Founded in 1958, S&S Cycle is one of the most respected names in American V-twin performance. From their carburetors and iconic teardrop air cleaners to their exhausts, engine parts, and full drop-in motors, their stuff is everywhere. But their passion for the scene goes beyond just their manufacturing interests.
Last year, the company invited six American custom motorcycle builders to compete in the S&S Cycle Vintage Tour. Then they added a Japanese leg, commissioning three craftsmen from the Land of the Rising Sun to build S&S-powered bikes for the prestigious Yokohama Hot Rod Custom Show.
Masumi Tsuchino of Infinity Inc. was one of the builders who got the call. Given a choice of either a Knucklehead, Panhead, or Shovelhead engine from S&S Cycle, Tsuchino-san picked the Knuckle; an engine he had never worked with.
"I wanted to express my gratitude to S&S for giving me this opportunity by building a machine that would make them happy,” he tells us. "From the beginning, I had the desire to create a board tracker—which is our specialty. So the concept of this machine came from imagining, 'If S&S had existed in the 1920s, what kind of machine would they have built and raced?'”
Intent on taking this project to the next level, Masumi took the brand-new S&S Cycle KN93 engine that he'd been supplied and sent it straight to Tamamura Motors for an overhaul. The upgraded engine was matched to a six-speed Baker transmission and a pair of S&S Super B carbs. The crew also used the opportunity to polish the cases while everything was in pieces.
Masumi ordered a 1936 Knucklehead replica frame from V-Twin Manufacturing to host the fresh engine, but his vision for the project called for several tweaks. “Of all the genuine big twin frames, the Knuckle is the most compact,” he explains. “So I wanted to create the most compact bike that we'd ever built.”
“By using a girder fork with a 28-degree neck angle, we were able to shrink the gap between the front tire and the frame, and push the wheelbase to its limit. I also tried to use parts from various manufacturers that hadn't been used before—so I found and rebuilt the front forks from a British 1940s Ambassador 250.”
For the wheels, Masumi matched 28” front and 26” rear replica board track rims to a pair of drum brake hubs. The front uses a replica of a Ceriani twin drum brake hub, while the rear rim is laced to a classic Harley-style rear sprocket brake unit. The front forks were so narrow, though, that Masumi had to remove some material from the front hub to make it fit.
He also had the brakes refurbished by S Proud—a shop that specializes in "ultra-reconditioning" drum brakes. “By replacing the linings with Japanese-made ones and reassembling them, the brakes, while old-fashioned, still work well,” he tells us.
With the wheels in place and wrapped in vintage treads, Masumi saw more room for improvement. The rear tire was much narrower than the space between the rear rails, so he rebuilt the right-hand side to run closer to the wheel. Because of the chain and sprocket, the left-hand side couldn't be narrowed, so the rear triangle is asymmetrical—a detail hidden by the Knucklehead's cleverly-placed mufflers.
The exhaust system also hides the bulk of the Baker transmission, while tipping its hat to vintage Harley race bikes. “The combination of plated pipes and black silencers was inspired by photographs from the 1920s,” says Masumi, “and the outlet design was inspired by vintage aftermarket Knucklehead mufflers.”
With everything coming together, Masumi turned his attention to the Knucklehead's bodywork. He fabricated an ultra-slim fuel tank that riffs on traditional split tank designs, and then embedded a tiny Motogadget speedo in the frame tube that runs down the middle. A handmade box sits under the seat, containing both the oil reservoir and the electronics tray.
A replica 1920s saddle and an abbreviated rear fender complete the setup. Handmade handlebars sit up top, fitted with modified Kuryakyn grips, while a triangular headlight from CT Newman shows the way.
Most builds of this ilk feature foot clutches and hand shifters—but keen eyes will notice a regular see-saw foot shifter flanking the 2-inch Belt Drives Ltd. primary. "I wanted a bike that was easy to operate and that I could ride without any worries,” says Masumi.
“In fact, in the 1930s and 1940s, a racing part was added that turned a foot clutch into a hand clutch. The design of see-saw pedals was inspired by that part."
New Classic Painting handled the paint job, with traditional sign painter Rio Studio adding tasteful details. Between the timeless hues and perfect proportions, Infinity's S&S Cycle Knucklehead is not only the slimmest machine the shop has ever produced, but it's also one of the most handsome board trackers to ever grace these pages.
Infinity Inc. | Facebook | Instagram | Images by, and with heartfelt gratitude to, Kazuo Matsumoto
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