Phil Aysnley looks at a 1964 Benelli 250/4 Racer
Benelli’s first 250/four was the 1939 water-cooled supercharged machine that was obsolete after the post-war ban on forced induction – Benelli 250/4 Supercharged (link).
Ing. Savelli designed a new 250/4 that was first raced in 1962 and which was developed, through about a dozen examples (none of which were the same), into Kel Carruthers’ 1969 title winning bike. The 250/4 campaigned in the early ‘70s by Saarinen and Villa was a completely different design by Savelli’s sucessor Piero Prampolini.
This particular bike is Provini’s 1964 Spanish GP winning machine sent to the US for display at the Daytona Motor Show by the US importer Cosmopolitan Motors. It stayed in the US until it was bought by the current owner and exported to Spain) and is quite different to the original bike that was raced by Grassetti during ’62-63.
The two valves per head were set at 90º (later to 63º and then to four valves per cylinder) and a seven speed gearbox was commonly used (although five to eight speeds could be fitted).
The prototype had a dry sump with the oil tank fitted under the seat but this soon was changed to a bolt-on sump that held two litres. Likewise the original battery and four coil ignition was replaced first by a Lucas magneto, then in late ’64 by one out of a four cylinder Mercury outboard engine that could better handle the high revs.
The ’62 prototype used four 20mm carburettors, also fitted to this bike, no doubt before it was sent to the US, but later versions used either 24mm (more power) or 22mm (more torque).
Power of the ’62 bike was only 36.5hp at 12,500rpm but by ’64 it was up to 45hp at 14,500rpm, then 50hp at 15,000rpm from ’66 onwards. The later 16-valve motor made some 55hp at 16,000rpm but with a narrow power-band. A more torquey 12-valve (twin inlet/single exhaust) was also experimented with.
The ’62 bike’s frame was replaced by a more modern chassis in ’64 – still using Oldani drum brakes. Benelli was the first factory GP team to use disc brakes in ’65. This bike has the smaller 7.5 litre ‘short circuit’ tank fitted – a 9 litre tank was used for GPs.
The diminutive size of the bike can be seen here!