Yamaha rotary valve prototypes

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Following the incredible succes of the Yamaha Grand Prix team and the World Championship of Phil Read in 1964 in the 250 cc class with the unbeatable RD56, Yamaha tossed around with the idea of making new fresh sportsbikes with a rotary valve induction system, similar to the G.P. bikes.

 

The 250 cc and 350 cc machines, which later materialized as the YDS5(E) and the YR1 and were introduced as normal piston port engines in February 1967, could have looked as follows: (you can "click" the pictures for larger format!)

The first "mock-up" looks pretty neat, but it is evident that it should be a (too) wide engine. And the details show that the YDS5 cycle was ready for production.

 


The second example has styling elements like the pointed fueltank that were used for the YR1 350 cc. This could be an early 350 cc mock-up as the chain is on the left hand side already and the tyres look also bigger than on the 250 cc model. But I am puzzled, the cylinderheads look more YM2 (305 cc).

 


And this is the first model for the full 350 cc bike, not very beautiful, to say the least. The engine is now clearly the YR1 with normal induction. This type of airfilter was kept for the YR1 but covered by the sidepanels.

The frontfork comes completely from the YDS3C Scrambler. it shows that the Engineers were "clobbering" things together just to see what looked best!

 

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