It’s one of the great conundrums of post-Second World War British motorcycling, as well as a missed opportunity, that no major manufacturer ever produced a 250cc customer road racer.
Riders were spoilt for choice in the 350cc and 500cc classes, from the likes of Norton, AJS/Matchless and even BSA, with the OHV Gold Star the king of Clubmans competition. But while Continental companies like Moto Guzzi, MV Agusta, NSU, Adler and Mondial all produced well-engineered, competitive quarter-litre customer racers, British riders were restricted to running cut-down 350s, or they could create their own specials from the ground up, like Bob Geeson’s magnificent REG twin, on which John Surtees won the 1954 British 250cc title, winning 15 races out of 17 starts.
But there was a third alternative, though, which was to modify an existing series production OHV single to overhead-cam induction via a purpose-built cylinder head and valve train. The humble MOV Velocette was the most frequent basis for such a mod, not least in Australia, which in those days was very much a long distance extension of the British motorcycle market, whence several cammy versions of this popular ride-to-work model emanated.
Of these, the most successful was the Eldee Velocette built in South Australia in 1953 by Les Diener, a gifted engineer as well as a skilled rider, who won two 250cc Australian TT championships with his self-developed road racers.
Born in Adelaide in 1921, Diener had a tough early life after his father simply disappeared from home to escape rising debts, leaving Les at age 14 to leave school (as was permitted back then) to become the family breadwinner, supporting his mother and two younger sisters during the tail-end of the Depression era.
Diener first found work in a machine shop, progressing to become a valued employee in the toolroom of Kelvinator in Adelaide. This was a protected occupation, meaning his attempts
