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Ducati 750GT : Dr. Taglioni’s First Twin

As the 1970s opened, it was clear Ducati needed a best seller, purpose built for the American market. It could be argued that Ducati’s current success is due in part from that impetus from the USA to build the Ducati 750GT – the company’s very first twin.

Through the 1960s, the European motorcycle industry underwent a massive shift. At the beginning of the decade, most European riders wanted small commuter bikes, scooters, and the more affluent, sports machines of a half litre or so. By 1970, the world motorcycle market was very different. Most commuters had switched to cars, and motorcycles were now classed as “recreational vehicles,” and the most important class was the 750cc bikes. More than a few makers failed to adapt and passed into history.

In the US, Japanese imports got bigger and faster, challenging the home-grown big-inch V-Twins with more features and performance at a fraction of the price. The Honda 750-four was much less the instigator of this trend than the inevitable result of it. But its success underlined two important factors: if motorcycle makers were to survive into the seventies, they needed to be selling in the US. And the US market wanted 750s. In 1970, Ducati only made singles, with a 450cc their biggest bike. Though they were some of the sportiest and best regarded on the road, they wouldn’t satisfy the US customer.

It was a nudge from importer Berliner Corp. that led Ducati to the 750GT. Working with limited resources, design chief Fabio Taglioni combined inspired engineering, and a flair for originality to create the broad specification of Ducati’s first twin. 

1973 ducati 750 gt beauty shot orange and black rear quarter angle

Limited resources meant working with existing engine components as far as possible, like the cylinder head design and valve train from the singles. Taglioni’s formidable engineering experience allowed him to create an engine that would optimize the use of these components in a relatively untried layout—an in-line 90-degree V-Twin. Taglioni started work in early 1970, and a prototype Ducati 750GT was on the road by August.

The advantages of Taglioni’s engine layout were almost perfect primary balance to minimize engine vibration; and a very narrow frontal section to reduce drag. The disadvantages: a wide V-angle meant having one cylinder pointing almost horizontally forward, stretching the wheelbase. Taglioni mitigated this problem by creating a compact power unit with gear primary drive and vertically stacked gearbox shafts to keep the engine as short as possible. At the same time, the GT’s relatively long wheelbase contributed to its legendary straight-line stability and unshakeable cornering.

The production 750GT was launched in June 1971. Taglioni’s twin was fitted into a frame inspired by Colin Seeley’s race bikes, with the engine as a stressed member hung beneath a steel tube spine frame. The engine used cylinders and heads similar to the singles, but with coil valve springs instead of hairpins. The two connecting rods ran side-by-side on roller bearings and shared a common crankpin on the built-up crankshaft. This ran on roller bearings, but with additional ball bearings in the outer engine casings. Drive to the five-speed gearbox was by helical gears. 

1973 ducati 750 gt beauty shot orange and black right side

The primary and timing gears ran inside a pair of handsome “round” cases (as opposed to the later 900 engine’s “square” cases). Carburetors were initially Spanish-made 30mm Amal Concentrics, with ignition by points driven by a spur gear between the two cylinders. The front cylinder exhausted to the right and the rear cylinder to the left, feeding a pair of Conti mufflers.

A leading axle 38mm Marzocchi fork (embossed “Ducati”) provided front suspension, with a tubular steel swingarm and dual three-way adjustable Marzocchi spring/damper units at the rear. Braking was by a single 279mm disc at the front with twin-piston Lockheed caliper, and by a 200mm drum at the rear. The wire wheels ran on Borrani alloy rims. Atop the handlebars sat paired Smiths tachometer and speedometer in a neat black binnacle.

Competition in the 750cc class was pretty stiff in 1971 when the Ducati 750GT went to market. While the GT’s 57 hp was similar to the contemporary Norton Commando and the Honda 750-four, its MSRP of $1,995 made it $400 more than the Norton and $500 more than the Honda. Then, in 1972, the Kawasaki H2 arrived with 74 hp at an MSRP of under $1,400. However, at 407 pounds dry, the Ducati was the lightest of the bunch, by around 20 pounds compared with the Norton and Kawasaki, and as much as 70 pounds less than the electric-start Honda.

Where the GT really scored over its competition was on the street and track. Taglioni had been careful to ensure the crankshaft was exactly halfway between the wheel axles and on the same level—what we might call “mass centralization” today. 

The gear primary also meant the engine ran “backwards,” partially neutralizing the gyro effect of the wheels, meaning changes of direction were quicker. Combined with the stiff frame, substantial fork, rigid swingarm mounted on large diameter bronze bushes, and lightweight wheel components to minimize unsprung weight, the GT handled beautifully—in spite of the long 60-inch wheelbase and lazy 29-degree steering angle. “…you know a motorcyclist designed this machine,” wrote one American motorcycle magazine “and he got it right.” Other commentators concluded that no bike in the world handled better.

The proof of Taglioni’s genius came in April 1972, when, in spite of giving away plenty of horsepower, the GT-based 750SS achieved a 1-2 finish at the “European Daytona’ Imola 200 race with Paul Smart and Bruno Spaggiari riding. But with the introduction of the 750 Sport in 1972 and desmo 750SS in 1974, the GT took a back seat in the Ducati line up. 

Development continued, though. By 1972, Dell’Orto 30mm pumper carbs had replaced the Amals, and in 1973, Smiths instruments were replaced by Veglia. A Ceriani center-axle fork replaced the Marzocchi. Radaelli steel rims replaced the Borranis, and finally a center-axle Marzocchi fork replaced the Ceriani. Scarab calipers replaced the Lockheed items, in turn replaced by dual Brembo discs. In response to US noise and safety requirements, a steel gas tank replaced the original fibreglass and Lafranconi mufflers replaced the Contis.

But the Giugiaro-designed 860GT of 1974 was scheduled to replace the 750GT, the larger capacity intended to replace some of the horsepower lost through tighter noise regulations, and to accommodate a left-side shifter now required in the US. Apart from a batch of 40 GTs built to order in 1978, production terminated in 1974. George Dockray restored the 1973 Ducati 750GT shown here.

By Robert Smith Canadian Biker Issue #323

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