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 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.