Mention was made in a previous story about finding and acquiring a fairly rare 1976 Benelli 750 Sei (Six in Italian), basically Honda DNA in an Italian wrapper
The bikes were announced in the early 1970s by De Tomaso however even with getting an engineering head start by using Honda’s basic CB500 Four as a template, the actual bikes didn’t arrive for sale until about 1974. Revisions to the 750s include a revised transmission/clutch and the early 38mm forks were pared down to 35mm units by the time that this machine was born.
The “back story” behind this bike is that it was sold originally at Brattin Motors, here in San Diego. Brattin Motors was the local BMW dealership for many years, located on El Cajon Blvd. The site is now occupied by Trophy Motorcycles, after Brattin was relocated to Kearny Mesa and re-titled San Diego BMW Motorcycles. Being a Honda guy, I seldom had need or interest to look into the Brattin showroom, however I do recall seeing a Hercules rotary engine motorcycle inside for sale, back in the 1980s.
The Benelli was sold new to a man who rode it sparingly, let it sit for long periods of time and finally sold it to his best friend, who has had it for over 30 years. Again, the bike, being more of a novelty than regular transportation, was ridden infrequently, stored in a dusty barn/garage in rural North San Diego County. The combination of accumulated dust sitting on the chrome, coupled with years of temperature changes and winter storm moisture etched pits into most of the chrome-plated parts. The exhaust pipes, turn signal stalks, rear grab rail and headlight rim seemed to have been most affected, whereas the front and rear fenders, handlebars and fork tubes came out almost unscathed. Fine powdered dust worked its way into every nook and cranny that was available and remained in place for the better part of the past 20 years, at least.
My general observations on vintage Italian motorcycles is that the chrome is often not of the highest quality and the rubber parts fail much earlier than most of the Japanese made parts I have seen in 50 years of riding/driving and fixing bikes and cars. In the case of the Benelli Sei, the 3:6 carburetor setup was affected by intake manifold insulators splitting open along the clamping seams. When the bike was first visited, it fired up, but needed choke applied all the time and a handful of throttle yielded some sharp backfiring and stumbling which prevented any kind of genuine test ride for evaluation. Still, the engine did run, did not smoke and didn’t make any alarming noises while it struggled to stay running.
The seller had a high asking price which was tempered by closer and closer inspection on areas which would require considerable expense and diligent searching in order to locate Sei-specific parts just to get the bike to just a drivable condition. While the tires had been replaced, it was done over 10 years ago, so the “new tires” were showing ozone cracking, despite few miles traveled. I mentioned a lower price, based upon future research into the bike’s actual market value and the cost of replacement parts. Having just gone through a tortuous month of reviving a 1971 SAAB Sonett sports car (another out of production model with little in the way of technical and parts support), I was wary of diving into the deep end of the financial commitment pool only to find that I would be spinning my wheels futilely, once again, on a machine that needed the expertise of a true restoration expert in the marque.
I sat on the whole deal for a couple of days, spending many hours researching the who/what/where/how of these bikes, including who to go to for guidance and where to find needed parts for the bike. I started with contacting the owners of Cosmopolitan Motors, who were “the source” for Italian bikes for many, many years. Unfortunately, they had a big auction and sold off all the Sei parts to a company in Germany. Many parts seem to be available on their site, but without pricing! Plus, despite Google’s best efforts to translate, the site is in German language, primarily, so that makes parts selection and communications a bit difficult.
I called the seller back after a few days and told him what I had discovered about the bike’s “value” in the estimation of the www.nada.com site and cost of parts to bring it back to full function, once again. I made an even lower offer and said that I thought it was a “good condition” price offer for a “fair condition” motorcycle. The next day he called back with news that he would accept my offer and I hurriedly made the half-hour drive once again to gather up the machine, spares and paperwork to secure my new “Honda Six” Benelli motorcycle! Even with the engine off-song, the sound of the 6:6 megaphone-styled mufflers is truly breathtaking, reminiscent of a few of the CBX machines that I have owned in the past. I was pumped to say the least, despite the known amounts of work needed to get the bike cleaned up, tuned up and registered once again. The nice “extra” feature of the bike is that it has an original personalized CA Blue-plate that says “SEI”. There was an underlying feeling that I was marrying Sophia Loren, but with a bad case of measles on our wedding day. Sometimes, you have to just look down the road at the best possible outcome and make your choice. One day, the measles will be gone and the innate beauty will return.
Once the bike was rolled off the truck, the real learning curve began. I removed the headlight assembly to help knock down the deeply rusted, rubber cushioned rim. The headlight shell was pushed off to one side by some kind of storage tip-over incident, which bent the headlight ears in the process. With some scrubbing, bending and hammering, the fork ears straightened out pretty well and that put the headlight shell back to center once again. The only matching headlight rim available at the moment was one listed on eBay for $300! I found a Moto-Guzzi site that had new rubber cushions (for the US spec sealed beam headlights), listed at $48. The old cushion was falling apart, so the choice was to buy a new one and work with the rest of the parts as much as possible. Benelli poached a number of lighting components from the Moto-Guzzi line, back then, so it helps to widen your search parameters beyond “Benelli Sei.”
The mufflers were much more rusted on the left side than the right side, due to however it was stored. The tail light lens was intact but completely faded from red to near-clear coloration. The rear grab rail and turn signal stalks were deeply rusted. There were US mandated plastic reflectors attached to the outer portion of the turn signal housings, but they had all fallen off years ago, replaced by some reflective tape glued into the recesses of the housing.
The top of the engine’s cylinder head covers were suffering from some scale on the aluminum castings and rust on the fasteners. With the fuel tank removed, the carburetors were easy to access and evaluate. The original air box was removed as some of the parts were damaged and the ignition coils had been playing up. The seller’s motorcycle buddy had taken time to fabricate a steel plate to anchor new dual-lead coils in place and then added pod filters to the carburetor inlets. The intake manifold stub insulators looked an awful like CB500 Four parts in my mind, but I didn’t have any spares to compare them with. When the insulators were removed and flexed in the middle, one of them exhibited a large crack which was an inch long, obviously sucking excess air and dirt through the fissure. The other two insulators were only slightly better in condition, but were not cracked all the way through like the first one. As a “band-aid” repair, I bought a foot of 1 1/4” rubber fuel hose from the local auto parts store and sawed off three pieces for insulator replacements. While it was certainly a help, running the engine revealed continued air leaks around the manifolds, so some new CB500 Four manifolds were ordered up from Marty Mattern, through his 4into1.com website, which specializes in vintage Honda parts for sale.
When the bike was fired up on the hose manifolds, I could hear that it wasn’t running cleanly on all cylinders. In fact, the #5 exhaust pipe was virtually cold vs. all the other 5 cylinders. Pulling the spark plug revealed dark black carbon deposits causing the plug to short out. I installed a spare used plug and the cylinder revived itself, but it was obvious that the engine needed a new set of spark plugs, a timing check and some testing of the original metal-jacketed spark plug caps attached to the new spark plug wires. Eventually, all the spark plugs were removed using the OEM special spark plug socket, then the compression was checked. All cylinders came up around 170-180+ psi, so the engine was still in sound condition from a mechanical standpoint. Testing the spark plug caps revealed one with 74k ohms, instead of 5k ohms and two came up with “infinite” readings on the meter! There were two spare long style NGK non-jacketed spark plug caps in the parts boxes and I dug out an old CB750 cap that was still in specs for testing.
The bike started quickly and took throttle a little better, but the air leaks were still present at the manifolds so I knew that I was on the right track. The 4into1 order arrived quickly and I was finally able to actually compare the OEM Benelli parts with OEM Honda items. The ID was a perfect match and both had locating retainer ribs in the same place. The only actual difference was that the Honda parts were about a half-inch longer. Once in place, I worried about the additional length either changing the geometry of the three angled manifold connections or causing interference with the pod filters being pushed closer to the coil mounting plate. With some lubrication and a good tug, the three manifold insulators snapped into place and I was still able to squeeze the pod filters into place successfully.
There was some other work required on the carburetors, beyond my initial cleaning, as the middle carburetor’s enrichener plunger wouldn’t close down when the choke lever was moved back to OFF position. A half-hour of fiddling finally brought the desired results and the chokes were all working properly as I went to fire the engine up once again. The bike started instantly with full choke on and revved up to a fast idle. I slowly backed off the choke as I revved the engine and could hear the difference that the new air-tight manifold insulators were making to help bring the metering under control again. As a last check of the intake side, the manifolds were removed and new o-rings installed. Quick handfuls of throttle were now rewarded with a wild, wailing sound exiting the muffler ends. I do try to limit this kind of “testing” in the shop as we live in a residential neighborhood that could do without extended periods of WHOOP, WHOOP, WHOOP sounds as the revs built a crescendo of sounds reminiscent of 1960s Honda GP sixes. This thing is just trouble waiting to happen, from the sound of it.
Another couple of days of work yielded more promising results and more concerns. On the plus side, a set of new Bridgestone Spitfire tires of the appropriate sizes were ordered online, while on discount. Getting the tires mounted required wheel removal and lots of cleaning of spokes and the rim surfaces to get them to an acceptable level of appearance. The wheels really need a set of stainless spokes and rim polishing, but the current goal is safe street use with cosmetic improvements lower on the list.
During some on-line research, there was mention of the use of the CB650 oil pan and pickup on a Benelli Sei, to increase oil capacity and lower operating temperatures. For a $50 investment, some suitable eBay parts were purchased and proved to be an exact mounting match on the bike. The Benelli manuals show only 3.16 qts of oil as the normal capacity, which is slightly less than what a normal CB500-550 engine carries (3.4 qt with filter). The stock Sei oil pan was drained and removed, then compared to the CB650 part. The pan was about an inch deeper and the oil pickup had dual o-rings which were lacking altogether on the Benelli part. The OEM pickup literally fell out into the oil pan when the pan was lowered off the engine block. There was NO sealing function between the pickup tube and the receiver hole in the bottom of the block on the Benelli design. The multi-finned Benelli oil filter housing held regular Honda-styled oil filters, which are also available as a FRAM automotive filter part at local auto parts dealers.
Installing the pan back onto the engine was difficult on the right side due to intrusion of the #4 exhaust pipe header running close to the pan edge. It became necessary to loosen the pipe to gain some access to the two side bolts. It was going well until one of the two muffler mounting studs snapped off as the nut was loosened. One remaining stud should hold it steady, but it was disappointing to have to lose one of them during removal.
Once the pan was installed completely and the oil filter renewed, an entire 4 qt jug of Honda GN4 oil was funneled into the filler opening. The oil level came up to the top dipstick line perfectly. Once the engine is fired, up the oil filter and housing will refill and take the level down right between the two marks on the dipstick. That is a 25% increase in the oil capacity for this engine and should do wonders in keeping it cooler and fully lubricated at all times. I’m glad to have taken a chance on doing this modification and have it come out just as planned. It is hard to imagine why Benelli engineers thought that 3 quarts were enough to keep the engine cool during hard running, but that’s what they did.
In the meantime…
The local Honda dealer installed the new BS tire set, replacing some ancient Metzlers. It took two trips to the local DMV to get the bike registered and the “Sei” license plate re-assigned to the bike. The personalized plates actually belong to the owner until they sign a release to have it transferred to a new owner. The first order of parts came in from Germany, which included a new set of footpeg rubbers and a NOS full driver’s tool kit in the blue vinyl bag! I am currently awaiting a replacement inner fender liner (plastic) which was necessary due to some extreme tire rubbing on the original part. The shocks were knocked down for cleaning and a little quick repainting of the top plastic covers. They still look kind of rough, so replacements might be on the order list, unless some upgraded 12” shocks can be found to fit.
It is interesting/frustrating to see how parts are designed and function in European motorcycles. The whole design concepts are radically different in execution while doing the same function as any other carburetor or electrical system. Use of metric fasteners of unusual sizes are scattered around the machine. The locknuts on the chain adjusters required a 7/16” box end wrench as the size was too small for a 12mm wrench and too large for a 10mm wrench. The front and rear axle nuts are a beefy 24mm size. Lots of nylon self-locking nuts are used throughout the bike, instead of the usual flat washer, lock washer combination seen on the older Japanese machines.
The instruments are housed in a plastic box with two halves, top and bottom. The bottom half is secured to the fork bridge by two bolts, housed in sleeves and rubber cushions. The plastic is quite thin and the original parts were cracked at the mounting points. Fortunately, my friends in Germany can supply the instrument box and lots of other small bits to help get the bike back together again and fully functional. The ugly, extended turnsignal stalks and housings were removed and small bullet K&S aftermarket turn signals have taken their place. I removed the rusty rear grab rail as well, to clean up the lines of the bike at the back. This bike is never going to be the original beauty that it once was, at least while I own it. Perhaps a future owner will take on the full restoration task, but I just want to ride the bike for awhile and enjoy the feel and sound of those six wonderful mufflers belting out motorcycle operatic arias.
The main order arrived from Germany a good two weeks after the order date. Tracking the package indicated that it sat at Frankfort for a couple of days before it came across the Atlantic. Then it seemed to have been held up in New Jersey for a few more days, then suddenly it was in Bell Gardens, CA. The trip down to San Diego took another day, but I guess that is the best they can do for “economy” postage costs.
A few surprises came out of the box of parts, wrapped up in German newspaper. The instrument housing mounting holes were several millimeters smaller than the original casing, so a multi-step drill bit was used to open them up to the correct diameter. The rear fender section, which was injection molded plastic from the factory showed up as a fiberglass reproduction, undrilled. There were faint outline marks in the mold for most of the holes, but the originals were oval-shaped stamped into the plastic. It is hard to drill an oval-shaped hole in fiberglass, so I just centered in the middle and drilled in for a place to start. Once a few bolts were started in one or two locations, the rest had to be opened up a little bit on the edges to allow for fastening the thicker panel to the frame.
I had installed some K&S little bullet turn signals and wired them into the system, however I failed to notice (or assumed) that the black wire was GROUND while the black with a white stripe wire would have been the hot lead for the bulb. WRONG! A fuse blew and then wires started heating up while I was troubleshooting the signal issues. I dismantled a turn signal and discovered the wire color problem so rewired all the signals for BLACK is HOT and grounded the Black w/white striped ones. While checking circuits, I discovered that the fuse block, which has 18 wires tied into it was showing some signs of overheating at some point in time, so the fuse holders were no longer holding the fuses tight in the ends. The fuse block is, of course, special to the bike, so either a new ones must be purchased or a wire around will be needed. There are actually only 5 fuses on the block, as the rest of the wires are meeting as junction points. I found a small fuse block at the auto parts store which could stand in for the needed fuses and perhaps allow the use of undamaged wire connectors as new contact points.
So, for the moment, we are electrically dead in the water, awaiting a solution to the wobbly fuse holder problem.