Royal Enfield unveils its first modern 650 twin motor

Royal Enfield returns to the parallel twin format as its flagship motor.

The new Royal Enfield parallel twin motor unveiled yesterday in Leicestershire, England is undoubtedly a landmark. For Royal Enfield it could mark a return to glory after half a century of producing (sort-of-slow) single-cylinder motorcycles.

Almost 50 years ago, Royal Enfield, a pioneer maker of British motorcycles, closed up shop, ending production of the Interceptor and its mighty, 736cc parallel twin. The Interceptor and its motor had been among the biggest, hairiest products of the last days of the British motorcycle industry. Royal Enfield of India carried on building the single-cylinder Bullet, beloved in India, but, at 350 or 500cc, limited in power.

The new 650 leans forward, as if into the wind.
It's a bit of what used to be called "a sloper."

The new motor is 648cc but will be called a 650, as the 736cc Interceptor of old was always called a 750. It's an air-cooled motor, with twin exhaust pipes, like the original, but has an overhead cam instead of push rods. It produces 47 bhp, about what the original would have done.

Royal Enfield boss Siddhartha Lal has been quoted to the effect that the new motor, originally 600cc, was increased in size to make certain it could push a motorcycle past 100 mph.

An overhead camshaft brings Royal Enfield into the 21st Century.

The press release gives credit for the new motor to Royal Enfield's UK Technology Centre and Chennai, India teams. Royal Enfield, now based in India, is obviously proud. The press release calls the motor "beautifully clean and essentially pure, like the experience it provides."

"A highly refined engine, with true highway capability, the 650 twin engine has been developed to excel across a wide range of real-world conditions. Classically styled, the engine has been designed to achieve a high level of modern refinement. The twin pipes and the cooling fins on the classic air-cooled engine render a visually beautiful impact...

Even in the exploded view, the new 650 looks compact and tidy.

"The engine maintains an under-stressed 9.5:1 compression ratio and fuel injection system ensures that smooth, accessible power is available at all times."

Between the lines, "under stressed" sounds like a promise of reliability, something the Interceptor motor of the 1960s, like most products of its time, achieved only with careful care and attention to problem areas.

Talking about under stressed, consider that the new motor has a stroke of 71mm. The Interceptor of a half century ago had a stroke of 93mm! I would guess the shorter stroke will pay off in less piston travel and vibration.

Air cooled for simplicity, the new motor is also oil cooled;
as was the motor of the 1960s, in its final form.

To my technically unsophisticated eye, the new motor appears tidy and compact, while the sprawling motor of 1970 looked awesome. You couldn't take your eyes off the naked original. The new motor looks as though it wants to do its work tucked inside bodywork.

The beauty of the big original Interceptor motor was so striking
that a period ad didn't bother showing much of the rest of the bike!

Most riders will look for its true beauty in its performance. It is, as the press release headline states, Royal Enfield's "first modern 650 twin engine."

The testing ground of the real world awaits.

Chart compares the 750 Interceptor of 1968 with the new Royal Enfield 650.