With a production run of about 3,200 units 750s (2,000 more of the 900 versions) and the last one coming off the line in the late 1980s, the Benelli Sei series machines are scarce and so is the knowledge behind them. A web search can turn up literature and reprints of road tests and scattered parts for sale, but when you own one of them you really need to get to the “gurus” of the marque to find out what the pitfalls are and what to do to extend their lifespan. “Common knowledge” about the design is that a great deal of the engine configuration was copied from the early Honda CB500 Fours. Indeed, quite a number of engine parts are interchangeable between the two models. The current in-house machine has benefitted by installation of a CB650 (enlarged CB500-550) oil pan, which had added capacity and was a bolt-on modification.
There is a Benelli Motorcycle Forum, which is open to all years and models of the now-defunct maker, but most of the emphasis is on the last of the water-cooled triples, which were discontinued just a few years ago. There is a sub-section for the “Classic models” including the Sei sixes and the earlier smaller fours, which reach all the way down to a 250cc Four. Moto-Guzzi and Benelli were under the same umbrella back in the 1970s, so shared models and parts between the two makes. In several cases, some of the exterior lighting parts (tail light lens and headlight rims) are found on both models and in some cases even some Ducatis of that era. Ironically, the special US-spec headlights and rims for those three are stamped Aprilia. CEV supplied much of the lighting components and instruments were made by Veglia.
In scouring the internet seeking resources and “experts” few were found, except for a Benellimotoclub in Spain. Enrique Martinez is the apparent “MrBenelliSei” guru of these models, apparently having rebuilt or restored a large number of these bikes over the past decade. There were known issues with the transmissions, clutch and charging systems, but with Enrique’s feedback on this early 1976 model more and more “lessons” are being learned. He has recommended that the bikes be outfitted with Electrex-brand regulator/rectifiers, which were designed for the Bosch-equipped Moto-Guzzi models. The Benelli uses the same type of alternator, using an excited field and carbon brushes to make contact with the rotor. A RR45 unit was ordered from Electrex and delivered promptly from the UK. After a couple of hours of rewiring the system and replacing the marginal fuse block with an automotive type some difficulties were encountered. While the charging system seems to generate upwards of 14v, the ammeter is showing increasingly large discharges as the bike is operated. The ammeter wiring was not altered during the installation and it seems to be functioning properly; when the ignition switch is turned ON, the needle deflects to the negative direction of the gauge.
The installation instructions were somewhat sparse and only one “troubleshooting” procedure was listed on the one-page sheet. The charge system has a “sensor” wire that needs 120-150ma of current to be supplied through the ignition switch or optionally the “charge indicator light.” A 2w bulb was suggested as a replacement for the stock 3w bulb, although the wiring diagrams show 1.2w bulbs for the instrument cluster lights. There was an option to bypass the bulb with a piece of wire, but none of the suggestions yielded more than the minimum 120ma current draw. The charge light comes on dimly when the switch is turned ON and then goes out immediately when the engine starts up, but the issue with the ammeter remains a mystery. After a perfunctory initial response to my queries for assistance (“The ammeter is wired backwards”), my requests for assistance have gone unanswered. Their website offers many offerings including some self-energized racing ignition systems for many vintage bikes, but apparently the owner is also the “tech department” and seems to be too busy to assist this customer, anyway. So far, their customer service … isn’t.
Additionally, it was advised that the ignition system should be replaced with the German-made Sachse Digital Benelli Sei ignition system. This system is fully electronic with adjustable spark advance curves, so the original points condensers and mechanical spark advancer are all removed along with their inherent limitations. The 750 Sei has a rather uneven idle and the engine rpms flatten out about 7k rpms currently, where the redline is nearly 9k rpms. The factory ignition points are very crude and the condensers are mounted in recesses behind the point plate, directly into the very hot engine cases, so it is easy to see how just about anything would be an improvement. The cost factor on the ignition system is nearly $400 and delivery time is unknown at this moment. The company has made quite a few different designs which are compact and cleverly tucked into the engine’s basic designs. There is even a system for the 250-305 Honda twins!
Comments to Enrique about the 2nd gear jerking sensation yielded his response in that Benelli apparently didn’t heat treat the transmission gears properly, so by the time they get about 20-25k miles, they have worn out and taken other parts along for the ride to doom. Every marque seems to have at least one or two experts on a particular brand/model and I was pleased to have the support of Enrique in this case. The transmission mods are obviously a big deal as far as having to tear the engine out of the chassis and split the cases for inspection and repairs. Fortunately, when the oil pan was removed for the CB650 swap there were no signs of metal chunking off the transmission shafts/gears so far. The 2nd gear issue is unnerving when you aren’t ready for it and it obviously isn’t going to improve over time. The transcribed parts list for the clutch and transmission updates is lengthy and the costs are probably going to be on the high side. I wonder if there are Honda gears which would fit in their place, but those secrets have yet to be revealed…
I don’t know if there is a language barrier, but only a small percentage of my numerous messages to Enrique for tips and technical questions have been answered in the past few weeks. Unfortunately, there seems to be little more in the way of “experts” out there that deal with Benelli Sei’s quirks beyond what I have found to date. Sometimes, you just have to figure stuff out on your own and hope that any “learning moments” are not too expensive or damaging to man and machine. I guess that this is what the “Vintage Italian motorcycle” experience is all about. Once you move away from the Honda DNA of the machine, the rest becomes a foreign language, at least so far.
Bill “Bill-Benelli” Silver
Fantastic race bike version image from