This is from the site Bring a Trailer (https://bringatrailer.com/) ...
This 1975 BMW R90/6 is said to have been modified in 2013 by the head of Marketing and Dealer Development for BMW of North America in San Francisco, and was acquired by the seller three years ago. The bike was built as a tribute to the BMW scramblers that competed in the International Six Day Trial in the 1970s. Power is from a numbers-matching, air-cooled 898cc opposed twin that features a rebuilt top end, replacement Mikuni carburetors, and a custom-built exhaust system and is paired with a five-speed transmission with a replacement clutch. The stock fuel tank was stripped and clear-coated, and aluminum motocross fenders were mounted to a modified frame powder-coated in silver and black. Additional features include a replacement solo seat, Pro Taper handlebars, an Acewell digital speedometer, and more. Fluid changes for the engine, transmission, driveshaft, and final drive were performed in January 2020. This R90/6 is offered at no reserve with factory tools, three keys, and a clean South Carolina title in the seller’s name.
The stock fuel tank was stripped and clear-coated before being fitted with replacement knee pads and BMW badges. The seller notes dents and corrosion under the clear coat. The frame was trimmed of unnecessary tabs and powder-coated in silver and black. Modified period-style aluminum motocross fenders were fitted, as were a replacement taillight and turn signals.
Factory wire-spoke wheels were vapor-honed and polished. The seller will install new tires of the buyer’s choosing to replace the older Continental TKC 80 dual-sport rubber currently mounted. Suspension consists of an overhauled conventional fork with a replacement alloy top triple clamp and dual shocks on the swingarm. Braking is from a single disc up front and a drum in the rear, with the caliper and master cylinder said to have been overhauled and the pads and shoes replaced.
The rear subframe was shortened to fit the replacement solo seat, which is said to be from an older BMW police motorcycle. A leather roll was fitted to the rear fender and contains factory tools. Passenger footrests were removed, while the rider’s pegs were replaced with vintage motocross versions.
ProTaper ATV-style bars feature a crossover brace and factory switches. An Acewell digital speedometer with a 12k-rpm tachometer was fitted along with a Boyer Bransden electronic ignition setup and a replacement wiring harness. Approximately 2k miles are shown on the digital odometer, 1k of which have been ridden by the seller. The previous odometer is said to have shown 35k miles prior to the refurbishment.
The air-cooled 898cc opposed twin was rebuilt at Max BMW in 2013 using new cylinder bores, pistons, rings, and seals. The heads were glass-beaded, valve clearance was set, and the replacement Mikuni carbs were jetted and tuned. Engine, gear, driveshaft, and final drive oils were changed by the seller in January 2020.
Engine number 4962557 matches the frame stamp shown in the gallery below. The seller notes that the head tube badge was misplaced during powder coating.
The custom scrambler-style exhaust system features period-style mufflers. Power is sent to the rear wheel through a five-speed transmission which is said to have been fitted with a new clutch and seals under previous ownership. Cold-start and riding videos can be viewed below.