JENAL - A Potted History of Benelli Sei Range

There is a perpetual motorcycle myth that Benelli copied Honda’s engine design for their Quattro and Sei range so let us try and put this into some perspective. No modern day manufacturer in his right-mind would dare to blatantly copy another manufacturer’s product because the legal costs and negative publicity would be catastrophic especially someone with De Tomaso’s automotive experience and Hondas’ commercial might.

I would speculate that Benelli may had asked Honda to produce production designs to speed up product-to-market-place but don’t be mislead by this speculation, Benelli had a lot of their own engine internal design input. Although a relatively small company, Benelli were major engineering innovators and regularly copied by other manufacturers, including the Japanese.

For example, comparing a 500cc Honda piston and conrod with the Benelli equivalent reveals similar dimensions but better Benelli engineering by way of lighter components for reduced reciprocating mass. Similarly the Benelli inlet and exhaust valve shafts are waisted above their heads to improve gas flow in this area. Benelli chose to use only three Dellorto carburetors feeding 2 cylinders apiece in the interest of narrowing this area for improved rider leg room.

In 1978 Benelli launched the 900 Sei but still offered the 750 for a short while. Cylinder bore was increased and the stroke lengthened to 61 x 53.4mm equating to 905.9cc. Benelli’s excellent engineering produced 900cc pistons weighing the same as the 750. Power rose to 80bhp while top speed questionably peaked at 130mph. The 750’s twin front discs were retained and the rear drum brake became a disc, hydraulically linked to one of the front discs as per their now sister company Moto Guzzi.

Surprisingly the bike actually had a lower dry weight than the 750, possibly due to less exhaust system complexity. It had significantly different styling, with molded GRP body panels concealing the fuel-tank and a more conventional six into two exhaust system. A few were sold without a fairing, but it soon gained the small (period) round ‘Guzzi Le-Mans bikini style fairing, which was later replaced by a trendy square looking Moto Guzzi fairing.

Due to Benelli’s precarious financial situation, not all production models were identical and turned into parts-bin specials. Generally the 900 Sei Mk I’s were all red in colour, fairing-less in the beginning and eventually sprouting the round bikini style fairing. Detailed engineering improvements continued particularly with the launch of the Mk II’s. These were similarly coloured red but adorned with the later and squarer Moto-Guzzi fairing. Mk III’s were similar to the MK II but had a greater range of colour options.

The final version, the MK IV saw further minor upgrades and a styling trend of the period, towards an angular slash-style colour scheme, white over red and white over black. The old style insect-feelers style chrome mirrors were replaced with car style door mirrors, attached to the bikini fairing sides. It had an unusual instrument cluster and the exhaust system became (period, again) black-chrome. All in an attempt to up-date the model and save production costs while attempting to regain market appeal and improve sales volume to the ‘heady-heights’ of 1979-1980 where 522 & 322 machines were made respectively. Sei production ceased in 1988/89.