Engine: Overhead valve, flat-twin four-stroke
Bore & Stroke: 68mm x 68mm
Output(claimed): 18 hp at 4,000 rpm
Weight: 286 lbs.
Owner: Peter Nettesheim
A performance machine for the masses.
That was the target for BMW’s R47 in the late 1920s. And by learning from everything that went into building the previous-generation R37—a powerful but complicated and expensive machine—the German company’s engineers succeeded.
The key was keeping a close eye on manufacturing costs.
Starting with the 500cc overhead valve motor from the R37, engineers added a simpler frame and suspension, and stripped off unnecessary electronics. The end result was a bike that cost 36 percent less than the one before it, but still had sporting pretensions, thanks mainly to the motor.
The OHV boxer engine was similar to the side-valve version used in the R42 tourer, but it pumped out 50 percent more horsepower, making 18 hp and allowing a top speed of 70 mph.
It was what performance-minded riders wanted, and the company sold 1,720 R47s—10 times more than the R37—many of them to German club racers.
That’s because BMW didn’t just suggest the use of the R47 as a racebike, the company encouraged it. Indeed, street-legal electrical components—a generator, horn and lights—were an option. And the company offered a quick-release secondary fuel tank that could be used for longer races or detached for sprint contests.
But the R47 also saw competition at the highest level. A BMW factory team campaigned highly modified R47s, hopped-up with superchargers, beefier drivetrains and lighter frames.
The R47 also shares another distinction with other BMWs of its era. It was among the first truly modern motorcycles, featuring such forward-thinking elements as roller bearings in the valve rocker arms, replaceable bushings throughout and a modern control layout (with the exception of the hand shift).
The R47 was sold for two years, and served as the basis for the R57 that followed. The third-generation performance machine integrated a more powerful front brake and a more robust transmission into the R47’s proven design.