Motorcycle Classics

Taglioni’s First Twin: 1973 Ducati 750GT

1973 Ducati 750GT
Claimed power:
49.91hp @ 7,200rpm (period test)
Top speed:
125mph (est.)
Engine: 748cc air-cooled SOHC 90-degree V-twin, 80mm x 74.4mm bore and stroke, 8.5:1 compression ratio
Weight (dry): 407lb (185kg)
Fuel capacity/MPG: 4.5gal (17ltr)/35-45mpg
Price then/now:

By 1970, the global motorcycle market was very different from what it had been a decade earlier. In the early ‘60s, most European riders wanted small commuter bikes or scooters, while the more affluent leaned toward sports machines of a half liter or so. Ten years later, 750cc bikes were the most important class: most commuters had switched to cars, and motorcycles were now classed as “recreational vehicles.”

In the U.S., Japanese imports grew larger in capacity and brisker in performance, challenging the traditional American big-inch V-twin with more features and performance at a fraction of the price. The much heralded Honda CB750 Four was less the instigator of this trend and more the inevitable result of it. Perhaps the most important achievement of the CB750 was to reinforce 750cc as the benchmark capacity for new sporting motorcycles: If motorcycle makers were to survive into the Seventies, they needed a 750. In 1970, Ducati made singles up to just 450cc — even if they were some of the sportiest and best regarded on the road.

Creating a 750

It was a combination of limited resources, inspired engineering, business acumen and a flair for originality that led famed Ducati engineer Fabio Taglioni to pencil out the broad specification of Ducati’s first twin. Limited resources meant working with existing engine components as far as possible, such as the cylinder head and valvetrain from the singles. Taglioni’s formidable engineering talent allowed him to create an engine layout that optimized the use of these components in a relatively untried layout; an inline 90-degree V-twin, often called an L-twin. Taglioni started work on the project in March of 1970, and a prototype was on the road by August. The result was the 750GT.

The advantages of Taglioni’s engine layout were almost perfect primary balance to minimize engine vibration, and a narrow frontal section to reduce drag. The disadvantages of a wide V-angle, however, meant having one cylinder pointing almost horizontally forward, so the wheelbase had to be long enough to provide clearance between the cylinder and the front wheel. Taglioni mitigated this challenge 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 long wheelbase contributed to its legendary straight-line stability and unshakeable cornering.

The production 750GT was launched in June of 1971. The twin was fitted into a frame inspired by the Colin Seeley item used on some of Ducati’s GP bikes, with the engine as a stressed member hung beneath a spine frame made up of three steel tubes.

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 on a common crankpin. The built-up crankshaft ran on ball bearings, with additional outrigger bearings in the outer engine casings. Drive to the 5-speed gearbox was by helical gears. The primary and timing gears ran inside a handsome pair of “round” cases (as opposed to the later 900 engine’s “square” cases). Carburetors were initially Spanish-made 30mm Amal Concentrics, with ignition by contact 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 “Ducati” embossed Marzocchi fork provided front suspension, with a tubular steel swingarm and dual three-way adjustable Marzocchi shocks at the rear. Braking was by a single 10.8-inch disc at the front with a twin-piston Lockheed caliper, and a 7.9-inch drum at the rear. The wire spoke wheels ran on Borrani alloy rims.

Class wars

Competition in the 750cc class was pretty stiff when the 750GT went to market in 1971. While the GT’s claimed 57 horsepower was similar to the contemporary Norton Commando and the Honda CB750 Four, its MSRP of $1,995 made it $400 more than the Norton and $500 more than the Honda. In 1972, the 750cc Kawasaki H2 arrived with 74 horsepower at an MSRP of less than $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 to achieve what we might call “mass centralization” today. Combined with the stiff frame, the substantial fork, and the rigid swingarm mounted on large diameter bronze bushings and lightweight wheel components to minimize unsprung weight, the GT handled beautifully — even though the long, 60-inch wheelbase and 29-degree steering rake made it slow to turn. “You know a motorcyclist designed this machine,” wrote Cycle magazine, “and he got it right.” Most commentators conceded 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 came first and second at the Imola 200 — the “European Daytona” — with Paul Smart and Bruno Spaggiari riding. Yet with the introduction of the 750 Sport in 1972 and the “desmo” 750SS in 1974, the GT took a back seat in the Ducati lineup.

Development continued, however. By 1972, Dell’Orto 30mm pumper carbs had replaced the Amals, and in 1973, the Smiths instruments were replaced by Veglia units. A Ceriani center-axle fork replaced the Marzocchi fork, now carrying a Brembo brake caliper. Radaelli steel rims replaced the Borranis, and forks changed again, a center-axle Marzocchi fork replacing the Ceriani. In response to U.S. safety and noise requirements, a steel gas tank replaced the original fiberglass tank and Lafranconi mufflers replaced the Contis.

But the 750GT’s time was almost over. The Giugiaro-designed 860GT of 1974 was scheduled to replace it in the Ducati lineup, the larger capacity intended to mitigate some of the horsepower lost through tighter noise regulations. The 860GT also accommodated a left-side shifter now required in the U.S. Apart from a batch of 40 GTs built to order in 1978, production terminated in 1974.

George Dockray’s 750GT

Vancouver, British Columbia’s George Dockray found his 750GT as a rolling basket under a pile of blankets in an auto detail shop. “Except it wasn’t rolling,” George says. “The brake caliper had seized.” The engine was out of the frame and completely disassembled — even down to the crankshaft being separated. The reason for the engine strip soon became apparent: the crankcase had been damaged around the countershaft sprocket, presumably by a broken chain. The case had been nicely repaired, but that was as far as the previous owner had gotten with the rebuild. The cylinders were also missing.

Faced with trying to reassemble the engine from boxes of parts, including the bevel-drive engine’s notorious multitude of gears, sprockets and shims, George decided instead to entrust the job to legendary Ducati bevel guru Guy Martin at Martin Brickwood Performance in Pointe Claire, Quebec. That left him to deal with the “rolling” chassis.

The seat and exhaust were missing, the taillight was incorrect and one of the footpegs was from a Ducati single. The instrument panel had one Smiths clock and one Veglia. So began the process of cleaning, repairing and replacing parts. Some of the pieces George needed were available from California specialists Bevel Heaven, and George found he could source many of the parts economically from Canada, Europe and Australia. Laverda specialists Columbia Car & Cycle in Nakusp, B.C. had a useful selection of parts, including carburetor parts, sprockets and an excellent seat cover. Many components also came from Ducati Classics in the Netherlands, and a smaller number from Mdina Italia in the U.K. Brancato Engineering provided a rare-earth-magnet oil strainer, and also sells trick Ducati special tools. A reproduction kick starter shaft came from Unmüssig Motorradteile in Germany, a new dashboard came from Australian motorcycle rubber specialists Bevel Rubber, and a new brake disc from Gowanloch, also in Oz. Replacement cylinders came from Advanced Motorsports in Dallas, Texas.

Once the engine came back from Martin Brickwood, George tackled the assembly. It was after the bike was mostly together and he tried to fit the rear fender that he realized things weren’t as they should be: the frame was out of alignment. Fortunately, with some judicious application of hydraulic pressure, the frame was straightened without having to remove the engine.

George thinks his bike was originally built in 1972, though it’s registered as a 1973. The tell-tale is the early-type two-piece front wheel hub. As a rider, he’s more interested in practicality than originality: The large basket-type air filters aren’t stock — early GT’s used open bellmouths — and the Hella-style bar-end turn signals aren’t original, though they were period accessories. “The purists go ballistic,” George says.

Riding the 750GT

George had ridden a 750GT before, back in the Seventies, so he had an idea of what to expect. “I got to take one around Road Atlanta,” he says. “They were expensive then.” He remembers the GT being a slow-steering bike with geometry, though it compared reasonably well for the period. But the bike he’s just finished building seems better than he remembers. “It doesn’t seem quite as bad as I thought,” he says. “I chose a narrow front tire, a 90/90 section instead of 100/90, but it does take a deliberate effort to set up for the corners.”

George has replaced the original master cylinder with one of a smaller diameter to improve its “wooden” feel, and uses Ferodo Platinum brake pads. He has also tackled one of the other criticisms sometimes leveled at the 750GT, a stiff clutch lever, by using an extended operating lever.

So what really stands out for George when riding his rebuilt bike? “How smooth it is,” he says. “The engine doesn’t seem to mind high or low revs — it’s just smooth everywhere. The sound is wonderful, though I wish it was a little quieter,” George says, noting that there’s also a fair amount of mechanical noise. Yet he’s impressed by the engine’s broad powerband. “The spring valve engine is in a relatively mild state of tune, and it’s really torquey. It’s happiest above 4,000rpm, but you can be at shifting.

“It makes a terrific touring bike. The brakes are OK, but not fabulous,” he notes, “though for the time, they were a lot better than drums. Overall, it’s really nice to ride. It has a balance of subtle characteristics that give it a personality — what Kevin Cameron called ‘super good ride feel.’”

Berliner Motor Corporation

It’s almost certain that U.S. distributor Berliner provided extra impetus for Ducati to introduce a twin-cylinder motorcycle — just as they had sponsored the ill-fated Apollo project a decade earlier. One of Berliner’s goals was to source motorcycles that could compete with Harley-Davidson in the lucrative law enforcement market. They ultimately found success with Moto Guzzi, another brand they represented in America, when the Los Angeles police department selected the V7 Police for their force in 1968. It was the first time a foreign-made motorcycle had won a police supply contract in the U.S.

Joseph and Michael Berliner arrived in the U.S. in 1947, having survived the Auschwitz concentration camp. By 1951 they had established an import business distributing Zündapp motorcycles. Over the next decade they added Ducati, Moto Guzzi, Norton and Matchless. They’re often credited with pushing these manufacturers toward larger capacity motorcycles, including the 750cc Norton Atlas; the 750cc Matchless G15/45; the “hybrid” 750cc Norton P11 and N15 range; the Atlas-engined Matchless G15; and the 750cc and 850cc loop-frame Moto Guzzis.

And while Ducati’s 750GT would probably have made a fine highway patrol machine, its engineering complexity — especially the bevel drive overhead cam — would have led to higher maintenance costs compared with the simple overhead valve Guzzi. MC

  • Published on Apr 9, 2015
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