Royal Enfield Constellation Classic Superbike

There is nothing, Amencans are fond of saying, 'like cubes'. The US market for both two- and four-wheelers has always had an enduring love affair with cubic capacity for its own sake, a lust that Royal Enfield amongst British motorcycle manufacturers most attempted to satisfy. Like most other major British factories, Royal Enfield's post war programme was yet another tribute to Alfred Turner's 1937 Triumph Speed Twin design.

Royal Enfield saw, as BSA, AMC and Norton also concluded, that their flagship model had to be a four-stroke vertical twin. The layout was compact, relatively easy to manufacturer, fitted readily into a conventional motorcycle chassis and developed a particularly punchy brand of power. So a twin it had to be. But those produced in Redditch would be bigger, and bigger in America, at least was best. Enfield's first post-war vertical twin, the 500cc Meteor, was launched in 1948.

This set the pattern for later twins, using a one-piece iron crankshaft, separate heads and barrels, and dry-sump oiling but with the oil neatly held in a reservoir cast integrally with the crankcases. Along with the 350cc Bullet, the Meteor also featured swing-arm rear suspension whilst BSA, Norton and Triumph were still persevering with plunger rear ends. In the USA, Enfields were sold under the otherwise largely defunct Indian name. Feedback from the States soon prompted the development of a larger machine, and in 1953 the 692cc Meteor was the result (known as the Indian Trailblazer in the US).

From the Meteor was derived the Super Meteor, then in 1958 the Constellation - basically a sports version of its predecessor. 692cc was a good deal larger than any other vertical twin on the market.

Not surprisingly the Constellation, and its 736cc successor, the Interceptor, have always been associated with prodigious bottom-end and mid-range power. This is partly due to sheer capacity, partly to the Constellation's long-stroke (70 x 90mm) cylinder dimensions. Where Triumphs tended to do it on revs, the 'Conny' offered sheer punch.

Royal Enfield claimed 51 bhp at 6250rpm for the Constellation. At 4251b, weight was relatively modest, and acceleration brisk. In 1960 a Conny was independently timed at 112mph, faster than any other British big rwin other than a sports version of the Triumph Bonneville. The down side ought to have been vibration, to which any such twin is prone, and a big one even more.

Enfield substantially reduced this by dynamic balancing of their crankshafts during assembly  the only major manufacturer to do so. Despite this, Enfield big rwins were never so popular as rwins from Norton, BSA and Triumph. The engine was regarded as strong, but somewhat staid often being associated with pulling sidecars, for which it was eminently suited. The gearbox too made by Enfield's sister company, Albion  was heavy and slow. Worst of all, they gained a reputation for leaking oil  'Royal Oilfields'  and for leaky cylinder head joints. Enfield twins also suffered several high-profile breakdowns in major production races. And they simply lacked the cachet enjoyed by many of their rivals.

Constellation production continued until 1962 and the introduction of the 736cc Interceptor, another long-stroke engine with similar characteristics - and shortcomings. A substantially revised Mk2 Interceptor followed, but neither was conspicuously successful and the company sold its last bikes in 1968.

Ironically this collapse stranded a shipment of engines en route to Indian in the USA, which subsequently (see page 64) found homes in the Rickman Interceptor. The other Indian connection is that the Enfield name survives in Madras, where 350 and 500cc Bullets continue to be produced.