Engine: Single cylinder four-stroke OHV
Bore & stroke: 72 x 61 mm
Engine Capacity: 246cc
Maximum power: 46 hp @ 10,500 rpm
Valves per cylinder: 2
Ignition: Bobine, mechanically timed
Carburettor: Dell'Orto carburettors ø 30 mm
Cooling system: Air cooled
Lubrication: Wet sump forced circulation with mechanical gear pump
Transmission: Gear primary, chain final
Clutch: Cable operated with multiple wet disc in oil bath
Gearbox: 6-speed foot-change, bolted to the engine
Throttle: Cable operated
Frame type: Open cradle tubular and pressed steel
Front Suspension: Telescopic
Rear Suspension: Mono shock, Swingarm
Front Brake: Drum
Rear Brake: Drum
Front tyre: 18 in.
Rear tyre: 18 in.
Seat: Duck tail race seat
Top speed: 225 km/h (139.80 mph)
Weight: 112 kg
Aermacchi racing motorcycles were christened Ala d'Oro (Golden Wing). Alberto Pagani's 9th place at the 250's Dutch TT debut in 1960 demonstrated the machines's potential, which was confirmed the following week when Pagani finished 5th at the Belgian Grand Prix.
The need for more power led to short-stroke engine dimensions (of 72 mm x 61 mm) being adopted on the 250 for 1964, by which time a 350cc version had appeared. With increased power came increasing unreliability, necessitating a re-design for 1966 when larger flywheels, modified piston and connecting rod, dry clutch and wider gears were among improvements introduced. The works concentrated on developing its new two-stroke twin from the late 1960s onwards, but before then had introduced a bob-weight crankshaft, external flywheel and new crankcases with an extra main bearing on its four-stroke single. Although, the pushrod Aermacchi never won a World Championship race, it did achieve a number of second places, Alan Barnett's in the 1970 Junior TT being one of the most memorable.
Despite a lack of ultimate success in Grand Prix, the Aermacchi single was outstandingly successful at the national level and today, having benefited from another three decades of development, remains a competitive force in historic motorcycle racing.
Provenance: The original owner of the 1961 model pictured is Eric Cheers, a collector and famous TT racer of Aermacchi motorcycles. After his retirement from racing, he sold his entire collection. This 1961 Aermacchi 250cc Ala d'Oro racer was completely restored in the late 1980s, but remained unused in storage until 2006. It had had been standing with castor-based oil in it, so during restoration a complete rebuild of the engine and gearbox was necessary. This was carried out in August 2006 by Pete Causer of PDC Racing Ltd.