JENAL - Benelli ~ A Potted History of Benelli Sei Range

History of the Benelli Sei Range:  The 750 Sei (Sei is Italian for six) was first revealed to the public in 1972, the world's first 6 cylinder production bike.  The 747.7cc bike produced 71bhp with a bore & stroke of 56 x 50.6mm and became available for public purchase in 1974.  It was designed to assist Benelliís new owner to compete with Hondaís ever popular CB500.

This breath of fresh-air-design was wafted in by new owner Alejandro de Tomaso as he launched the 500 Quattro whose external engine castings had a remarkable similarity to the Honda but internally was different and recognised as superior.  De Tomaso decided he needed to lift still further Benelliís game and added a cylinder to each side of the 500 Quattro engine and made the 750 Sei; the worldís first 6 cylinder road-going bike.  Anoraks please note - Honda up until this time in its history had only built 6 cylinder race bikes, the RC165, RC66, 2RC164 & 3RC164 range but no-doubt used this race bike technology to launch their own CBX1000 roadie in the late 70ís.

Seiís styling was similar to the Quattro but 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 for a superbike of the period.

This fact, combined with the high price of the bike, and the later release of the Honda & Kawasaki 6ís meant that Benelli Sei sales (during its production period of 1974-1989) were relatively poor with an estimated world total of 5,000 bikes sold - 3,200 750ís and 1,800 900ís.

There is a perpetual motorcycle myth that Benelli copied Hondaís 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 manufacturerís product because the legal costs and negative publicity would be catastrophic especially someone with De Tomasoís automotive experience and Hondasí commercial might. 

I would speculate that Benelli may had asked Honda to produce production designs to speed up product-to-market-place but donít 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.  Benelliís excellent engineering produced 900cc pistons weighing the same as the 750.  Power rose to 80bhp while top speed questionably peaked at 130mph. The 750ís 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 ĎGuzzi Le-Mans bikini style fairing, which was later replaced by a trendy square looking Moto Guzzi fairing.
Due to Benelliís precarious financial situation, not all production models were identical and turned into parts-bin specials.  Generally the 900 Sei Mk Iís 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 IIís.  These were similarly coloured red but adorned with the later and squarer Moto-Guzzi fairing.  Mk IIIís 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 Ďheady-heightsí of 1979-1980 where 522 & 322 machines were made respectively.  Sei production ceased in 1988/89.

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