1973–1976 BMW R90, R90S, R 90/6 Service Manual (P/N 01 99 9 099 421)

Covering the BMW R 60/6, R 75/6, R 90/6, and R 90 S, this 187-page English-language PDF contains BMW Customer Service's factory workshop manual, organized by numbered repair groups and job codes. BMW states that the publication is for master mechanics and fitters whose practical and theoretical Service School training is supplemented by the manual; its overhaul, measurement, and setup sections therefore assume professional workshop experience and equipment.

• Boxer engine repair includes compression testing, engine removal and installation, cylinder boring and honing, cylinder-head and valve work, crankshaft and main-bearing service, piston and connecting-rod inspection, timing-chain renewal, valve adjustment, and oil-pump checks.
• Fuel and engine-electrical coverage distinguishes the model-specific Bing slide, Bing constant-depression, and Dell'Orto accelerator-pump carburetors, then covers mixture and idle balancing, fuel-level adjustment, Bosch ignition timing, alternator and regulator testing, starter overhaul, and fault isolation.
• Clutch, five-speed gearbox, and shaft-drive procedures cover clutch inspection and centering, gearbox removal, cover sealing, gear-train and selector service, shaft end-float shimming, kick-starter work, and driveshaft removal.
• Final drive, suspension, steering, brakes, and wheels include rear-drive teardown and gear setup, swingarm bearings, spring struts, telescopic-fork measurement and rebuilding, steering adjustment, drum and disc-brake service, brake bleeding, wheel lacing, static balancing, and bearing setup.
• Factory reference material provides component-specific torque tables, metric and inch dimensions, capacities, wear limits, bearing and shim selections, electrical test values, illustrated special-tool use, diagnostic charts, component views, and the chassis wiring diagram.

Engine, Carburetor, and Electrical Detail

Model-specific engine tables cover bore and displacement, color-coded bearing shells, crankshaft and connecting-rod clearances, piston and cylinder grades, ring data, valve timing, lubrication, and oil-pump inspection. The manual limits cylinder regrinding to two oversize stages. Its repair chapters address main-bearing bush replacement and crankshaft endplay selection, cylinder-head removal with the BMW thrust bridge, valve-seat and guide renewal, piston orientation and weight matching, and flywheel runout checks.

Carburetor information is configuration-specific: the R 60/6 uses inclined Bing slide carburetors, the R 75/6 and R 90/6 use Bing constant-depression units, and the R 90 S uses Dell'Orto PHM slide carburetors with accelerator pumps. Jetting and needle tables accompany fuel-level, cleaning, choke-chamber, idle-mixture, and off-idle synchronization procedures.

Bosch electrical coverage includes points and centrifugal-advance service, static-lamp and stroboscopic ignition checks, alternator/diode-carrier/regulator testing, rotor and stator checks, and in-place starter testing followed by dismantling, brush, commutator, field-coil, and armature work. Separate alternator and starter fault-finding charts link symptoms to likely causes and repair actions. Chassis electrical sections add battery and relay service, the combination instrument and its drive cables, headlamp alignment, and lamp and turn-signal work.

Drivetrain, Chassis, and Brake Repair

The five-speed chapter records internal ratios and shim-adjusted axial float for all three shafts. It then documents gearbox removal, output-flange and cover work, complete gear-train renewal, selector forks, selector bracket and discs, neutral switch, and kick starter. Rear-drive coverage includes model-specific final-drive ratios, matched crown-wheel and pinion replacement, pinion depth, tooth backlash, contact-pattern checking, crown-wheel lateral-play shimming, and swingarm alignment.

Chassis work includes fork-tube straightness and parallelism checks, damper disassembly, seal protection, steering-bearing adjustment, and hydraulic steering-damper service. Front-brake coverage separates the R 60/6 duplex drum arrangement from the hydraulic disc systems and the R 90 S twin-disc setup. Procedures cover pads, floating caliper, under-tank master cylinder, brake bleeding, and hand-brake adjustment. Wheel repair extends to spoke replacement, rim-to-hub positioning, runout, balancing, and tapered-roller bearing preload. The frame data identifies the double-loop chassis as unsuitable for sidecars.

Tools, Diagrams, and Workshop Scope

Illustrated tool callouts include the BMW No. 6000 stand with No. 6005/1 jig, No. 205 main-bearing arbor press, No. 529/1 clutch centering arbor, No. 548 fork straightedges, and No. 550 spring-strut compression tool. Particularly useful visuals include the compression-indicator graph, cylinder-head tightening-sequence diagram, alternator and starter fault charts, crown-wheel/pinion contact-pattern views, and the full wiring diagram with cable-color and connector key.

Timing-chain links can damage the camshaft-sprocket rivet studs during removal, while the flywheel fasteners and mating surfaces must remain dry. Gearbox notes identify selector-fork orientation and protection of the clutch pushrod felt ring and seal lips; mistakes here can cause jamming or seal damage.

This is the factory workshop repair publication, not the Rider's Handbook or Spare Parts Catalogue. The foreword refers users to separate Special Tool and Spare Parts catalogues; required tools are shown in the applicable jobs, but the complete tool and parts listings are outside this PDF. Support the motorcycle securely for engine, transmission, wheel, or suspension repair, disconnect the battery where directed, and keep hydraulic brake fluid away from painted surfaces.