Honda's Ultra-Rare Sandcast CB750 Prototype

The Honda CB750 Sandcast Prototype

In early 1969, Honda's guys hand-built four CB prototypes. Three are gone. This is the story of the fourth.

At first glance, it could be any first-generation, Candy Blue-Green Honda CB750. But if you know CB750s, and you look closely, you’ll see things that simply do not jibe. Obvious items such as the front master cylinder and brake caliper are different than the expected pieces. Engine covers and rough-cast carburetors aren’t the same, either. And if you could peer into the big four’s cases you’d see a hand-made billet crankshaft—certainly nothing like the production item.

The realization would then hit you: This isn’t just any first-gen CB750. What it is, really, is the father of all CB750s—a hand-assembled prototype (using non-production parts) of one of the most important motorcycles ever built. And that makes it very, very special indeed.

Vic World with his 445-mile sandcast CB750—used for reference to ensure that his restorations are perfect.

Vic World knows a thing or two about special CB750s. As the proprietor of World Motorcycles, and the guy who builds what are considered to be the finest restored sand-cast CB750s on the planet, World knows as much as there is to know about these legendary machines. Honda Motor Company agrees, having acquired two of his restorations, one of which sits proudly in its Collection Hall museum.

“I’ve been around a lot of these things,” World says, “but this prototype really blows my mind.”

Signal stalks are brazed on. Truly a one-off machine.

The story begins six or seven years ago, when one of World’s friends called and said he’d found something interesting while poking around a dealership back East. What World’s buddy found was a rough-condition rolling chassis and a few boxes of engine parts—parts that seemed mysteriously different from production items. The friend immediately suspected a prototype or pre-production CB750, which made sense given the shop’s longtime connection with American Honda. World had him send photos, which proved their hunches correct: This was clearly not a production motorcycle. But what was it exactly?

The bike was wonky in the extreme. It had a king/queen seat in place of the stock piece (which sat on a ’71 CB750 parked nearby), and the engine was a mess, the bottom end still in the chassis and the top end an oily pile of engine covers and torn gaskets in boxes scattered on the floor.

Still, it was quite a find—perhaps the most rare CB750 on earth—so World’s buddy bought it. Over the next couple of years, the friend realized the project was quite a bit more involved than a simple rebuild job. World had offered to buy the bike, and little by little, the idea began to make sense in the friend’s mind. Finally, a deal was made.

“I paid good money for this thing,” World says, “but it was so worth it.”

Everything’s non-standard here, including cam cover and cylinder head. World had to make gaskets from scratch.

As far as World can tell, the shop had tried to get the bike running at some point. It was apparently leaking oil, and they’d tried to make stock gaskets work. But because the engine covers weren’t production-spec, stock gaskets didn’t fit. They even machined the cam covers, to try to make the stock gaskets work, but failed.

“At some point they just gave up,” World says. “And that’s probably why such a rare and important bike came to be tossed into a barn in such rough shape.”

World was over the moon when the crated bike arrived at his Central California shop. “It was dirty and rough,” World says, “but I was really excited. I mean, here was a bike that was hand-assembled and fettled by Soichiro Honda’s very best engineers. It’s the father of the bike that started the entire superbike industry.”

World put the rolling chassis aside and went through the boxes, figuring out what was missing, what was good, bad, or different, and then repacking and labeling everything. “I was amazed at what I found,” he says. “Just as the photos showed, this motorcycle was built from parts that were not standard; most were quite different.

It looks production but isn’t. Check out the non-standard bar and funky master cylinder. Honda toyed with a lot of details before finally putting the CB750 into production.

“Once I saw what I had,” he continues, “I began figuring a plan. A full restoration was never an option; the bike was far too important and valuable to repaint and re-plate, and it was actually in pretty good shape, paint included. There were parts that needed fixing—the brazed-on signal stalks and ill-modified cylinder covers, for example—and the engine needed to be sealed properly. But it was mostly there.”

World decided to basically strip the prototype to its component parts and rebuild it slowly, only fixing things that really needed attention, cleaning—and making functional—every single part on the bike.

“I started with the engine because I figured it would be the biggest hurdle,” World says. “Just making gaskets took the better part of two weeks. First I made paper and cardboard templates of the surfaces then transferred those to gasket material. It was painstaking. Only one gasket that came with the bike worked; the rest needed to be made from scratch. I studied the engine’s oiling system, too, which is different than the production bike.

“I was glad the bike leaked like a sieve at the dealership,” he says. “If it hadn’t, it wouldn’t have ended up in that barn, and I would have never gotten my hands on it. I knew it was likely the bike would never come apart again, so I freshened the well-worn top end with a rebore along with new rings and pistons.” As he worked, World photographed the many non-stock internal parts, some of them placed next to a stock component for comparison’s sake.

Most engine parts are non-stock, which means Mr. Honda’s R&D guys assembled them before production tooling was finalized. The one-off 26mm carburetors and billet crank really make the point.

“The 26mm carburetors [stock size is 28mm] are bizarre,” World says. “Keihin made special dies, and they look sand-cast but aren’t. They also lack air jets and use fuel-metering jets in front of the slides instead. Really oddball, but that’s how prototypes often are.”

Next came the chassis refresh, which was a piece-by-piece process starting with the frame, which was cleaned and checked thoroughly. “The only components that weren’t taken down to individual parts were the wheels,” World says. They were in great shape. Besides the one-off hubs, the front uses a 36-hole rim, which is unlike any other street-going Honda front rim, which are all 40-hole.

“There’s so much handwork on this bike,” World says. “Take the fenders, for example. You can still see the scribe marks under the chrome where the engineers scribed the drill holes; same with the battery box, the seat hook assembly, etc. You just know they were in a hurry to finish these four bikes; the clock was ticking, and they had a deadline for bike shows and magazine impressions in late ’68.”

One big obstacle was the fuel tank, which had been dented when the bike had been dropped at some point in its history. “As I said, repainting it was a no-no, but I also didn’t want that dent showing if I could help it,” he says. “So I contacted a paintless dent repair specialist, who made some special tools that allowed him to get inside through the filler hole. He fixed the dent without a drop of paint, and if you didn’t know it was there, you couldn’t tell!”

Was World considering selling the bike while he was renewing it?

“At first I was thinking more about how special it was and wanting to do a good job on the refresh,” he says. “I mean, this is an extremely rare and important motorcycle. I wanted it to run and be as perfect as it could be visually. But eventually, yeah, I knew I’d sell it. It’s too valuable to sit in my shop where no one would see it. And it’s too rare and important to ride.”

Of course, World did want to ride it, if only for a few miles. “I wanted to hear it run,” he says, “but I also felt it was important to ride it. As the temporary custodian of this bike, and the person responsible for making it right, I felt it had to run—and run well.”

With a bit of choke, the bike fired immediately, which brought a sly smile to World’s face. “It didn’t smoke a bit and warmed up pretty quickly,” he says. “When I took off, the rear wheel spun immediately. The tires, which were original, and which I didn’t want to replace, were rock-hard; you could barely lean the bike over. The other surprise was the bike’s power right off the bottom. I’ve ridden hundreds of these things, and this was the punchiest down low by far. I’m sure the faster intake velocity of the smaller-bore carburetors is to blame. The stock 750s are much mellower, and I’m guessing the factory went with the larger 28mm carbs to smooth things out.”

With nearly 5,300 miles showing, this prototype got ridden plenty before being tossed into a barn.

World also found the brakes lacking in a big way. “The prototype’s discs are polished stainless, while the stockers are ground,” he says. “Not sure if it was the discs or the 45-year-old pads—probably both—but the thing did not want to stop!”

Eventually, World decided to let the bike go and used eBay Motors to get the maximum worldwide exposure. The 10-day auction this past February garnered some amazing numbers: The opening bid—placed by World—was for $1,969, wholly appropriate given the bike’s roots. Within two days, bidding stood at $120,000, where it stayed for a week. On the final day, with just 22 minutes left, it jumped to $135,000. With two minutes left, it went to $142,000, and then, finally, to the winning bid of $148,100. The auction generated nearly 100,000 page views, 102 bids from all over the world, and an astounding 5,243 people “watching” the auction—all huge numbers for an eBay motorcycle listing.

“Since the auction, CB750 enthusiasts have come out of the woodwork,” World says. “My email and phone have been on fire, and some of the questions have made me crazy. But it’s been nice to see all the renewed excitement.”

And that’s an appropriate word. For if the first-generation CB750 generated anything back in early 1969, it was just that: excitement. And it all began with this very bike.

Vic World with his 445-mile sandcast CB750—used for reference to ensure that his restorations are perfect.

Most engine parts are non-stock, which means Mr. Honda’s R&D guys assembled them before production tooling was finalized. The one-off 26mm carburetors and billet crank really make the point.

Signal stalks are brazed on. Truly a one-off machine.

Rods, shift drum, and cam-chain tensioner are obviously different. Most engine parts are non-stock, which means Mr. Honda’s R&D guys assembled them before production tooling was finalized.

Everything’s non-standard here, including cam cover and cylinder head. World had to make gaskets from scratch.

It looks production but isn’t. Check out the non-standard bar and funky master cylinder. Honda toyed with a lot of details before finally putting the CB750 into production.

With nearly 5,300 miles showing, this prototype got ridden plenty before being tossed into a barn.

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