One-Year Wonder: The 1937 BMW R6

“I got bit by the prewar bug,” John says. “There’s just something about the prewar BMWs. There’s nothing extraneous about them, and while they’re very basic, there’s a purity in their design that’s irresistible to me.”

He sold the unfinished R60/2, and started searching for a prewar BMW. That’s when he found the 1937 BMW R6, a rare, one-year-only motorcycle, for sale online. “I don’t want to name the dealer,” John says. “It was sold as a restored and ready to ride motorcycle, but when I got it and started looking at it I realized it had just been thrown together and wasn’t really as represented. It turned out to be just a lousy repaint over many incorrect parts and poor mechanicals. I was disappointed, but I loved the bike — because it was something I really wanted and because of its rarity. I also didn’t think another one would come my way.”

Built from the BMW R5

Engineered by Max Friz and introduced in 1921, BMW’s flat twin engine was first used as a portable industrial powerplant, but soon found its way into motorcycle platforms including those built by Victoria and Helios. When BMW merged in 1922 with BFW — maker of the Helios motorcycle — the company gained a motorcycle production facility.

By 1923, Friz had taken his 486cc flat twin (purportedly based on a British-built Douglas powerplant) and placed it in a tubular steel frame with shaft final drive. Dubbed the R32, this motorcycle had its cylinders placed in the cooling airstream, or across the frame, a layout that became traditional for BMW. Other manufacturers of flat twins such as Douglas placed the cylinders in a fore and aft arrangement.

From that point on, BMW engineered faster and more impressive motorcycles. However, troubles with frame tubes cracking, especially when used as a sidecar tug, led to using a heavier pressed steel-type chassis on some models. Introduced in 1929 on the 750cc sidevalve R11 and overhead valve R16, the pressed steel frame BMWs proved popular with the German military, and lucrative army contracts helped carry the company through the early part of the 1930s.

Changes to the 750cc flat twin were few until 1935 with the introduction of the R12 and R17. The R12 again featured sidevalve arrangement, while the R17 had overhead valve actuation and was sold as a more sporting motorcycle. Both now had 4-speed transmissions as opposed to the R11 and R16’s 3-speed units, and both still featured rigid pressed steel frames and shaft final drives. Importantly, however, with the R12 and R17 BMW introduced the first modern, hydraulically damped front forks.

A year later, in 1936, BMW introduced one of the most technologically advanced motorcycles of the day, the R5. Drawing from the company’s racing successes with supercharged 500cc flat twins, the overhead valve flat twin R5 became BMW’s hottest sporting motorcycle, with an all-welded tubular steel frame fitted with the latest telescopic fork, but with a rigid rear. The R5’s frame was similar to the one used on the supercharged compressor motorcycles, and it was this frame BMW used for the 1937 R6.

The BMW R6 becomes the company’s first 600cc motorcycle

Marketed as a touring machine alongside the cracking R5, the R6 was BMW’s first 600cc motorcycle. Although it was a sidevalve, it bristled with all of the technology BMW first introduced on the R12 and R17 with the hydraulic fork, and, in the case of the R5, a foot-shift 4-speed.

Equipped with adjustable damping, the latest BMW fork was ahead of its time. A rider could adjust firmness or plushness by turning a lever atop each fork tube, but restorer/owner John says the control is “really more of a gimmick than anything else” and doesn’t really seem to make much difference.

The 600cc R6 engine is under-square, with a 70mm bore and 78mm stroke, and is capable of producing a respectable 18 horsepower at 4,500rpm. Carburetors fitted to the R6 were twin Amals made under license by Fischer. BMW produced only 1,850 R6s, and according to BMW historian Ian Falloon it only lasted one year “because the military still favored the pressed-steel frame R12 for sidecar use.”

John figures there are currently perhaps 50 R6s left in the world, with 10 of them located in the U.S. Although the German military might have favored the R12, and later the R75, it would appear many of the R6s were commandeered during World War II.

“Mine was sold to a dealer in Danzig, but I suspect it was confiscated by the German army,” John explains. “There are traces of stamps on some engine pieces that indicate it might have seen some service. The stamp looks like a little eagle symbol, and it’s on various components.”

Getting John’s R6 back into shape

One reason for John’s disappointment with his purchase was that when he took the timing cover off to inspect the timing gears, one had been badly damaged and welded back together, and wasn’t even round. At that point, John didn’t even attempt to start it, but simply took the machine down to the frame.

With the skeleton bared, John discovered his R6 had a definite twist in the frame and one of the lower frame tubes was rotten with rust. He researched chassis repair facilities and located The Frame Man in Sacramento, Calif., and sent the R6 frame there for repairs. Fitted with a later-style solo seat, the forged lug ears that hold the spring pivot mounts on the R6 frame were missing. A friend in Europe located a rusty and wrecked R6 frame, cut off the forged tabs and sent them to John, who had them welded to his freshly massaged chassis. For the period-correct seat, John found someone in Pennsylvania who was reproducing the metal frame; the rubber cover, like all of the other rubber bits and pieces, was relatively easy to source.

He disassembled the engine until only the crank was left in the crankcase, and then enlisted the help of BMW specialist Craig “Vech” Vechorik at Bench Mark Works in Sturgis, Miss. “I decided at that point that there were just too many unknowns, and while I’ve rebuilt Volkswagen Beetle engines, I didn’t want to jeopardize the prewar BMW,” John says, explaining his decision to send the entire drivetrain to Vech.

While some of the R6 engine components could still be sourced, a few of the pieces, such as the timing gears, could not. John found a spare R6 engine that yielded up the all-important gears, plus cylinders and heads that were in better shape than the ones he had. “On mine, one of the heads was cracked and the other showed evidence of having been involved with a blow up, and there were a lot of broken fins on the cylinders,” John says.

Because the wheels were badly bent, John ordered new rims and spokes to lace up to restored hubs, giving him the correct 19-inch hoops front and rear. The original brake shoes were sent to Bench Mark Works for relining, and John installed a ribbed 3.5 x 19-inch Avon Speedmaster tire up front and a 3.5 x 19-inch Metzeler Block C in back.

The tinware was in surprisingly reasonable shape. The fenders weren’t drilled full of extra holes and the gas tank was straight. The headlight ears needed attention as some of the metal was cracking, and they were “very wobbly.” An incorrect headlight bucket and bezel were replaced with ones John sourced in Germany when he went overseas to attend a motorcycle swap meet in Frankfurt.

None of the BMW’s components were powder-coated; anything that is black was sprayed by John Borella of Rhode Island. “John’s no longer painting, which is unfortunate because he did a beautiful job,” John Pavone laments.

“I’m more of an assembler, and I like to farm out the heavy work,” John says. But, with the machine coming back together, he did make his own wiring harness using cloth-covered wire and correct rubber covering, with a number of electrical pieces supplied by vintage electrical specialists Rhode Island Wiring Service Inc. In the interest of safety, John installed an LED taillight complete with a brake light switch.

John ordered mufflers directly from BMW, but the header pipes came from a dealer in Poland. They didn’t fit exactly as he’d hoped and required massaging before everything would line up. John finished the 1937 BMW R6 in 2005 and has since added perhaps 450 kilometers (less than 300 miles) to the bike. “I do ride it, but under the best conditions. There are a lot of challenging roads around here, with lots of potholes and lots of deer,” he says, adding, “It has plenty of power and torque, and it will get up to 70mph quickly, but the period drum brakes require planning your stops a bit early.” But that doesn’t matter. John has had a drink of the punch, and is definitely sold on BMWs. MC

The 1937 R6 isn’t the only vintage BMW John Pavone owns. Learn about the other flat twin-engined, prewar BMW in Another R: the BMW 1940 R12.