This is from the site Bring a Trailer (https://bringatrailer.com/) ...
This 1939 BMW R61 is finished in black and powered by a numbers-matching 597cc opposed-twin paired with a 4-speed gearbox. The bike was reportedly brought to the US by a service member and was stored for many years before being recommissioned by the current owner in 2012. It has reportedly been driven thousands of miles since completion of the work, including roundtrip from Oregon to Monterey, California. Modifications include an R5 front end, an R69 seat, and a stainless steel exhaust system. This R61 is now offered on dealership consignment with spare parts and a clean Oregon title in the current owner’s name.
The black paint shows its age, and close-up photos of the bodywork, fuel tank, and fenders are provided in the gallery. Hydraulic telescoping front forks from a BMW R5 have been installed.
Additional equipment includes a stainless steel exhaust system, a seat from a BMW R69, and a horn from a Pre-A Porsche 356. The front wheel rim was replaced by the current owner, and the brake shoes were relined. A spare rear wheel rim and the original front rim accompanies the sale, along with a pair of unpainted front and rear fenders, though the seller notes that the license plate is not included.
The speedometer gauge needle is broken, and the odometer currently indicates 13 miles, though total mileage is unknown. Several spare gauges, housings, and associated parts are included and pictured in the gallery below.
The 597cc opposed-twin is linked with a 4-speed gearbox. The top end of the engine has reportedly been rebuilt with new rings, valves, and custom guides. Additional maintenance performed under current ownership is said to have included overhauling the carburetors with new sleeves and slides as well as the installation of a cloth-covered wiring harness.
Engine stamping #604769 matches that on the chassis plate pictured in the gallery. A start-up video is presented below.