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Project YX023/064/065 = R3 & DS6

In the late sixties, Yamaha's 2-stroke rivals were offering high performance midweight road sports powered by race bred rotary valve engines. kawasaki claimed a maximum power output of 40,5 hp with the A7 350 model, and bridgestone boasted 40 hp with its export only 350GTR. Yamaha was also readying a rotary valve engine as the power unit for models that were to succeed the R2 and DS5, and started designing motorcycles around it. YX023 was the original code, which later changed to 064 for the 250 and 065 for the 350. Halfway through the development, Yamaha's engine men found fantastic new power in their Daytona race engine that incorporated five groove-like ports, and subsequently discarded the rotary valve project. The R3 and the DS6 were powered by Daytona proven piston-valve engines. Design process also unfolded an interesting change of course halfway. Initially the 250 and 350 were almost identical save for minor details, but they were given separate and individual styling touches. 1) R3 (Jan. '69). Essentially a refinement of the R2 which had been given a minor design touch-up in March of the previous year. Clever color scheme made the fuel tank even slimmer. Overall length 2040 mm, wheelbase 1310 mm, weight 170 kg. Aircooled 2-stroke 2-cylinder piston valve engine, 348 cc, max power 36 hp @ 7000 rom, 5-speed gearbox. Tire size front 3.00-18, rear 3.50-18. 2) DS6 (Jan. '69) A classic teardrop tank made this motorcycle look refreshingly new-sort of shock treatment for Mods. Overall length 1990 mm, wheelbase 1290 mm, weight 140 kg. Aircooled 2-stroke twin, 246 cc, max power 30 hp @ 7500 rpm, 5-speed gearbox. Tire size front 3.00-18, rear 3.25-18. Both the R3 and DS6 had "C" type street scrambler variations with upswept exhaust system. 3) Project 023 in February '67. This was an engineering prototype to try out the new rotary disc valve engine and frame. Styling was no more than the current DS5/M2. 4) Bird's eye view of the prototype showing carburettors on either side of the engine.

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91/24 yx023

92/25 064 ds6

93/26 daytona racer

94/27 image sketches

95/28 rx350

96/29 rx350pro

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The 4 drawings on top show some early proposals for the “YX023” rotary valve Yamaha. The subsequent 2 pictures on the second row are already a mock-uo of one of the proposals. Approved in Feb. ’67. The fuel tank was made so slim that a horizontal frame member could be seen underneath. The oblong taillamp was also quite interesting. 11) 12) Lower row, at this stage, the only difference between the 250 cc and 350 cc model was the shape of the air cleaner box. 13) Right row, top from 3. In September 1967 finally the change to the Daytona 5-port engine was made. 14) Next is project 064, the 250 cc model, also with a piston valve engine. 15) The last picture shows 065 mockup, the 350 cc model, also with the piston valve engine, which became the YR1.