Benelli 250 Bialbero
With Phil Aynsley
The bike you see here is the Benelli 250 Bialbero that Dario Ambrosini won the 250 cc World Championship on in 1950.
I photographed it in the Morbidelli Museum back in 2011 but it sold in 2020 for £138,000 at auction, setting a new record for the marque (which was raised to £149,500 minutes later for an ex-Provini 1964 250/4!).
Benelli’s 250 single was a follow on from their successful 175 cc racer and debuted in 1934. The bike deliberately retained most of the 175’s features in a, “If it ain’t broke, don’t fix it” approach.
The only notable change was the move to a long-stroke design. The double overhead camshafts were driven by a cascade of gears and a separate four-speed gearbox was used.
The oil tank was located behind the dry-sump motor. The 250 set a World Speed Record in its class in 1934 for the flying kilometre of 181.81 km/h but its GP career was not as successful as the Moto Guzzis that dominated the class.
By 1936 a revised 65 x 75 mm bore x stroke was employed and factory rider Ted Mellors won the 1939 IoM Lightweight TT. Suspension was a single spring girder fork and plunger rear.
A supercharged version was designed to go head to head with the blown Guzzis and DKWs but the war intervened before it could be built.
When competition resumed in 1948 the old 250 returned to the track in Ambrosini’s hands, resulting in the title two years later.
Output was 27 hp at 9500 rpm, weight 115 kg and top speed reached 180 km/h.
Benelli 250 Bialbero Specifications
| Benelli 250 Bialbero Specifications | |
| Engine | Single-cylinder, four-stroke, two-shaft overhead geared distribution |
| Displacement | 248.8 cc |
| Cooling | Air-cooled |
| Tranmission | Four-speed, separate |
| Power | 27 hp @ 9500 rpm |
| Max Speed | 112 mph / 180 km/h |
| Frame | Single cradle tubular frame, stamped plates |
| Suspension | Parallelogram front suspension, elastic hub suspension |
| Brakes | Side drum, front/rear |
