Postwar Rikuo Motorcycle History: Japan’s Harley-Based Flatheads

Postwar Rikuo motorcycle produced after Shinagawa survived World War II — Shinagawa survived World War II and returned to civilian motorcycle production with postwar Rikuo flatheads.

The wartime Type 97 program ended with Japan devastated but the Shinagawa factory still standing. That mattered because Shinagawa was back to producing civilian motorcycles by 1946.

Production levels were still low, with only slightly over 300 machines produced in 1947. Even at those low production levels, the number of Rikuos produced was nearly three times that of all the other Japanese motorcycle manufacturers combined.

Civilian Production Returns

Sankyo also produced a new engine in 1947, based on the 1935 750cc flathead engine that Harley-Davidson used in the RL. This was not an exact copy, as the Shinagawa factory no longer had access to blueprints from Harley-Davidson. It was most likely reverse engineered by the Japanese.

Postwar 750cc Rikuo flathead motorcycle derived from earlier Harley-Davidson RL patterns — Postwar Rikuo production centered on a 750cc flathead engine derived from the older Harley-Davidson RL pattern.

They also improved the transmission by adding a reverse gear for use on sidecar models. The same basic postwar arc continued: Rikuo kept building sidevalve flatheads, even as the motorcycles received practical updates for police, sidecar and utility use.

Police Use and Rikuo Improvements

The Rikuo remained popular during the postwar era and was the official vehicle of the Japanese police force. Production rose to roughly 2,000 motorcycles per year, and additional improvements were made, including a telescopic front fork and aluminum heads.

The new Rikuos were styled after the current models from Milwaukee, with the exception of the engine, which remained the 750cc flathead. That contrast is what makes the postwar machines so interesting: visually they moved with the times, but mechanically they still carried the old Harley-Davidson flathead ancestry forward.

Postwar Japan also saw American military motorcycles repaired, reused and rebuilt in other contexts, so Rikuo production sits alongside other postwar motorcycle work in Japan.

Showa Aircraft and the End of Production

The Shinagawa factory was bought in 1950 by Showa Aircraft, which was also building clones of BMW and BSA motorcycles. Production continued until 1959, when Rikuo finally went out of business, although an unknown number of motorcycles were assembled from spare parts until 1960.

Late postwar Rikuo motorcycle from the final years of Japanese Harley-based flathead production — Rikuo production continued through the 1950s before ending in 1959, with some motorcycles assembled from remaining parts into 1960.

By the time the final Rikuos were assembled, the company had carried the old Harley-Davidson flathead pattern through licensing, separation, wartime production and postwar civilian use. The result was not simply a copy, but a long Japanese branch of the Harley-Davidson story that started with imports and ended with a homegrown flathead motorcycle industry of its own.