Yamaha YR3C

In 1967 Yamaha introduced a new model to their production line, known at the YR-1 Grand Prix. This motorcycle was the largest in the line that year, and represented a lot of firsts for Yamaha. It was the first 350cc motorcycle they had built. The engine was the first to use aluminum cylinders with cast iron sleeves, rather than all cast iron cylinders. It was the first to make use of horizontally split crank case, which made major engine work much easier.

The engine was a twin cylinder, piston port, two stroke, five speed, producing 36 horsepower, which at the time, was a big deal. The engine was a three port configuration, and the cylinder heads were machined to allow for squish of the compressed fuel mixture, allowing for a more complete burn. Another first was that the clutch was mounted on the transmission input shaft, rather than directly to the crank shaft. The advantages were that the input shaft rotates at much lower speed than the crank, there by making the clutch much more smooth in operation, and increasing the life of a clutch tenfold. It also had oil injection when many of its competition were still mixing gasoline with oil.
An innovative feature of the YR-1 engine was that the shift shaft and lever could be set up on either side of the engine. In Europe, motorcycles shifted on the right side, while in Japan and North America, the left. Likewise, the rear brake petal could also be changed to accommodate left or right side braking.

This motorcycle, to put it bluntly, was a road racing engine and chassis, with enough lights and instrumentation added, to make it street legal. When taken to the drag strip it absolutely smoked 650cc triumph's, and pretty much everything else.

It was produced in three colours, candy red, candy blue, and gloss black, being the rarest of the three. It was also given a lot of chrome such as both fenders, chain guard, handlebars, side panels of the fuel tank, gas cap, head light bezel, and so on. The front brakes were of the twin leading shoe variety, offering plenty of stopping power.
In short, this motorcycle was revolutionary in its day, and is a fairly rare classic today. The fact is, and it's no secret, that Yamaha borrowed the name of it's first road rocket for one of its newer machines, the yzf-r1.

This one machine set the stage for the future in the 350cc class. With never ending innovation taken from racing and applied to production, the YR-1 was the first in a long line of racebred motorcycles that followed. These were the YR-2 (1968), YR-3(1969), R-5(1970), R5-B(1971), R5_C(1972), RD-350 (1973-76), RD-400(1977-80), RD-350 LC(liquid cooled), and finally the RZ-350. The engine from the lc version lives today in the Yamaha Banshee ATV.

Source classicjapcycles.com