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DUCATI NARROW CASE SINGLES

Article #1, 31 March 2011 by Harné Heuvelman

The narrow case single cylinder engine marks the beginning of Ducati’s development into a world class manufacturer of sports motorcycles. In 1954 Ducati Mecchanica was ambitious to win races and hired Fabio Taglioni with the assignment to develop a new motorcycle capable of winning the 1955 Motogiro d’Italia.

The result was instant success with the 1955 100 and 125 Gran Sport. Although better known under their nickname ‘Marianna’, this was the first Ducati to have a bevel driven overhead camshaft engine. It laid the basis for further development of all future Ducati single cylinder models until 1974 and, one can argue, also for the bevel drive twin engines until 1986. Fabio Taglioni shaped the future for Ducati by engineering this great engine.

The Gran Sport or Marianna was in fact a racing bike. It was later developed into the Bialbero with a double overhead camshaft, but also sold ‘to the public’ in limited numbers with engine displacements of 100, 125 and 175cc.

The name ‘narrow case’ has only become popular to distinguish this type from the later ‘wide case’ models. The largest difference between the two being that the latter type had wider frame mountings on the crankcases to fit in an improved frame design.

After the success of the Gran Sport, Ducati decided to adapt the design into that of a road going sport motorcycle: the 1956 175 Sport. The engine had a simpler design, using a one piece cylinder head and enclosed valve springs. The remarkably sculptured fuel tank of the 175 Sport was later to be seen on the 200 Elite.

The 175 Sport was a huge success and was further developed into numerous new models like the 175 T, 100 Sport, 125 Sport, 125 Turismo Speciale (TS) and 175 Turismo Speciale (TS) all using more or less the same basic engine and frame layout.

A truly beautiful machine is the Ducati 200 Elite of 1959, produced until 1965. It had a 200cc version of the 175 Sport engine and was sold in the US under the name 200 Super Sport. The bike featured dual chrome exhaust mufflers, aluminium rims (although the first had steel rims) and the same 17 litre sculptured fuel tank as the 175 Sport, but with chrome panels. In its gold, maroon and chrome colour scheme, this motorcycle is arguably one of the prettiest ever made.

Although developed as a 250cc in the ‘special order racer’ 250 Formula 3 in 1959, a road going version was not available until 1961 with the introduction of the touring 250 Monza and sporting 250 Diana. With this development the first major improvements to the engine was undertaken, creating new cast-iron clutch housing with integral bearings, and a longer crankshaft. The 250 Diana had an optional tuning kit with high compression pistons, a Dell’Orto SS1 carburetor and megaphone exhausts. This made the 250 Diana exceptionally fast for its day with a top speed of 160 km/h or 100 mph.

The 250cc engine also became available in a wider range of models in 1962. The 250 Scrambler focused on off-road use and the racing 250 Diana Mark 3. Both models had higher compression, a ‘hot’ camshaft and the Dell’Orto SS1 carburetor making them amongst the most competitive bikes of their era with a power output of 30 bhp @ 8,300 rpm.

In 1964 the 250 Mark 3 (not to be confound with the wide case’ 250 Mark 3 Desmo) replaced the 250 Diana Mark 3 with the largest technical difference being the new five speed gearbox replacing the four speed. The 250 Mark 3 was largely focused on American customers and availability was limited in Europe. Also, it was rather difficult to start as it had no battery and a 40 watt flywheel ignition. Ducati looked for a way to create an improved version for their customers at both sides of the Atlantic. This resulted in the 250 Mach 1, one of the most desirable Ducati’s of all time.

By 1965, Ducati’s racing department was developing at the limit of the single-down tube frame they had been using for so long. The racing version of the 250 Mach 1; the 250 SC was the first to have a double down tube ‘cradle’ frame to cope with the increased power output of the modern engine. The engine had to be adapted to fit the new frame and it was clear that a new frame and engine was needed for road going bikes as well.

The final ‘narrow case’ to be entirely built in Bologna (the Spanish company Mototrans produced the engine until 1974) was the 350 Sebring with was very similar to the 250 Monza but with a bored and stroked engine creating a 350cc. Production of the ‘narrow case’ seized in 1966 to be replaced by the ‘wide case’ in 1967.

Engine

All ‘narrow case’ single engines have a vertically split aluminium crankcase, a forward inclined (10 degrees) cylinder and a single overhead camshaft driven by a set of bevel gears from the crankshaft. The gearbox is integrated in the crankcase, at first a four speed which was later replaced by a five speed in the 250 Diana Mark 3.  

Frame

All narrow case singles have a single-down tube tubular steel frame, using the engine as a stressed member. The engine is mounted using two plates at the front and directly at the rear. Most models have a Ducati 31.5mm telescopic front fork apart from some of the earlier models which had a Marzocchi front fork. Rear suspension usually consists of twin Marzocchi three-way adjustable shocks.

References (recommended further reading)

Falloon, Ian (2004) Standard Catalog of Ducati Motorcycles, Iola: KP Books

Walker, Mick (1985) ‘Ducati Singles’, London: Osprey

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