If you notice carefully, one can only connect the dots looking behind on to history but not into the future.  Similarly, Royal Enfield, who is back to developing an all-new overhead camshaft engines in their future models replacing their traditional pushrod engines, back in time dwindled into the overhead camshaft configuration in 1961.  Developed only as a prototype by then chief engineer, Reg Thomas, the idea of a lightweight motorcycle was conceived in 1961 and the first prototype was completed in 1962.  The very motorcycle you see in pictures here and only one of its kind right now in the world!  This one-of-a-kind classic is going up on sale at the Bonham’s Autumn Stafford Sale. 

While the engine head, even though now utilising a single overhead camshaft setup, was made to look similar to the then popular Royal Enfield Crusader’s engine but lower down the engine had a different form with aluminium castings stretched along the centreline and aping the design seen on the Aermacchi Chimera motorcycles.  Powered by a 173.5cc single cylinder engine, the OHC prototype was being developed by Royal Enfield to bring an affordable commuter option to the then-struggling European motorcycle industry as well as abide by Britain’s 200cc engine cap which entailed lesser insurance fees. 

A chain drove the single overhead camshaft via a pair of pinions located on the crankshaft’s right-hand end with the chain operating through a tunnel cast inside the cylinder barrel with an alloy head.  Packaged inside an all-new frame, the SOHC engine was mated to a five-speed gearbox supplied by Royal Enfield’s longtime supplier back then, Albion.  Other cycle parts and components were taken from other Royal Enfield models as this was a prototype and was still being tested.  In its initial tests on the road, the general feedback received was positive with the 173.5cc giving decent performance and the new chassis providing good handling and road manners.  Unfortunately, even before the 173cc OHC prototype could see shop floor, Royal Enfield subsequently shut down its entire operations in 1970. 

Interestingly, the OHC project was followed up by two more prototype models, a 75cc and a 98cc, as well as, wait for it – a step-thru during the mid-sixties.  Albeit, powering these prototypes were the Villiers’s 2-stroke single cylinder engines with a five-speed gearbox.  The step-thru though was powered by a Royal Enfield Ensign 75cc engine with a four-speed gearbox.  The project was developed to counter the competition faced by the company from growing Japanese brands with their lightweight, frugal and convenient machines that were taking the UK market by storm.