Clymer, or other unofficial repair manuals (often less detailed or accurate)
        
     
    
    
        
            Feature 1:
        
        
            Comprehensive diagnostic information specific to the R90 model.
        
     
    
        
            Feature 2:
        
        
            Detailed exploded diagrams and step-by-step repair instructions.
        
     
    
        
            Feature 3:
        
        
            Crucial technical specifications and torque values.
        
     
    
        
            Feature 4:
        
        
            Wiring schematics for accurate electrical system troubleshooting.
        
     
 
    
    
    
        
            Primary Coverage:
        
        
            BMW R90 (1981 Model Year)
        
     
    
        
            Engine Coverage:
        
        
            All R90 engine variants
        
     
    
        
            Chassis Coverage:
        
        
            Frame, suspension, wheels, brakes
        
     
    
        
            Electrical Coverage:
        
        
            Wiring diagrams, lighting, ignition, starting, charging systems
        
     
    
        
            Bodywork Coverage:
        
        
            Body panels, fairings, seat, fuel tank, trim
        
     
    
        
            Maintenance Coverage:
        
        
            Scheduled maintenance, fluid changes, adjustments
        
     
    
        
            Repair Coverage:
        
        
            Engine rebuild, transmission overhaul, brake system repair, electrical troubleshooting
        
     
    
        
            Troubleshooting Coverage:
        
        
            Diagnostic procedures, common issues and solutions
        
     
    
    
        
            Estimated Page Count:
        
        
            Likely 300-500 pages (typical for comprehensive service manuals of this era)
        
     
    
    
        
            Type:
        
        
            Full Service and Repair Manual
        
     
    
    
    
    
        
            Format:
        
        
            Digital (likely PDF)
        
     
 
    
    
    
        
            Engine Mechanical:
        
        
            Disassembly, inspection, repair, reassembly of all engine components (cylinders, pistons, crankshaft, camshafts, valves, etc.)
        
     
    
        
            Engine Management:
        
        
            Carburetor tuning and rebuilding, ignition system timing and adjustment, spark plug selection and replacement
        
     
    
        
            Transmission Drivetrain:
        
        
            Gearbox operation, clutch service, final drive maintenance and repair
        
     
    
        
            Brakes:
        
        
            Front and rear brake system overhaul, hydraulic fluid service, pad and caliper inspection/replacement
        
     
    
        
            Suspension Steering:
        
        
            Front fork service and seal replacement, rear shock absorber maintenance, steering head bearing adjustment
        
     
    
        
            Electrical System:
        
        
            Detailed wiring diagrams, troubleshooting guides for lights, horn, starter, alternator, battery charging system
        
     
    
        
            Fuel System:
        
        
            Fuel tank inspection, fuel line maintenance, carburetor cleaning and adjustment
        
     
    
        
            Exhaust System:
        
        
            Exhaust pipe and muffler inspection and replacement
        
     
    
        
            Cooling System:
        
        
            N/A (Air-cooled engine)
        
     
    
    
        
            Routine Maintenance:
        
        
            Oil change, filter replacement, chain adjustment, lubrication points
        
     
    
        
            Engine Overhaul:
        
        
            Complete engine teardown and rebuild procedures with specifications
        
     
    
        
            Carburetor Rebuilding:
        
        
            Step-by-step instructions for disassembling, cleaning, and reassembling carburetors
        
     
    
        
            Brake System Service:
        
        
            Bleeding brake lines, replacing brake pads and discs
        
     
    
        
            Electrical Troubleshooting:
        
        
            Fault finding for starting issues, charging system problems, lighting malfunctions
        
     
    
        
            Wheel Wheel Alignment:
        
        
            Spoke tension adjustment, wheel balancing, steering alignment checks
        
     
    
        
            Suspension Adjustment:
        
        
            Front fork oil level and damping adjustments, rear shock preload settings
        
     
    
        
            Bodywork Repair:
        
        
            Minor dent repair, panel alignment, trim piece replacement
        
     
    
    
        
            Depth:
        
        
            Comprehensive (from basic maintenance to full engine rebuilds and diagnostics)
        
     
    
        
            Diagnostic Coverage:
        
        
            Detailed diagnostic procedures, troubleshooting flowcharts
        
     
    
        
            Specification Detail:
        
        
            Torque specifications, clearances, tolerances, fluid capacities, electrical resistance values
        
     
 
    
    
    
        
            Engine Type:
        
        
            Air-cooled, horizontally opposed twin-cylinder boxer engine
        
     
    
        
            Displacement:
        
        
            897 cc (54.7 cubic inches)
        
     
    
        
            Bore X Stroke:
        
        
            90.0 mm x 70.6 mm (3.54 in x 2.78 in)
        
     
    
        
            Compression Ratio:
        
        
            Approximately 8.2:1 (subject to specific market variations)
        
     
    
    
        
            Horsepower:
        
        
            Approximately 60 hp (45 kW) at 6250 rpm (DIN)
        
     
    
        
            Torque:
        
        
            Approximately 76 Nm (56 lb-ft) at 4500 rpm (DIN)
        
     
    
    
        
            Carburetors:
        
        
            Dual Bing constant velocity carburetors (e.g., Bing 32/32/36 or similar, depending on specific R90 variant and market)
        
     
    
        
            Fuel Type:
        
        
            Unleaded gasoline (premium recommended, octane rating as per manual specifications)
        
     
    
    
        
            Ignition Type:
        
        
            Battery-coil ignition with breaker points and centrifugal advance
        
     
    
    
        
            Oil Type:
        
        
            SAE 20W-50 or 10W-40 motorcycle specific engine oil (refer to manual for exact specification and seasonal recommendations)
        
     
    
        
            Oil Capacity:
        
        
            Approximately 2.0 - 2.5 liters (2.1 - 2.6 US quarts) with filter change (refer to manual for precise capacity)
        
     
    
    
        
            Engine Designation:
        
        
            R90 series (specific engine codes may exist, e.g., R90/6, R90S)
        
     
 
    
    
    
        
            Transmission Type:
        
        
            5-speed manual gearbox
        
     
    
    
        
            Optional Transmissions:
        
        
            N/A (Standard fitment for R90)
        
     
    
    
        
            Clutch Type:
        
        
            Single dry plate clutch, hydraulically operated
        
     
    
        
            Drive Type:
        
        
            Shaft drive to rear wheel
        
     
    
    
        
            Gearbox Oil Type:
        
        
            SAE 80W-90 hypoid gear oil (refer to manual for exact specification)
        
     
    
    
        
            Gearbox Oil Capacity:
        
        
            Approximately 0.5 liters (0.5 US quarts) (refer to manual for precise capacity)
        
     
 
    
    
    
        
            Wheelbase:
        
        
            Approximately 1465 mm (57.7 inches) (R90/6)
        
     
    
        
            Length:
        
        
            Approximately 2230 mm (87.8 inches) (R90/6)
        
     
    
    
        
            Dry Weight:
        
        
            Approximately 200-215 kg (441-474 lbs) (depending on specific R90 variant and equipment)
        
     
    
        
            Gross Vehicle Weight Rating:
        
        
            Refer to vehicle's compliance plate/manual
        
     
    
    
        
            Front Tire Size:
        
        
            3.50-18 (e.g., 100/90-18)
        
     
    
        
            Rear Tire Size:
        
        
            4.00-18 (e.g., 110/90-18 or 120/90-18)
        
     
    
        
            Wheel Type:
        
        
            Spoked wheels with either aluminum or chrome rims
        
     
    
        
            Bolt Pattern:
        
        
            N/A (Not applicable for motorcycle wheels)
        
     
 
    
    
    
        
            Safety Ratings:
        
        
            N/A (Motorcycle safety is not rated by typical automotive bodies like NHTSA/Euro NCAP)
        
     
    
    
        
            Braking System:
        
        
            Dual disc front brakes (R90S typically), single disc front (R90/6), drum brake rear.  Hydraulic actuation.
        
     
    
    
        
            Lighting:
        
        
            Halogen headlight, tail light, brake light, turn signals
        
     
    
        
            Mirrors:
        
        
            Dual rear-view mirrors
        
     
 
    
    
    
        
            Infotainment System:
        
        
            N/A (This era of motorcycle predates modern infotainment systems.)
        
     
    
    
        
            Advanced Assistance:
        
        
            N/A (No electronic driver assistance features.)
        
     
    
    
        
            Connectivity Features:
        
        
            N/A (No connectivity features.)
        
     
    
    
        
            Instrument Cluster:
        
        
            Analog speedometer, tachometer, voltmeter (on some models), indicator lights for oil pressure, high beam, turn signals, neutral.
        
     
 
    
    
    
        
            Oil Change Interval:
        
        
            Every 5,000 km (3,000 miles) or annually (refer to manual for precise interval and oil drain plug washer replacement).
        
     
    
        
            Major Service Interval:
        
        
            Every 10,000-15,000 km (6,000-9,000 miles), including valve clearance adjustment, spark plug replacement, and carburetor synchronization.
        
     
    
        
            Valve Clearance Adjustment:
        
        
            Every 5,000 km (3,000 miles) or as specified in the manual (typically 0.15 mm for both intake and exhaust, cold).
        
     
    
    
        
            Brake Fluid Type:
        
        
            DOT 3 or DOT 4 brake fluid (refer to manual for exact specification and flush interval).
        
     
    
        
            Final Drive Oil Type:
        
        
            SAE 80W-90 hypoid gear oil (same as gearbox, refer to manual).
        
     
    
    
        
            Final Drive Oil Capacity:
        
        
            Approximately 0.2 liters (0.2 US quarts) (refer to manual for precise capacity)
        
     
    
    
        
            Common Issue 1:
        
        
            Leaking output shaft seals and transmission output seals due to age and seal degradation.
        
     
    
        
            Common Issue 2:
        
        
            Carburetor float bowl gaskets and O-rings can degrade, leading to fuel leaks or poor running.
        
     
    
        
            Common Issue 3:
        
        
            Wear in the transmission selector drum and lever mechanism can lead to sloppy shifting or difficulty finding neutral.
        
     
    
        
            Common Issue 4:
        
        
            Electrical connections and wiring can corrode over time, leading to intermittent issues with lights, ignition, or charging.
        
     
    
        
            Common Issue 5:
        
        
            Aging rubber components such as fuel lines, intake boots, and fork seals will require replacement.
        
     
    
        
            Common Issue 6:
        
        
            Starter motor brushes may wear out, leading to slow or no engine cranking.
        
     
 
    
    
    
        
            Brand Origin:
        
        
            Bayerische Motoren Werke AG (BMW), Germany
        
     
    
        
            Motorcycle Heritage:
        
        
            BMW has a long and distinguished history in motorcycle manufacturing, dating back to the early 20th century, renowned for engineering excellence and durability.
        
     
    
    
        
            R90 Development:
        
        
            The R90 was part of BMW's airhead boxer motorcycle lineage, evolving from earlier models. The R90/6 and R90S were introduced in 1973 as powerful and sophisticated touring and sport-touring motorcycles.
        
     
    
        
            R90 Variants:
        
        
            Key variants include the R90/6 (standard touring model) and the R90S (sportier version with dual disc brakes, clip-on handlebars, and often different bodywork).
        
     
    
    
        
            Production Period:
        
        
            1973-1976
        
     
    
        
            Production Location:
        
        
            Berlin-Spandau, Germany
        
     
    
        
            Significance:
        
        
            The R90 series was a significant motorcycle for BMW, demonstrating their capability in producing large-displacement, high-performance boxer twins that were also reliable for long-distance travel.
        
     
 
    
    
    
        
            Historical Recognition:
        
        
            The BMW R90 series, particularly the R90S, was critically acclaimed in its time for its performance, handling, and build quality, often considered a benchmark in the sport-touring motorcycle segment.
        
     
    
    
        
            Customer Satisfaction:
        
        
            Consistently high ratings among enthusiasts for reliability and enduring design. Revered for its character and capability.
        
     
    
    
        
            Manufacturing Standards:
        
        
            Produced under BMW's stringent German engineering and manufacturing quality standards of the era.