The YD-1
Specifications

The YD1 was equipped with a 247 cc air cooled two-stroke mounted in a double-cradle frame.
Two different versions were produced, the YD-A and YD-B with stroke ratio specifications
of 54x54mm and 56x50mm respectively. The light weight of the bike made it very formidable
in terms of handling and acceleration compared to rival bikes of the era, such as the Honda RC71.
In 1957, the YD1 won 1st-3rd place at the 2nd All Japan Autobike Endurance Road Race
(Asama Highlands Race).

Overall length × width × height: 1,935mm × 705mm × 935mm Weight: 140kg Engine type: Air-cooled, 2-stroke, in-line 2-cylinder, 247cm³ Maximum power output: 10.8kW (14.7PS) / 6,000r/min Maximum torque: 18.6N?m (1.9kgf?m) / 4,000r/min
The concept behind the YD-1 that would lead the domestic 250cc class

Drawing on the example of the Adler MB250, the YD-1's engine was a 2-cylinder design. Building a 2-cylinder engine was a new challenge for Yamaha and when it went into the design stage no other Japanese maker had yet built a 2-stroke 2-cylinder engine. Although the Adler was used as a model, components like the clutch assembly and dynamo were given original Yamaha designs in order to create a more compact engine. In the end, the Yamaha engineers created a high-performance engine that was low in vibration and pumped out an impressive 14.5 horsepower.At the time of the YD-1's debut, the trend in Japanese 250cc models was toward a greater sense of weight and presence. But, with the appearance of the compact YD-1, with its sporty engine performance, that trend would be reversed. Looking back now, we realize that the effect of the YD-1 was tremendous in setting the Japanese motorcycle industry on a course that would define its future.