Engine: Single cylinder four-stroke OHV
Bore & stroke: 38 x 40 mm
Engine Capacity: 47.75cc
Compression ratio: 7.8:1
Maximum power: 1.9 h.p. @ 6,200 rpm
Valves per cylinder: 2
Carburettor: Dell'Orto
Cooling system: Air cooled
Lubrication: Wet sump forced circulation with mechanical gear pump
Transmission: Gear primary, chain final
Clutch: Cable operated with multiple wet disk
Gearbox: Manual 3-speed, gear shift
Starter: Kick-starter
Throttle: Cable operated
Frame type: Tubular and pressed steel
Front Suspension: Telescopic forks
Rear Suspension: Dual dampers and swingarm
Front Brake: Drum
Rear Brake: Drum
Front tyre: 2.00 x 2.4 in.
Rear tyre: 2.00 x 2.4 in.
Seat: Dual seat
Fuel consumption: 1 litre per 70 km
Top speed: 60 km/h
Towards the end of 1954, BM presented a simple and inexpensive 48cc engine, from which the following year it obtained three well-made mopeds named respectively Signora, Sport and Supersport. The four-stroke engine was built by Somaschini of Trescore Balneario, in the province of Bergamo. This company has long been active in the field of precision machining and had established an excellent reputation in the motorcycle sector for its gearbox components. It began to manufacture engines, and these were chosen for some of the Moto BM lightweights. The engine had a cast iron cylinder, pushrods and rocker arms, and forced lubrication with gear pump. The gearbox was three-speed, and it was available in versions with 1.8 to 2.4 horsepower.
The BM four-stroke mopeds remained in the catalogue for several years, but did not achieve great popularity in part due to their price, considerably higher than the two-stroke models from the same manufacturer.
Source: Hessink's NL
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