The L-twin is a naturally aspirated two-cylinder petrol engine by Ducati. It uses a 90-degree layout and 270-degree firing order and is mounted with one cylinder nearly horizontal.
The next new Ducati engine to appear after the Ducati Apollo was the 90° V-twin, initial Grand Prix racing versions being 500 cc, and the production bikes were 750 cc. There was also the Ducati 750 Imola Desmo that won at Imola in 1972. These engines had bevel gear shaft drive to the overhead camshaft, and were produced in round, square, and Mille crankcases. In the 1980s, these gave way to the belt drive camshaft engines that have continued to this day, in air-cooled and liquid-cooled form. The Mille used a plain bearing crank, like the belt models.
Engines
V-twin or L-twin
A two-cylinder engine with its cylinders aligned in two banks radiating out from the crankshaft, forming a V angle, is called a V-twin. The Ducati V-twin has the V tilted forward, so the front cylinder is nearly parallel to the ground, hence the term L-twin.
Two-valve engines Ducati engineer, Fabio Taglioni, once said that when they started building the plain bearing crank, belt-driven camshaft engines, instead of the old ball bearing crank, bevel geared shaft drive camshaft engines, he had gone from making complex engines to making simple ones.
Multivalve models From 1987 there have also been Ducati multivalve motorcycles.
History On March 20, 1970, Fabio Taglioni made the first sketches for the layout of a new Ducati V-twin. By April, his drawings were completed, and by July, there was a running motor. By August 1970, there was a complete prototype motorcycle. Taglioni engaged Leopoldo Tartarini, the founder of Italjet, to refine the styling aspects of the new Ducati.
In October 1970, the decision was made by Ducati to re-enter the motorcycle competition. Director Arnaldo Milvio and General Manager Fredmano Spairani, were enthusiastic about racing, and had encouraged Fabio Taglioni to develop the 750 V-twin. In 1971 five 500 cc V-twins were built to compete in the Italian championship and Grand Prix events. Ducati felt that this would demonstrate the bike before a large audience and gain publicity. If they won, that was a bonus.
Even before this, in late 1970, and despite Taglioni's opposition to the idea, Spairani wanted the frame for Ducati's racer to be built by Colin Seeley, a well-known British specialist frame builder of the time. Seeley was asked to develop a racing frame similar to those he had built for G50 Matchless engines. They sent some prototype crankcases for Seeley to work from. Ducati's new Seely frame was ready in February 1971.
Meanwhile, in less than six months, Fabio Taglioni and his team had designed and built their own complete bike (the industry norm for a concept to production is three years). While the 750 and 500 racers were very similar, the 500 had a much shorter 58 mm stroke with its 74 mm bore. It had 10.5:1 compression and initially produced at 11,000 rpm. (Same bore and stroke as the later 500 Pantah) All Ducati's 500 cc GP engines used desmodromic two valve heads with an 80-degree included valve angle. They used remote float bowl Dell'Orto 40 mm carburettors, and had a six speed gearbox with a dry, multiplate clutch. Ignition was electronic, provided by nearby Ducati Elettrotecnica, but was initially unreliable. Dual spark plugs were used, and the final ignition system used four coils, two on each side of the frame.
In the beginning, Taglioni's Ducati chassis was used. It had a single Lockheed front disc brake and a twin leading shoe Fontana rear drum brake. Dry weight was 135 kg, and it had 18in rims front and rear with 3.00 and 3.25 tyres. Wheelbase was 1430 mm. In June 1971, Phil Read tested the 500 cc bike with the Seeley frame, and pronounced it the better of the two. The frame was then fitted to Spaggiari's bike as well. It was raced in 1972 by Bruno Spaggiari, Ermanno Guliano, and Phil Read.
Also, in June 1971, the first Ducati 750 GT models came out of the factory, distinguished by silver frames, metal-flake paint, fibreglass fuel tanks, 30 mm Amal carburettors, and twin leading shoe rear brakes. Taglioni experimented with four valve heads at this time, but failed to produce better power figures than his two valve heads, so the two valve racers continued. He continued to experiment with four valve heads right up to 1973.
In 1971 race results were spoilt by a run of gearbox and ignition problems. Phil Read's second to Agostini in the San Remo Grand Prix, and a fourth, also by Read, at Monza in the Grand Prix delle Nazione were the highlights of the season. A Seeley frame 750 cc had been tested by Mike Hailwood at Silverstone in August 1971 with a view to competing in Formula 750. Hailwood decided against it, saying he didn't think the handling was good enough. Taglioni had already produced a new frame, for the production bike, incorporating some of the Seeley features. He later said he felt the Seeley frame had been too light for the V-twins. They used the production frame for the 1972 Imola bikes.
The 200 Mile formula was first ro run in Italy in 1972, at Imola. Ducati prepared eight 750 cc bikes for the event. Paul Smart, Bruno Spaggiari, Ermanno Giuliano, and Alan Dunscombe were secured as riders. By now, the racing fever had set in, and the factory wanted to win. The bikes had the new factory frames and 750 engines, and were once more prepared in a very short time. Wherever possible, the bike was lightened, and new 40 mm Dell'Orto carburetors with accelerator pumps were used. These engines delivered at 8,500 rpm. In that Imola 200 held in April, Smart and Spaggiari came in first and second."Italian Motorcycles 4" magazine, Article: P28 - P33, "Baby Boomers", Subtitle:"Remember when Ducati went 500 GP racing?" Author: Ian Falloon. Publisher: Federal Publishing Company NSW Australia. The effect on Ducati sales was remarkable. Suddenly, a lot more people the world over knew about Ducati.
The current production 750GT now had a black frame, a new seat, and a red or black paint-job.
Racing success did not last long once Agostini's bike was improved. In May 1972, Bruno Spaggiari finished third in the Italian Grand Prix at Imola, with Paul Smart in fourth, reversing their finishing order in the 200 of a month before. Now the twin could not match Agostini on the MV triple.
Taglioni turned to fuel injection. Direct injection was tried on the 500 grand prix bike at a test session at Modena in March 1972. It was outlawed by the FIM as a form of supercharging soon after. By 1972 the racing bikes had Lockheed twin front discs with a single Lockheed rear disc. Unique leading axle Marzocchi front forks were used. In 1972 a three-cylinder 350 cc 12 valve dohc engine with a seven speed gearbox, was developed, based on a British Ricarclo engine. Fortunately for V-twin fans, it was not competitive.
The 1972 Ducati 750 Sport was released, initially using the 750GT frame with the wider seat section and upper rear shocks in line with the frame, but this was soon changed to a frame with a slimmer rear and the upper rear shock mounts outside the frame. While many components were still shared between the Sport and GT, the main differences were narrower fuel tank, bum-stop rear seat cowl, clip-on handlebars, and rearset foot controls, all giving the Sport its distinct racer persona. The Sport also had blacked out crankcase, 32 mm Dell'Orto carburettors, single seat and sports fuel tank. As with the 750 GT, Tartarini was the styling consultant. At the same time the single-cylinder street racer models were given a restyle, and a matching paint job to the 750 Sport"Italian Motorcycles 4" magazine, Article: P46 - P55, "Round Case", Subtitle:"The story of Ducati's first 750s" Author: Ian Falloon. Publisher: Federal Publishing Company NSW Australia.
The last iteration of the 500 racer appeared during 1973, with belt driven double overhead camshafts, and a radial finned front cylinder. The camshaft belts were on the opposite side to the bevel gear shaft drives on earlier engines. The engine had been developed for Taglioni outside Ducati by Armaroli, and featured the reversed head layout found in the later Paso where the inlet ports face each other. It produced at 12,000 rpm, not a big increase. MV continued to win. In 1971 and 1972, the 500s, and later the 750s, were raced and displayed throughout the western world as part of a major publicity exercise to promote the Ducati name.
In 1973 there was a disastrous change of management personnel. The new boss was De Eccher. All racing projects, including the 500 four, 350 triple, and the 500 GP V-twin, were scrapped. Production was to end for the round case 750 models and all the single-cylinder models. Despite Ducati's withdrawal from racing, many privateers, tuners, and independent racing teams continued to campaign and develop their motorcycles.
In 1973 the production Ducati 750 SuperSport model was unveiled, with an Imola kit for the intending racers. The bike was distinguished by its slim green frame, gaping bell mouths on 40 mm Dell'Ortos, half fairing, fibreglass sports fuel tank with clear fuel-level strip down the side, and single seat.“StreetBike's Best Ever Ducatis”, magazine, Article: P53 – P55, “Numero Uno”, Author: Ian Falloon. Publisher: Federal Publishing Company NSW Australia.
By now the GT and Sport had steel fuel tanks. The GT had shorter rear shocks to lower seat height for the American market, but it meant the bike would ground out more easily when cornering. The Amals on the GT were replaced by 30 mm Dell'Ortos with accelerator pumps. This reduced fuel economy a little.
In 1973 the Barcelona 24-hour race was won by Canellas and Grau on a round case Ducati 750 SS converted into an 860 by the use of the Ducati 450 single-cylinder engine's sleeves and pistons. In 1974, the 860 GT went into production. The crankcases had been redesigned by Giugiaro, along with the rest of the bike, with a squared off look, quite unlike the flowing lines of the 750. The new boss De Eccher saw Ducati's future in US exports, and had engaged Giorgetto Giugiaro to do the external design work on the new 860 instead of Tartarini. Taglioni was made to redesign the outer engine cases to match Giugiaro's design. (The new 350 and 500 GTL sport vertical twins were also released, also externally designed by Giugiaro. The motors were not built by Taglioni. He had refused to be involved with them.)
Ducati sales fell. The 860 GTS did not sell well, and the vertical twins were hardly selling at all. De Eccher was out, and Taglioni was back in favour, and so, by association, was Tartarini. A hasty re-design of the fuel tank and seat was undertaken to create the 900GTS - a model destined to help the company regain some ground. At the same time plans were put in place to create two new models the Darmah and the Pantah.