Heron Heads
I thoroughly enjoyed OBA 55 but there is an issue I would like to comment on. The Moto Morini 3½ article mentioned that Cosworth used a Heron cylinder head in a Formula 1 engine; not true but the real story is more intriguing. Cosworth did produce a race-winning Formula 2 engine with a Heron head, called the SCA. However their chief designer’s frustration with gas flow issues inherent in the Heron head led him to design his new Formula 1 engine with a pent roof 4 valve head. The new Cosworth DFV was the most successful car racing engine ever built. The real twist to the story is that Phil Irving was so impressed with the simplicity and power of the Cosworth SCA engine that he incorporated a modified Heron head into the Repco Brabham 620 engine used by Jack Brabham to win the 1966 Formula 1 World Championship. Although the 620 engine was down on power compared to its rivals, it had a lot going for it; a beefy torque curve, good fuel consumption and light weight, and when fitted to the excellent Brabham BT19 chassis, was a race winner. However it was soon eclipsed when the Cosworth DFV emerged in 1967. Sam Heron was an inspired English engineer who spent most of his career working in America on air-cooled aero-engines. He invented the Sodium Cooled exhaust valve that was first used in the Wrights Whirlwind J5 that powered Lindbergh’s Trans-Atlantic flight. Regarding the story of the Zenith Gradua in the same issue, the theoretical advantages of a finitely variable gearing system are attractive, but the practical application usually falls short. The main problem with the Zenith Gradua system was the complicated and expensive way of moving the rear wheel, which when worn led to movement of the back wheel. A simpler more practical system was a fixed rear wheel allied to a jockey wheel belt tensioner (that could also act as a clutch) or a pivoting springloaded engine like a Raleigh Runabout. However the best arrangement at the time was the two speed, all chain drive arrangement on Scotts. Introduced in 1908, the foot-change gearbox with clutch and kick starter, was years ahead of the competition and good enough to win the 1912 and 1913 TT races, it continued until 1922. Stuart Francis Invercargill, NZ