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BENELLI 750 SEI Six cylinder very Italiana
1-. De Tomaso era: In October 1971 the Argentinian industrialist Alejandro De Tomaso, purchase Benelli by buying 85% of the companyīs shares. The remaining 15% went to Marco and Luigi Benelli, sons of the late Giuseppe. The remainder of the family were no longer involved, but still owned Benelli Armi, the gun-making and general engineering offshoot founded four years earlier at the old city of Urbino 20 miles from Pesaro. Prior to De Tomaso to put into production the full range of new models needed to mount a successful challenge for showroom sales. The make Benelli was asociated to racing bikes, were Renzo Pasolini and Kel Carruthes won some races for the company with 250 & 350 four cylinder machines. Benelli race against MV with Agostini, Honda with Jim Redman and Tom Phillis and Yamaha with Phil Read and Mike Duff, having some victory that remainded for the motorcycle history. De Tomaso selected the 750 Sei as the new flag in the export markets of the world. It was the new expression of the Italian effort to challenge the japanese motorcycles with similar technologie made in Italia. Is it today the same actitude with MV and the new Ducati V4?. A range of Quattro models and twin two strokes were designed to complete the new era.
2-. THE SUPER SIX: STAND-BY The Benelli six was launched as a prototype in 1972 and in the shops in md-1974. The 750 Sei was a typical Italian luxury engineering creation. From the land of Maserati, Lamborghini and Ferrari, a bike with an stright six engine was a logical, almost obvious product. The 750 Seiīs engine itīs essentially an extended Honda 500 Four, with two-piece connecting rods and plain bearing big-ends, its crankshaft supported with plain bearing. On the crankshaft centre, a pair of sprockets were fitted, one driving a large chain to the 5 speed gearbox and the other a timing chain to the single overhead camshaft. Lubrication was wet sump, in unit with the gearbox. Three 24 mm square slide DellīOrto carburettors were fitted instead a bank of six carbs, finding simplicity of adjustement, lighter weight and increased knee room. The ignition itīs with three sets of points and mechanichal advance. To keep engine width to a minimum, Piero Prampolini, the proyect leader, designed that the electric starter ant alternator were tucked up and in behind the crankcase proper. These original solution were adopted some years later by Honda in the CBX six cylinder. But if the motor was Japanese-inspired, the rest of the Sei was pure italian and the stylist did a sensational job. From the suspension (signed Marzzochi in the first model), excellent fully welded chassis made by the factory NV Nino Verlicchi, electrical switches by Tommaselli, seat by Giuliari, race twin front disc brakes by Brembo, including and especific master cylinder and masses of polished alloy and the masterpiece of the six silencers exhaust system made by Silentium. The best quality of the italian accesories for the best quality italian bike.
3-. ON THE ROAD: Performance from the 747,77 cc (56 x 50,60mm) engine wasnīt spectacular. Claimed power output was 71bhp at 8.500 rpm but no more than 60bhp can be founded on the rear wheel. The idea was not a very powerfull engine, that could cost a lot of money designing new parts with new machinerie and tools specific for this model, but to extract the best of an enlarged 500 Four. They used the same 500 design for the crank, cam timing, valves, head, conrods, pistons, gearbox etc. The result itīs a master piece of engineering, the Sei itīs smooth, uncannily smooth and vibration free. Touch the throttle and raw power comes out in precise, well mannered increments and with a very excyting exhaust note. Nothing sound like a Benelli 750 Sei with six pipes. There is the electric start motor an a kick pedal too, very practical when low battery. The seat itīs confortable and the riding position itīs logical and all controls are well placed too. Designed as a sport-machine in 1972, itīs a touristic bike over modern especs. The controls are eassy to use and the cluch lever and brake lever are a modern touch. The gearbox are very soft, if well regulated, and all speed go up and down effortless and the neutral itīs easy to locate. The power band start from 2.000 rpm. but itīs over 6.000 to 8.500 rpm. when the engine push hard. With a six into one, (Marving please!) free air filters (K&N of course!), rejeted carbs and electronic ignition (Newtronic sir) the engine can to be revd. to 10.000 rpm with a very exciting exhaust music. Anyway you can run in 5th at 2.000 rpm efforless and open throthle to the red line. Fantastic!!!!! The suspensions are the bad point in the ensembly, but itīs easily performed: KONI at he rear and new SAE 20 fork-oil in the front. Early model blew their gearboxes under hard aceleration but Benelli quickly beefed up the components and by 1975 it was sorted. The problem was an inadequated hardening process on the pinions and the lack of oil feed to the gearbox bearings. The engine really isnīt as solid as an equivalent Honda. Italy simply couldnīt build engines to the fine tolerances used by the Japanese and the metallurgical process were not as advanced. The wet sump lubrication and the engine oil capacity itīs the same used in the four cylinder engines, but the running temperature on the six engine itīs highther than the four. Running under hot weather, like in the spanish summer, we need to control the oil lever frequently to evitate problems of overheating that cause serious damages in the head, cam and rocker arms. Fitting an oil cooling system or fitting a deep oil sump from an Honda engine, resolve all these troubles. If you need more than the original power plant itīs offerenig there is a lot a new technology products (big bore forged piston, racing cams, head tricks, electronic ignition, new set of six carbs etc) that can increase the power to 90bhp and more, reving the engine to 12.000 rpm!!! My personal experience itīs to work on a 900 Sei engine, that has electronic ignition and a new long stroke crank with new crankcases that permet to fit forged piston for Honda Fours from 62 mm to 64,5 mm. A Ravasio cam with lobes timing 25-55š in the head completed with 2 mm bigger valves can be feeded with a Malossi bank of six 24 mm DellīOrto carbs. The result itīs very spectacular but very expensive too!!.
4-. RESTORATION: TRIKCS AND TIPS Only 3.200 Benelli-Motobi 750 Sei were build in the Italian factory, and 1.058 of them were sold in USA. In Spain were sold more or less 500 bikes, over the oficial registration of the spanish Benelli dealer. The question itīs: How many of them are still alive? And if we arrive to find one: Are original parts to rebuild them? The answer to the second question itīs YES. There are very few specialist in locating and reproducing cosmetic and mechanics parts for De Tomasoīs Benelli at a logical price, considering the rarity of the machine. Itīs a beautifull bike for riding but a very expensive toy for restoring. The first sugestion is to be in contact with the nearest Benelli Club ant they can give you a lot of usefull information: tecnical info, price of new and used parts, periodical Club meetings etc. If you want a bike to be used regulary, and you are not very strict with the originality of your bike, I suggest you some points to be considered: -. Change the original ignition by triple points for an electronic unit made by NEWTRONIC especific for this model. Itīs very easy to install and works great!. -. Change the original fuse-box for a modern one with four fuses. Then modify the conectors of the alternator wiring for a modern multi-conector item. This solution have been introduced in the latest four cylinder models and in the 900 Sei, so it could be considered as a factory option. -. Change the original batterie Bosch regulator for a modern Bosch electronic one. He has the same shape, fitting legs and conectors. The reference Bosch is: 0-192-062-007-850 -. Put a head bearing kit to eliminate the original steering balls system. Itīs not an easy job, because itīs needed to made a new pair of metallic houses for the bearing, but the result itīs OK. -. Donīt eliminate the original air-box and check for any cracks in the plastic components or any holed rubber. The carburation itīs VERY sensible at this point. All the plastic components, manifold and pipe rubber have been remanufactured so itīs very easy, at a reasonable price, to fit all these item in new. -. If you decide to fit K&N carbs filters, put the needle in the top position and a 130 main jet, depending of the exhaust fitted in the bike. Itīs not rare to need a 150 or 160 main jet. Balance the bank of carbs before to fit them in the head and the final adjustement will be very easy. -. Itīs posible to fit a set of six 22 mm DellīOrto carbs, manufactured by Malossi. The response of the engine is powerfull, mainly over 6.000 rpm. A problem itīs the hardening in the throttle twist-grip for the six carbs, no too sensible at low speed but dramatic when a full open throttle is needed . This set of six carbs itīs made with two bank of four carbs from a Benelli Quattro- LS or Sport or from Honda 500-550 Four, including the metallics and rubber pipes from the head. The set of six carbs itīs the best option for racing or café racer use and only runs with K&N filters. The intake sound at 9.000 rpm is mystichal and if mixed with an exhaust six-into-one note, then the music itīs celestial!. -. Eliminate the original intake rubber with pipe compensating connectors for a new blank ones, from Honda or similar. -. Change the original cam chain tensioner, even if he look in good condition, for a reinforced one. A Honda 500-550-650 item or Yamaha SR-XT250 can help you. -. If you need to strip the engine, it could be very important to change the main electric start bearing in the primary axle and the primary chain too. No more start problems and take out that horrible noise of the engine at iddle. - Chech the cluch basket for any clearence beetween the base and the silent blocks. -. Put new NGK angled plugs cutting previously some mm. of the original coil cable. Eliminate aftermarket metalic plugs or the original ones made in rubber. - Check for a good heart wire for the set of three coils. - For fitting an oil cooler, look for the original Yamaha XJ650 or FZR 600-750 system ones, that fit neatly, including the oil filter cover, specials bolts and oil pipes. As an alternative all the aftermarket systems designed for Honda Four( 750-500-550-650) can be fitted. - For increasing the engine oil capacity in 500 cc, we can fit the pan oil sump cover from a Honda CB650 (part nš: 11210-426-000) with his oil strainer (part. nš:15150-426-000) and the original gasket (part nš: 11398-323-000). It only can be fitted with the original six pipes exhaust, because the deep sump touch the six into ones collectors under the engine. (sorry!) - Itīs posible to adapt a tensioner for the primary chain designed por the Honda CB650 (part. nš; 23150-426-000) but then itīs needed a welding for the fixation of the bolt support on the bottom crankcase. The final result itīs superb with not noises into the engine by this primary chain.
TECHNICAL SPECS
Engine sohc in line 6
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