1968 Royal Enfield Interceptor
(Page 3 of 4)
May/June 2008
Photos and Story By Robert Smith
The Meteor and Super Meteor twins were smooth and reliable, though a lack of crankcase rigidity caused problems in the fast but fragile Constellation. Fitted with Amal’s all-or-nothing 10TT9 racing carburetor and aggressive camshafts, the “Connie” was quick, but crankcase distortion and poor breathing led to oil leaks, and an unreliable oil feed caused many blow-ups.
RELATED CONTENT
A motorcycle trip through Texas on British singles....
Motorcycles finally break into the most prestigious classic car show in North America....
News and notes from Motorcycle Classics...
View from the Sidecar – News, Events and Sidebars from Motorcycle Classics Time machine November/De...
Our long-term Royal Enfiled Bullet receives a host of performance and appearance upgrades....
Part of the problem lay in Wilson-Jones’ decision to use separate cylinder barrels rather than having both cylinders cast as one block, as BSA, Triumph and Norton did. Unfortunately, without the iron “block” to stabilize them, the crankcases twisted under load, allowing oil to leak. This was made worse by having the oil reservoir cast into the engine! The Constellation engine also suffered from crankcase pressurization because of inadequate breathing, forcing more oil out. It was perhaps the Constellation that earned Enfield the nickname “Oilfield.”
The Interceptor
When Norton introduced the 750cc Atlas in 1962, Wilson-Jones stretched the Enfield twin’s dimensions to 71mm x 93mm for 736cc. Now called the Interceptor, the new bike looked just like the previous year’s Constellation, except the cylinder barrels were symmetrical and interchangeable from side to side. Internally there was a new clutch, and cross rings (basically triangle-shaped metal O-rings) replaced the always-suspect head gaskets. And bolted to the back of the transmission was an extra engine mount to stop the crankcase flexing. It helped.
A U.S.-spec model introduced around 1965 featured separate tach and speedometer, a two-gallon gas tank, 12-volt electrics, a longer swingarm, twin headers and a seven-inch front brake. The home market model retained the Connie’s six-volt electrics, “siamesed” headers, five-gallon tank and twin six-inch front brakes. Neither brake option was very effective. But with 52hp and weighing only 420 pounds, the Interceptor recorded a fastest for the day “out-of-the-box” standing quarter-mile time — below 13 seconds at over 100mph.
Longtime Enfield chairman Frank Walker-Smith died in 1962, leading to the sale of the company and closure of the Redditch factory. And that should have been the end of the story, except that an independent subsidiary, Enfield Precision Engineers, was still in business, working out of underground caves near Bradford-on-Avon, Wiltshire. Established during WWII as a “skunk works,” EPE became engineering contractors after hostilities ceased. The new Royal Enfield brand owners, Manganese-Bronze Ltd., contracted EPE to continue building Interceptors.
Late in 1967, EPE launched a revised Mk1A Interceptor, the type Jim Stothard owns. Styled as a street scrambler, the “TT” Interceptor had coil ignition, twin Amal Concentrics, upswept exhaust and front brake “cooling discs.” Otherwise, it was mechanically identical to its predecessor, still with suspect engine oiling, single-acting front forks (they had no rebound damping) and the weedy seven-inch front brake.