The Sei
750 Sei
First revealed in 1972, the Benelli 750 Sei was the world's first 6 cylinder production bike, although it was not available for sale until 1974. As part of new owner de Tomaso's attempt to compete with the Japanese, Benelli had released the 500 Quattro, with an engine which closely resembed that of Honda's CB500. The 750 Sei added another two cyclinders to become the world's first six cylinder production bike when it was launched in 1972. Manufacturing issues meant that it wasn't available for sale until 1974.
Styling was similar to the Quattro, with a six into six exhaust system making it instantly recognisable. The inline six cylinder engine, with its three Dellorto carbs claimed 71 bhp and a top speed of 118mph, which was not particularly impressive. This, combined with the high cost of the bike, and the release of the Honda 6 soon afterwards meant that Benelli did not benefit as much as might have been expected from the release of the Sei, although the bikes are now highly desirable. Very early models suffer from crank and gearbox weakness, but this was soon fixed.
900 Sei
1978 saw the release of the 900 Sei. Cylinder bore was increased and the stroke lengthened, increasing capacity to 905.9cc, bhp to 80 and top speed to 130mph. The rear brake was now a disc, and the bike actually had a lower dry weight than the 750. It had significantly different styling, with moulded body panels concealing the tank and a more conventional six into two exhaust. A few were sold without a fairing, but it soon gained the small round Guzzi LeMans fairing, which was later replaced by the square fairing.
The final version, produced in small numbers from 1985 saw it move firmly into the 1980s with a black painted engine, black exhaust system, unusual instruments and new colour schemes, although other differences were minor.