Interceptor

It’s time to unmask one of the underrated gems of the British parallel twin genre

Royal heroes Triumph Enfield’s of and the British BSA Interceptor twins motorcycle have is one garnered industry. of the most unsung While of the attention, those in the know appreciate the virtues and qualities of the last of Royal Enfield’s post-war twins. The powerful and torquey 736cc parallel twin was the largest-capacity British bike available on the home market when it was launched in its 1962 MKI guise. If bigger really was better, this had to be the best Enfield yet. used In fact, by Royal the Interceptor Enfield for name a couple had already of years been – though only in America. There, it had been applied to a tuned version of the 692cc Constellation, available in S Sport (road) and TT variants, but it was the arrival of the MKI in the UK that really started the Interceptor story. The engine featured a new, nodular iron crank with both bore and stroke increased to 71 x 93mm. The massive ball and roller main bearings and double-action oil pump used on the Constellation were retained, the pump lubricating the crank via a filtered feed, and the rockers through a separate feed that ran through a pressure relief valve before draining back down the pushrod tunnels to the cams and finally returning to the oil tank – which was cast integrally with the crankcases. Cylinder barrels and heads were new, and the diameter of the head/barrel studs was increased to 3/8in. Magneto ignition, the old faithful Albion fourspeed gearbox and a rolling chassis straight from the old Constellation maintained some continuity between old and new Enfield twins. There was certainly more power – a claimed 58bhp at 6700rpm – though actual performance figures obtained varied considerably. US magazine Cycle World managed an average of 119mph with a best one-way run of 120.5mph. But in the UK, The Motor Cycle could only get to 108mph – though perhaps a compression ratio that varied, seemingly at random, between 7.5:1 and 8.5:1 may go some way to explaining that. Despite that, all agreed that the Interceptor was the finest twin to have come out of Redditch – or Bradford-on-avon for the 1967-on MKIA models. The final MKII models, introduced in late 1968, are probably the best of the bunch and it was a sad day when production finally ended in July 1970. From 1969, American entrepreneur Floyd Clymer had been buying engines for his Indian-badged hybrids and, when he died, the Rickman brothers bought the remaining engines, installed them in their own frames and marketed them as Rickman Interceptors between 1970 and 1972. But it’s the Royal Enfield originals that are the most common – and affordable – today. If you get the chance to try one, grab it. You won’t be disappointed. We’ve asked Royal Enfield specialist Allan Hitchcock to outline the development of the various Interceptor models and variants over the next couple of pages.