Gilera

The Gilera company was formed in 1909 by Giuseppe Gilera. The company was based in Arcore, in Lombardy, Northern Italy. As the pre-eminent Italian racing motorcycle before the War, it would be the obvious choice for 500 builders. Two engine types were considered:

The Saturno single-cylinder
This was developed just before the Second World War as a race engine. It was used in a small number of events before war intervened (and was the basis of the Italian military motorcycle), but war also ended earlier in Italy than the other major European nations meaning their automotive manufacturers had a head start on returning to full scale production. By 1946 the Saturno motorcycle was on sale to the general public, and stood head and shoulders above any other sports racer available (albeit with a price tag to match). With changes to Grand Prix rules coming into force for post-War racing, the Saturno engine proved eminently suitable whilst the Gilera 4 was redeveloped.

Around 1949-1950, Italian racers and constructors were considering the 500cc Formula that was about to become Formula III, and the Saturno engine was as obvious a first choice as the JAP engine was to the British competitors.

The engine was a classic upright in design, much like an AJS or BSA motor. In immediate post-War specification, claims were of about 36bhp @ 6,000rpm, competitive with a contemporary JAP on methanol. In motorcycle terms at least, the torquier single could compete with the peakier multi, and the racing version of the engine was certainly freely available to paying customers. For 1952 a dohc version was developed, giving 45bhp @ 8,000rpm, but this was abandoned as the Gilera 4 was now giving even better performance.

Like the JAP, the Saturno engine is a pushrod, ohv layout with aluminium hemispherical head, 84mm bore x 90mm stroke. A 35mm Dell’Orto carb was used as standard. Unlike its British counterparts, the 4-speed gearbox is integral, and the lubrication system is recirculating, wet sump.
 

Rondine 4-cylinder (aka Gilera Four)
This (normally used transversely) four was originally conceived in 1923 by Carlo Gianini and Piero Remor, but acquired by Gilera, via Piero Taruffi, in 1935. It would be continuously developed as the primary Gilera race engine right through to the 1970s. It was this engine that Taruffi used in his twin-boom Tarf-Gilera record car in 1948.

On paper, at least, the engine should be an ideal package for a formula III car:

Small cylinders enabling a much higher rpm, and consequently higher peak power (60bhp @ 10,500rpm was claimed)
Better balance of a straight four over the cylinder engines.
A double overhead cam design
Barrels canted over at about 20º off vertical, meaning a unit no taller than the choice of upright singles from Norton, JAP, etc.
Air cooled, avoiding the extraneous radiator and pipes of car-based engines.

Whilst engine width would require an original design for the rear of the chassis, and good ducting to cool the inner pair of cylinders, none of these seemed like insurmountable problems. The 1950-51 version seems to be a remarkably advanced design and would not embarrass in even a modern motorcycle. Four carburettors fed each cylinder individually.

The Rondine engine was never used for road bikes, so suitable corporate and political connections were necessary to secure units. But with Taruffi as Technical Director, this should not have been an issue (especially given the close relationship he developed with Charles and John Cooper in 1951).

Remor had quit Gilera in 1949, joining MV. When the first MV Agusta racer appeared in 1950, it bore more than a passing resemblance to the Gilera. Oddly, the MV never appears to have been considered as a Formula III power source.

The first to fit this engine was Enrico Nardi, though he mounted it quite high in the chassis, with shaft drive to the Fiat axle and a short wheelbase, handling would have been quite challenging.

The most obvious use of Gilera engines was in the Volpini – unsurprising as 1951 driver Nello Pagani was a Gilera works rider. Both engines were used, but success was somewhat limited. Although the cars were somewhat heavier than a contemporary Cooper, the main issue seems to have been the lack of fierce competition driving development at a comparable rate to the England. When the cars were sold on, François Antonelli managed to secure a Gilera 4 with his car.

Gilera four mounted in the Volpini

Quite why nobody every seems to have tried to fit this engine in a Cooper will probably remain a mystery......