TWO OF THE SAME

The two-stroke twin engine that began life as the Yamaha YD1 in 1957 went on to a long and illustrious existence, culminating in the RD series before the completely redesigned LC (Liquid Cooled) models appeared. Perhaps the ultimate version of the original design was the YDS5E, also known (in America) as the Catalina Electra 250. Why Electra? Not for any relationship to the Greek Goddess of the storm clouds, but for the fact that this little twin possessed something that its quarter-litre two stroke revivals did not – an electric, push-button starter.

Jim Scaysbrook

In fact, the YDS5 is actually two models. The original (let’s call it the Mk.1 to avoid confusion) used the same basic engine layout as its forebears, including the racing TD1A and TD1B. The latter of these two racers had come under the serious scrutiny of US legend Don Vesco, who modified the barrels and pistons of his machine to incorporate what became known as “Boost ports” – channels cut into the lower cylinder walls to act as additional transfer ports that breathed to the crankcase through corresponding orifices in the pistons. Yamaha very soon became aware of this engineering breakthrough and adopted it for the ground-breaking TD1C racers, which quickly shrugged off most of the bugbears of the earlier models and became the machines to beat in the 250cc class.…

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Old Bike Australasia (Digital) - 1 Issue, Issue 118

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