The Yamaha RA31A 125cc V4 was one of the engineering marvels of the golden '60s Grand Prix era.
The tiny machines totally dominated the 1968 season following the withdrawal of Honda and their stunning five cylinder four strokes.
The rotary disc-valve
engine, mounted within a featherbed-style double-cradle frame, produced approximately 42 bhp at 17,000 rpm.
This
equates to 336bhp per litre - Formula
One car engines at the time were producing 135bhp per litre!
The RA31 was fitted with a 9-speed
transmission rather than their competitors' 12-speed setups.
This helped the
rider to keep the motor within its narrow power band and 9th gear
acted as an overdrive for longer downhill straights to maximise a terminal
speed of 140mph.
This print shows the RA31A stripped of its fairing revealing the intricate and complex V4 packed tightly into the frame.
Info panel contains technical data and stand out results