In the ratification The world of bicycle craftsmen, Shiro Nakajima stands out. His bike often functional, and sometimes even practical: the kind of model that a factory can build visualizations.
Some are designed to win races and others to overtake dirt roads sometimes. And then there are the machines that distill the fun of motorcycling down to its simplest, most mechanical elements. Like this BMW R75 / 6almost fifty years old but perfectly capable of keeping up with modern traffic.
For the untrained, this R75 could be a restoration. But keen-eyed BMW fans will spot a large number of well-reviewed modifications.
“I built this according to the client’s request,” Shiro tells us. “It looks simple and classic. But with 1000cc, new transmission and fork from a Japanese bike, it can enjoy the mountain roads to the fullest.”
When leaving the factory in Berlin in 1973, this 6-wheel boxer had a capacity of 745cc and a modest capacity of 50 horsepower. But when it comes to Shiro’s workshop, a traditional wooden building on the island of Honshū, the engine is past its best. So Shiro dismantled it, down to the last nut and bolt.
He chiseled out the cylinders to increase power, installed new pistons, and remodeled the valves and their seats. The new large head bearings absorb the extra strength and all the seals and washers are new as well.
The headers are mostly stock, but refurbished and modified at the end to accept the new muffler. What is unusual is that these are chrome-plated brasses, which are only slightly heavier than steel.
Bronze silencers are known for their ‘musical’ quality – and are sold in the Japanese aftermarket for Harley-Davidson accessories. An internal silencer is drilled to regulate emissions.
The original Bing carburetor is gone, replaced by the Keihin FCR39s, which can take advantage of more power and help deliver quiet power.
That power is now sent to the driveshaft via an all-new powertrain, built from post-1982 BMW parts — from the flywheel to the clutch and transmission. (“Improved engine response and better gearshift induction.”)
The entire powertrain has been blown clean, from the transmission to the engine cover and cylinder head. Classic airhead engines have never been so beautiful.
However, the fuel tank had rusted, so Shiro sourced a larger regenerator with vintage crowns, and subtly modified it accordingly. The deep gloss finish (and iconic ridges) was done by local expert Stupid Crown.
The tank sits on the top rail of a modified frame, featuring new rear washers, a seat and a shock mount. The pipe has been meticulously finished and cleaned, and coated with a thick layer of black powder.
Shiro sculpted the shape of the chair himself using urethane foam; It’s just long enough to hold a billion passengers, but looks more like a factory custom seat than a custom 21st-century design.
Two leather seats were later fabricated and upholstered by Razzle Dazzle. Customers can change them up to suit their taste: one has a soft gray hounda leather upper panel, while the other is finished in vintage Porsche houndstooth fabric – a favorite. customer preferences.
As far as possible. But one area where the vintage style needs a little help is in the suspension, so Shiro paired 41mm Showa forks from a much more modern Japanese sportbike.
They are hidden inside new, and are connected by three Hondas and a custom-built steering body. The front brake system uses a 300mm disc from Yamaha, plus 4-cylinder brake calipers and a radial master cylinder from Brembo.
The front end doesn’t look too out of place, helped by old-school rubber forks — and neither does the back end, suspended by old-school Öhlins shocks.
The wheels are new Excel rims connected to the restored hubs. This means that some spacers must be machined, for the correct fit and alignment, but it is well worth the effort. This rubber is Dunlop’s K81/TT100 compound, a modern reinterpretation of the OE fitting popular on many 1970s bikes.
The wheel from the tire is offset by a pair of aluminum fenders. Shiro used regular, universal fitting fenders, modified in shape and size, as well as hand-made struts and brackets to fit them seamlessly into the fork feet and shaft cap.
He also made many smaller, less visible parts like the brake pedal and the battery holder [above]which is itself works of art.
However, the rules are simple in the cockpit that sports classic aftermarket bars fitted with Tommaselli grips and a combination of Honda and Kawasaki switches. Train watchers will note that the headlight housing and speedo are from a/5 and not/6 though: a customer style request.
To get the headlamp to fit, Shiro had to fabricate a new bracket. It is not built from metal, but is machined from a block of Duracon, an engineering thermoplastic.
All are connected to a brand new set of electrical wiring, along with Motogadget’s keyless ignition system. And to get rid of the electric grenades altogether, Shiro also refurbished the starter motor and generator.
Even so, he couldn’t find taillights or license plate frames that would match the building or comply with Japanese regulations. So he designed and fabricated these parts himself, along with a fog lights attached to the engine guard rails.
This is one of those delicately deceived customs that will still attract admiring glances ten or twenty years from now. And with solid engineering, it will probably still function smoothly.
Shiro’s skills extend into the digital realm as well: he’s created an enthralling video that showcases not only his next-level crafting and machining skills, but also equipment. and the workshop techniques he uses to achieve the results.
Next time you have a few minutes to yourself, turn off the rest of the world and enjoy.
