Ducati’s First Generation of L-Twins

Story by Graham Clayton// Photos by Graham Clayton
March 1 2009

By the year 1969, Italy’s Ducati Meccanica Spa had established a solid reputation as a builder of sporting 4-stroke single-cylinder motorcycles, the largest of which displaced 436 cc’s. That year brought a major shakeup in the senior management of the Bologna-based firm as Ducati’s long time general manager Giuseppe Montano was replaced by the new team of Arnoldo Milvio and Fredmano Spairani.

Ducati’s principal owner at that time, the Italian government, wanted to see more innovative and aggressive things from Ducati. The result was Milvio and Spairani getting the go ahead for two major initiatives, namely, the development of a new 750 cc street bike, and secondly the creation of a 500 cc road racer to increase the firm’s visibility in the marketplace.

Ducati’s top export market was the United States. Berliner, the U.S. import distributor, had long been pressing Ducati to produce a larger displacement machine to appeal to the ‘bigger is better’ buying preferences of American bikers. Competing firms, both Japanese and European, were introducing larger capacity bikes, and the Berliner brothers didn’t want to get left behind.

An earlier big bike project pursued under Montano, the Apollo V-4, had turned out to be an unmitigated flop. Targeted at police departments and big bore touring bike enthusiasts, the Apollo was ugly and heavy, and looked likely to generate little buyer appeal.

Milvio and Spairani were now in the hot seat and had to deliver, or else lose their jobs.

Fortunately for them, Ducati’s chief designer, Fabio Taglioni (Dr. T), was enthusiastic about the challenge and well up to the task of designing the two bikes. Both, he decided, would be non-conventional 90 degree V-twins, what he liked to refer to as ‘L-twins’ because of the nature of their cylinder layout.

Taglioni focused on the bread and butter 750 street model first and made rapid progress. In less than two months he had completed the design of the 750, and within a further two months had built and was running the first engine on a test bed. By August the firm had put together a development prototype, the first of four, and was busy conducting shake-down road tests in the hills around Bologna.

Starting in September of 1970, pre-production versions of the new 750 GT as it was to be called, were introduced to the media and put on display at major motorcycle shows to gauge customer response and to get critical buyer feedback.

The 750 engine had a forward-facing front cylinder that was inclined upward 15 degrees from the horizontal and therefore a rear cylinder leaned 15 degrees backward from the vertical. The twin cylinders shared a common crankshaft with pressed-up flywheels and closely spaced connecting rods that allowed for the two cylinders to be slightly offset, about an inch either side of centre. This cylinder layout made for virtually perfect primary balance and little in the way of secondary imbalance, and therefore a very smooth running engine.

It also allowed the use of forward facing exhaust ports on both cylinders with good cooling air flow to the rear cylinder, something that was not possible on most contemporary V-twins, such as those built by Harley-Davidson.

Taglioni incorporated much of the knowledge gained from development of Ducati’s singles, both as a time saver and as a means of reducing both development and production run costs.

The cylinder heads employed bevel gears and vertical shaft drive for the SOHC valve train, as on the singles, but with coil instead of hairpin valve springs to facilitate narrower cam boxes. Rear facing 30 mm Amal concentric carburetors fed 2-valve 8.5:1 compression cylinder heads that vented through a pair of twin Conti megaphone-style mufflers.

The engine employed vertically split cases, a wet sump, forced lubrication via a gear pump, plus a wet multi-plate clutch. Final drive was by chain and used a 5-speed gearbox that was located in the rear right side engine case, same as on the singles.

Ducati switched to the use of 12-volt electrical systems for the twins, a much needed improvement. The 750 GT came fitted with a 150 watt generator and a 40/45 watt headlight. The ignition system was by battery, coil and points, with a single spark plug per cylinder. Starting was via a kick starter located on the right side of the engine.

As Taglioni neared completion of the 750 GT he also began work on the 500 GP twin. This machine shared many design features with the 750 street bike and Taglioni used it as a rolling test bed for further development of the 750. Both SOHC and DOHC cylinder head versions were experimented with, including two and four valve per cylinder variants. Dr. T also experimented with fuel injection alternatives to carburetors.

Ultimately six 500 GP machines were built and raced during 1971-73. These bikes turned in some good results when raced by Phil Read and others, and proved capable of beating all but the mighty MV-3 works bikes in the 500 GP class.

Interestingly, it was a specially commissioned frame built by Colin Seeley for the GP 500 bike that served as the basis for Taglioni’s final frame design for the 750 GT. This was an open cradle design that employed the engine as a stressed component to complete the lower loop.

Running gear on the new 750 consisted of 38 mm leading-axle Marzocchi forks fitted with a 19-inch wheel and a single 280 mm front disc, this grasped by a Lockheed caliper. Twin 305 mm Marzocchi rear shocks were fitted to the rear swingarm that carried a 200 mm drum brake fitted to an 18-inch rear rim. Stainless steel fenders were used front and back.

The fuel tank used on early GT models was a rounded, 17-litre capacity, fibreglass unit. This was mated to a dual saddle and fibreglass side covers. Dual pegs placed relatively forward on the bike were combined with a pair of moderately raised handlebars to make for a very comfortable riding position. The dry weight of the new bike was a modest 185 kg (409 pounds).

The original 750 GT developed 57 horsepower at 7,700 rpm, and had a wide flat torque band that made for effortless running and an easy pull-away from stop signs or traffic lights. Despite having a long wheelbase of 1,530 mm (60.2 inches), the bike had excellent road manners, and thrived on high-speed twisty roads where it could show a clean pair of heels to a CB750.

The 750 GT went on sale in mid-1971, by which time Taglioni had begun work on a higher performance version, the 750 Sport, which became available the following year. The Sport came with an orange-coloured slim-line fibreglass racing tank that carried 19-litres of fuel. It also had a matching orange single bucket racing seat, side covers and fenders, plus rear-set foot pegs and clip-on handlebars.

The black Sport frame was the identical to the GT with the exception of a wider swing arm. The suspension and brakes employed were also basic GT (but for exposed springs on the twin rear shocks).

The 750 Sport motor had a higher 9.3:1 compression ratio, breathed through twin 32 mm Dell’Orto pumper carbs, and put out 62 horsepower at 8,200 rpm. With a dry weight of around 183 kg (400 lbs) the new model was a factory café racer capable of top speeds of 210 km/h (130.5 mph), and became an instant hit.

By now Taglioni was looking to build a racing version of the 750 street bike, something that Ducati could maybe enter in the Daytona 200, and really give Ducati’s big twin a media boost. The only problem with this was that the AMA then had a 200 machine production homologation requirement (200 units built and available for sale), plus a $10,000 claiming rule (whereby someone could lay down $10,000 to claim any bike that won an AMA road race, including full works factory bikes). Neither Taglioni nor Ducati were keen about either of these rules.

Instead Ducati opted to contest the new and nearby Imola 200 F750 event that would be run for the first time in 1972, and which was marketed as the Daytona of Europe, only having an even larger winner’s purse.

Taglioni modified his standard 750 twin motor fitting it with twin-plug desmodromic heads, special Imola camshafts, large 40 mm intake and 36 mm exhaust valves, competition pistons, lighter polished billet connecting rods, straight cut primary drive and clutch gears, a drilled clutch basket, standard gearbox geared for 270 km/h (169 mph) in 5th, twin first–generation 40 mm Dell’Orto pumper carbs, an oil cooler and a high-low (left & right) racing megaphone exhaust system.

Seven engines were pulled off of the production line and given this makeover. The end result was a rear wheel power output of 84 bhp at 8,800 revs, with 70 bhp on tap at 7,000 rpm, and the ability to rev to 9,200 if needed.

Standard frames were employed on all of the works machines, complete with centrestand bracketry, as well as standard 38 mm leading axle forks. Twin 280 mm front disc brakes and a single 230 mm rear disc all fitted with Lockheed calipers provided the stopping power.

Ducati went looking for a top rider for their new 750 desmo, but were turned down by Jarno Saarinen, Renzo Pasolini and Barry Sheene. British Ducati distributor Vic Camp was able to recruit Paul Smart at the last minute after his Triumph triple ride had fallen through. The rest as they say is history.

Pre-race favourite Giacomo Agostini (MV Agusta 750-4) lead the race for the first four laps at which point he was passed by Smart. On the following lap, Ducati rider Bruno Spaggiari also went by Agostini. From there onward the Ducati duo motored away from the rest of the field running together until the last five laps at which point both riders went for the win with Smart coming out on top. The media coverage that Ducati gained from this victory was worth millions and Ducati’s image as a motorcycle manufacturer was transformed.

Ducati quickly built a small batch of replica Imola racers that they sold to select privateer racers. They then directed Dr. T to build an Imola-inspired desmo model for street use. This was the original 750 Super Sport, a genuine 80 bhp (at the crank), 225 km/h (140 mph) street legal racer.

It came with a silver fiberglass half-fairing, Imola gas tank, bucket racing seat and front fender, aquamarine colour frame, Scarab triple disc brakes, 38 mm Marzocchi forks, 40 mm pumper carbs and Conti megaphone mufflers. The bike went on display in 1973 and was sold throughout 1974. This bike, stock versus stock, was 10 km/h (6 mph) faster than the 4-cylinder 900 cc Kawasaki Z-1.

In 1974, Ducati introduced one of its worst received models, the 860 GT with bodywork by car designer Giorgetto Giugiari. This bike had an 864 cc engine, achieved by increasing the twin’s bore from 80 mm to 86 mm. A bored-out works desmo of this displacement won the Spanish 24-Hour race at Barcelona in both 1973 and 1975.

This prompted Ducati to introduce larger displacement versions of their L-twin. The 860 GT was the first, but had harsh straight edge lines for its fuel tank, seat and side covers that few bikers liked. It was also the first model to appear with the squared-off engine cases. Over the next five years, Ducati would repeatedly revise the looks of the non-desmo ‘springhead’ 860 road bike in an effort to boost its sales, before ultimately dropping it from their line-up.

In 1975, Ducati offered the Super Sport model in both 750 and 860 capacities, each now fitted with square engine cases. New government regulations for exhaust noise level, pollution emissions and other requirements, like left-side gear selector, caused Ducati to both revise and take some of the racer edge off of the SS model. Starting in 1976 Ducatis came with left-side gear change and right-side rear foot brake.

By 1976, Ducati realized that they needed something new to bridge the rider gap between the 750 and 860 valve-spring touring twins and the hard to live with SS street racer models. They needed a rider-friendly dual saddle desmo good for both town and country riding. Designer Leopoldo Tartarini was recruited to pen the bodywork, the end result of which was the 900 Darmah model introduced in 1977.

This bike was arguably one of the best-looking bikes built in the 1970s. Offered originally in bright red with white contrast striping, black frame and gold coloured Campagnolo mag wheels, the bike was a stunner. It was also a very comfortable and a solidly performing street mount as this rider learned when he tested a new one owned by a friend.

Fitted with an electric starter, upgraded electrics and a halogen headlight, easy to read Nippondenso speedo and tach, 32 mm Dell’Orto PHF carbs, low-rise handlebars and semi-rearset footpegs, the 900 Darmah was a great street bike. It was smooth running, fast, handled well and had a broad power band. The Darmah used Marzocchi suspension front and back with twin gas shocks, plus a triple disc braking system that made spirited riding much safer.

Ducati went on to develop two further versions of the Darmah, the most memorable of which was the Super Sport Darmah offered from 1978 through 1981. This bike came in a two-tone ice-blue/dark blue colour scheme with a matching half fairing and black frame. SS Darmahs could be ordered with Contis and 40 mm pumpers for those who wanted extra speed over and above the standard model’s 205 km/h (128 mph).

Ducati Super Sport models continued to rack up race wins throughout this period further promoting the racing image of the brand. In 1975, Cook Neilson of Cycle Magazine fame won the 750 production race at Daytona, followed two years later by a runaway victory in the 1977 Daytona Superbike Race aboard the ‘California Hot Rod’.

Arguably Ducati’s biggest race victory with a bevel gear Ducati ‘L-twin’ was Mike Hailwood’s FTT1 (Formula Tourist Trophy 1, an open GP formula class for up to 1000cc 4-stroke racing bikes) victory at the 1978 Isle of Man TT aboard a 900 NCR Ducati prepared by Steve Wynne of Sports Motorcycles Manchester. That win gave Ducati its first world road racing title.

Hailwood’s phenomenal back-from-retirement victory prompted Ducati to introduce the Mike Hailwood Replica 900 in 1979. It came with a red, green and white colour scheme similar to that of Hailwoods racer, plus a full fairing, large fuel tank and racer-type single seat with a removable section that allowed two-up riding. This was very much a limited production model.

To Ducati’s pleasant surprise, the market demand for the Hailwood Replica was so great that the firm homologated the model and put it into volume production. The MHR, as it was called, sold through the end of 1983 as a 900, and was thereafter replaced with the 973cc Mille-engined Mike Hailwood Replica.

The Mille engine was the last, and in many peoples’ view the best version of Taglioni’s bevel gear ‘L-twin’ engine. It incorporated lessons gained from more than a decade of racing experience and street bike refinement. These engines had a hydraulic clutch, a much improved oil pump and lubrication system, better ignition and electrics, electric start, plus numerous other improvements.

My friend and former road racer, Malcolm Tunstall, left a lasting impression with me about the Mille motor at a mid-eighties road race event. During a conversation about the 973 cc motor he said to me, “Watch this”. He reached for the kickstart of his Mille–engined road racer and pushed it down by hand. It fired first push and ticked over steadily. Not bad for a 1,000 cc racing twin.

By 1985, Ducati was once again in financial difficulty. The Castiglione brothers, then owners of Cagiva, purchased Ducati for a reported $5 million in US funds, less than one percent of what they were able to sell it for a little over a decade later. Ducati had discontinued production of all of the bevel gear models save for the MHR and the SB2 (successor to the 900 SS) by this time. The bevel gear engines had reportedly become prohibitively costly to produce and assemble, and were being replaced by the newer and more cost-effective toothed belt-drive overhead cam desmo engines, Taglioni’s second generation of ‘L-twins’.

The last Mike Hailwood Replica Mille rolled off the Bologna production line in early 1986 at the direction of the new company owners. The era of Ducati bevel gear twins production was over.


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