If V-twins are so wonderful, why is it that (mostly) inline fours rule the roost? This picture (courtesy A Herl Inc) is a 1928 OPRA 500 Quattro (four) that amounts to ground zero for every four cylinder motorcycle that followed. Although there were a few fours in motorcycling’s early days, those had a longitudinal layout that made for an overlong wheelbase and a tendency to overheat. The transverse layout was considered too wide and needing to be too high in the frame (for ground clearance in corners) to be viable.
But in 1923 Carlo Gianni and Piero Remor, who had met as engineering undergraduates in Rome, became convinced that the perfect racing engine might just be a transverse four, with all four exhausts facing forward towards cooling air. Four cylinders rather than the usual one, or two arranged as an longitudinal vee, meant a low reciprocating weight of everything from valves to pistons to conrods which allowed the engine to spin faster. Torque – the turning effort of an engine – is multiplied the faster an engine spins, so higher revolutions should give more power.
The pair hired a workshop in Rome and produced a 490cc 1924 prototype referred to as a GRB (Gianini, Remor, and sponsor [Count] Bonmartini). It was an inline four cylinder four stroke with a single overhead camshaft driven by a bevel shaft that rose centrally from the front of the crankcases. The cylinders were almost vertical, with a narrow valve angle necessitated by the single overhead cam layout. Claimed output was 28bhp at 6000rpm.
When Bonmartini was joined by Count Lancelotti in 1927 they formed a new company, OPRA (Officine di Precisione Romane Automobilistiche). What eventually appeared from OPRA in 1928 was to be pretty much the blueprint for the post war Gilera and MV fours (with better brakes than the ones in the picture) with a gear driven twin cam head. This was now making up to 34bhp, 20% more than the Rudge single that was probably the most powerful example of a single cylinder racing motorcycle at the time.
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