I really have to stop throwing out internet bids on “interesting” bikes and forgetting that I did it until I receive notice that I have “won the auction”.
Those of you who have followed my ramblings over the past 10 years (or more) might recall that I acquired a somewhat troublesome Benelli Sei (750 six-cylinder) machine from a local seller who had had it since the 1970s. That bike was fun to ride and sounded amazing… when it would start. Even a $500 ignition system never insured that the engine would fire up easily. That, along with the factory defective transmission gearset (there was a recall that the bike never received) led me to let it go to a local Italian bike dealer who had the bike restored.
So, here we are again, with almost the same bike, but with fewer cylinders this time. The Benelli Quattro 500 is the Honda CB500 engine clone in virtually the same chassis as the Sei. The big departure is that instead of a double-disc Brembo front brake, it has a double-sided drum brake system with 4 brake shoes upfront.
The bike caught my eye on some Internet link to a big auction in Wisconsin in mid-Oct. It was open to internet bids a few weeks ahead of the actual date, so I thought I would test the waters to see how much interest there was in this rare machine. Benelli updated the models with the double-disc brake wheel later on, but few of these bikes were probably ever sold in the US in either form. I do recall seeing one for sale locally a number of years ago and visiting the seller’s place to see it in the flesh/metal. It, too, was a drum-brake model, but it wasn’t running and I shied away from it due to lack of parts and general knowledge of the series.
By the time I paid for this bike, plus a hefty 18% buyers fee and rounded up a U-ship guy to haul it out for $450, the initial bid cost had increased by 50% again. All that was shown in the auction page was both sides of the green bike and a short sentence about the frame number and perhaps the mileage on the odometer. The auction company did provide a WI title a few weeks after the bike arrived, which is helpful for getting a CA title for the bike, but you still have to jump through the DMV/CHP hoops to finalize the paperwork.
The main source for replacement parts is a company in Germany, which seemed to have gathered up all the remaining Benelli parts for all the models they could find. They have microfiche illustrations on-line and generally ship parts out quickly and at reasonable prices, all things considered. I did inquire about the H-shaped molded fuel hose connector in advance of receiving the bike and they did not have a replacement part for that item. There are four carburetors and two petcocks to connect all the plumbing together so I will have to round up T-fittings to get it all fueling properly.
The bike arrived within 10 days from the auction, riding tail-gunner on the back of a long, double-axle open trailer. At 20 feet, it doesn’t look TOO bad, but as you got closer the condition issues became more and more apparent. Fortunately, it did have some air in the tires and the 4 shoe front brake did function to a point. The friendly driver helped me push it up the driveway and into the awaiting bike lift for future repairs and a deeper inspection of all systems. It was one of those heart-stopping moments where you say to yourself, “What did I get myself into now?”
The first look revealed that there were NO spark plugs in the engine, no ignition switch key provided and the engine was LOCKED UP solid. The first thing to do was to squirt WD40 penetrating oil down each spark plug hole and hope that it would work some magic on the stuck pistons.
The design of the battery box is such that you cannot remove the backside of the air filter box to service the filter. Removal of various attached electrical components finally allowed the battery box removal. At that point, the bolt holding the filter cover turned out to be part of the inside of the housing, not accessible unless you remove the carburetors and airbox. The carburetors are connected with intake manifold rubbers which attach to intake manifolds which are bolted onto the backside of the cylinder head. The air filter box connects to the carburetors with short connectors, which unlike the outside angled versions on a CB500 Honda, are all straight-back designed parts. Pulling the connectors off the airbox and back off the carburetors allowed for carburetor removal. One of the carburetor tops was missing and the throttle cable had already been disconnected. SOMEONE had been in there before, probably trying to get it running sometime in the past 10-20 years.
On the plus side, the odometer only showed 1506 miles and the original Pirelli branded tires were showing little wear, which seemed to verify the miles shown on the speedometer. There was rust everywhere on chromed parts, other than the fenders, which were unaffected for some reason. There was surface rust inside the fuel tank, of course, but the carburetors were clean inside the bowls. The plastic meter box, which mounts to the upper fork bridge with a couple of bolts was broken at both attachment points. It was déjà vu all over again, as the basic architecture of the Quattro 500 is nearly identical to the 6-cylinder Sei. The Sei had double disc brakes up front, but both bikes shared the same rear hub and suspension. The Sei has alloy rims, where the cheaper 500 was left with chrome steel hoops, which were both rusted badly on this machine.
The fork ears had been chromed, along with the front brake hub stays from the factory. The brake stays were suffering from peeling chrome and the fork ears were in similar condition. The chromed headlight bucket was somewhat better, but the headlight rim chrome was badly pitted. The 4into 4 mufflers were solid, but with surface rust and pitting down in the creases. The header pipes were still in remarkably good condition, however.
Once the carburetors were removed, work commenced on getting the top end of the engine removed for damage assessment. Unlike Honda, Benelli engineers used #1 Phillips head screws to retain the top rocker arm cover. Fortunately, they mostly loosened with a few blows of the impact driver with a matching driver tip. More challenges were revealed when two of the Allen screws that hold the top cover end caps wouldn’t come out, stripping the hex heads of the 5mm screws. After trying various methods of removal, the heads were drilled off so the caps could be taken off. The end caps cover the last two end screws that hold the top cover to the cylinder head. The screws thread into the ends of the rocker arm shafts and there was no apparent reason for two to come off and two to be firmly entrenched in their positions. It took about a half-hour of careful drilling the screws out of the ends of the shafts, then rethreading the holes successfully. The cover then came off easily revealing shiny metal parts inside. The rocker arm pads were all like new and the camshaft lobes appeared to be barely broken in.
The camshaft is secured to the camsprocket with two bolts, but somehow the engine had stopped with both bolts lying right at horizontal positions. It’s tight quarters in there, so although the camshaft bolts could be accessed (remember the engine was frozen), you can’t back them all the way out of the camshaft sprocket as the heads hit the inside of the cylinder head opening. I tried to loosen the camsprocket bolts with an open-ended wrench, but they didn’t budge at all. I figured that the bolts had been installed with Lock-tite thread locker, so the only option was to try to loosen them with a large sharp chisel. The chisel was able to catch a corner of the bolts at just the right angle, but it took considerable amount of hammering to get them to begin to rotate loose from the camshaft bolt holes.
Eventually, both bolts were loosened successfully, but couldn’t be removed due to their proximity to the edges of the cylinder head. A Dremel tool with a cut-off wheel was used to cut half of the bolt head away just enough to allow the bolt to be removed from the forward bolt hole. The rear one remained in place, however. Using a long-handled adjustable wrench, I applied some torque on the crankshaft bolt, hoping that the engine would give just a little bit. Suddenly, the crankshaft turned about 10 degrees and the camshaft bolt was then clear of the cylinder head for removal. With the camchain free of the camshaft, the engine was turned back and forth a few times, finally allowing for full rotation of the crankshaft and full movement of the pistons.
The camchain tensioner bolts to the back of the head and cylinder with 2 bolts, but unlike Honda’s design, the mechanism can’t be locked in place for removal. When the bolts were removed, the tensioner spring wanted to push up against the back of the camchain, preventing removal of the camchain from the sprocket teeth. The tensioner was pulled upwards, but hit the frame backbone tube before it was clear of the cylinder head. Finally, it appeared that the tensioner could be compressed with my fingers and the whole unit rotated 90 degrees, which then allowed the top to be tipped over and just clear of the frame tube.
Once the camchain was off the camsprocket, the camshaft was removed and a wire attached to the camchain to prevent it from dropping too far into the engine. The cylinder head is attached with a series of flanged nuts and washers, some of which are sealed off by little rubber plugs in the head. With all the nuts removed, the head pulled up with a little nudging here and there. The valves had quite a bit of soft carbon on them, but showed little signs of use. The now-exposed piston crowns showed some signs of varnish, carbon and moisture corrosion. The cylinder bores had some pitting around the edges of where the pistons were sitting for so many years. The corrosion had eaten into the bores just enough to catch a fingernail on the edges, so the choice was to pull the cylinders for a re-bore.
A set of .50 aftermarket Honda CB500 pistons/rings were ordered up from Japan for $125 and the cylinders will go off to my favorite machine shop for $160 of machine work. Lots of scraping was involved to get the leftover gasket material off the engine cases, all the while trying to keep the loose bits from entering the open bores in the crankcase. The pistons all came off of the pins with little fuss, so there is no concern about damaged pin bores in the rods.
The a/m pistons came in from Japan in about a week. My machinist bored the cylinders and noted that one piston was a bit smaller than the other three, so bored the holes accordingly. After some wire-brushing to clean off excess corrosion, the cylinders got a bit of color added back. Benelli actually painted the cylinder blocks gold and the heads black from the factory! After an hour of careful prepping and assembly, the cylinders glided onto the pistons and the assembly awaited the completion of the cylinder head.
The cylinder head was disassembled and de-carboned. All the valve faces and seats looked great, but valve stem seals were hardened, so were replaced with gasket kit parts. In the process of reassembly one of the valve stem keepers dematerialized and could not be recovered despite an extensive search of the immediate area. I discovered that the valves were 5.5mm stems like the Honda valve stem sizes, but Honda keepers didn’t fit, so replacements have to come from Germany.
I was ordering parts from Benelli-Bauer anyway, as they are one of the last couple of resources for NOS Benelli parts. They can supply replacement instrument cases and most everything else that I have asked for so far.
In the meantime, I decided to go the poor man's route and have the rims powder-coated satin black, along with the formerly-chromed fork ears. Some new tires were ordered and after all the spokes were cleaned up, the finished rims were re-spoked back to the de-rusted hubs. There was extensive amounts of rust inside the drums, however, it did clean off with extensive use of wire wheels and abrasives. The brake shoes were glazed and had a thin film of corrosion embedded into the faces. A little light sanding brought back the original surfaces.
Rather than purchase all the Benelli gasket parts, one-by-one, I just ordered up a whole CB500 Four gasket kit and installed all of those parts without issue. Apart from the slightly-angled forward cylinders, much of the top end components are exact dimensions of Honda’s OEM CB500 designs.
The parts order from Germany took almost 2 weeks to arrive, so to speed up the assembly process an OEM Honda exhaust valve was ordered to match the keepers that were already purchased, but didn’t fit the groove pattern on the Benelli valve stem. Problem solved and the cylinder head was bolted down, torqued to specs. Two new camsprocket bolts were ordered to replace the butchered ones and the rest of the original parts reinstalled.
My experience with the Benelli Sei mirrored the current one of the Quattro. The intake manifold rubbers were broken/cracked causing obvious air leaks. On the Sei, I ordered up OEM Honda manifolds and installed a set on the Sei, which did not have the original airbox in place. The manifolds were a little longer than the originals, but it didn’t matter because of the pod filter installation. The Quattro carb/manifold/airbox combo is a REALLY tight fit; even worse than a standard CB500-550 setup.
Sadly, after the long wait for the box of parts from Germany, it became obvious that the intake manifolds shipped were of two types/lengths. Three might have been actual Sei units and one an actual Quattro replacement part. A message back to Germany, accompanied with photos, confirmed the mistake and a promise to ship the correct parts came back quickly.
Eyeballing the manifold situation, it seemed that the “wrong ones” could be used in the interim but because they were of a thicker material the original manifold clamps wouldn’t reach around to fit the increased diameter. Also, the process of wedging the carburetor rack in between the bolt-on manifold stubs on the head it became apparent that there was left no room for the carburetor rack to fit between the two components. I would imagine that the “correct” way to remove/replace the carburetors is to loosen the engine mounts and tilt it forward, which is required on a CBX Honda Six.
To override that necessity, I removed the manifold stub bolts and replaced them with bolts, so I could slide the whole assembly in laterally and fit the carb inlets to the new air cleaner box connectors. I could only use 2 of the original rubber manifold clamps on the one correct manifold that was supplied, so the other three were clamped with 2” hose clamps that I had on hand. The two rubber manifold types have different ribbed patterns, but they were close enough to allow a tight fit once paired with new clamps.
Another couple of hours were spent doing R&R on the meter box installation, which was a snug fit for all the components. All the wiring connections to the instrument warning lights needed to be disconnected so the harness could be pulled through the small slit on the bottom of the meter box housing. The wiring diagrams found online were all in German or Italian and of very faint and small drawings. That had to be reworked on the computer and printed out to help with the wiring installation. The recommended replacement Yuasa battery had side posts instead of top posts, so some angled adapters were fabricated. Fortunately, apart from some blown-out bulbs and some that had melted the plastic upper meter housing plate, the electrics mostly came to life without blowing any fuses. The fuse block is typically mid-20th Century design with little bullet-ended ceramic fuses and flimsy fuse holder tabs. Corrosion had built up on the ends, so everything needed cleaning to promote good electrical connectivity.
The ignition points were corroded, so required more cleaning and adjustment. I hesitantly tried the starter button and the engine began to spin over, somewhat slowly, but the result was encouraging.
The fuel tank was cleaned and sealed with 2 part Caswell epoxy coatings. New generic Italian-style petcocks were located and installed to complete the fuel tank repairs. Some ¼” T fittings were purchased at the auto parts store and little pieces of 5.5 OEM Honda fuel line were cut up and fitted to tie the fuel system components together.
Initially, the engine spun over, but wouldn’t fire up, even with the choke fully applied. There is a lot of friction with new pistons/rings and a lack of ring sealing in the beginning which caused some difficulties in getting the engine spun over fast enough to get everything synced up, but with a jumper system in place, the long-dormant engine finally fired up on all cylinders, sounding quite like a copy of a Honda CB500 Four with 4 into 4 exhaust pipes. The carbs were fussy, at first. The idle speed was erratic, either too low or too high, probably owing to a sticking spark advancer unit.
The engine does start and run, but not idle well. The charging system light stayed ON, so the left generator cover was removed for inspection. The Bosch charging system uses a set of brushes to contact the slip rings on the end of the rotor shaft, not unlike an automotive alternator. While the components all appeared to be in good condition and electrical wiring checked okay, the whole outer brush/stator assembly was basically just floating on the end of the rotor shaft because the four 5mm mounting bolts were MISSING! Long 5x45mm bolts are not easily found locally, so a quick look online gave some clues about where to find them. I called local hardware/bolt stores and discovered that there were some in stock… 45 of them in a box! I only needed 3, but the whole box was only $6 and change, so I bought the box and have more than 40 to share with anyone out there who might need such a fastener.
The bike continued to be hard starting, didn’t want to idle and one carburetor began to overflow due to a failed plastic float assembly. Carb kits were ordered and the wait continues for replacement intake manifold rubber connectors. All the spares will go with the bike, which has been put up for sale now.
As has happened several times in the past, I am facing surgery again, this time for a worn-out ankle. The recovery requires 3 months of non-weight bearing on the right foot, so getting this project wrapped up and ready for sale has become a race against time.
A quick trip to the CHP office for verification and then back to DMV to push through the completed paperwork was successful, so the bike can be officially titled in the state of California. Having a titled bike helps the sales process immensely so I always do the legwork to get the paperwork in order for the next owner.
I have to promise myself NOT to repeat this process again, especially with another rare Italian Honda copy model, such as the Quattro 500. In an eerie coincidence, during the Quattro project, I was contacted by a man who I met at the January 2018 Mods and Rockers ride event. He had bought a storage unit full of bikes, including a silver 1976 Benelli Sei! He wasn’t going to sell it right away (although there is always a price that works in the end), but needed someone’s help to get his running properly. I offered to help, but warned him of my upcoming surgery and lack of ability to do motorcycle work for at least three months afterwards. Unfortunately, the sands of time have about run out on that offer…
Bill Silver aka “MrItalianHonda” for the end of 2018.