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Ducati 125 Sport

(by Ian Falloon, Feb 2022)

Ducati 125



The market's desire for racer-replica Ducatis has a long history


Ducati’s reputation has always been built on racing success, and it began back in 1955 with the 100cc Gran Sport.


After the Laverdas soundly beat the overhead valve Ducati 98s in the 1954 Motogiro d’Italia and Milano-Taranto road races, Ducati lured the great engineer Ing. Fabio Taglioni away from Mondial and commissioned him to design a new motorcycle capable of winning the 1955 Motogiro.


The result was the magnificent Gran Sport, or Marianna. This advanced design formed the basis of the all the overhead camshaft singles through until 1974, with many of its design characteristics continuing to feature on some of the current engines.

After the humiliation of 1954, no-one could have predicted the success of the Marianna in the 1955 Motogiro d’Italia.


The Mariannas were unbeatable, Taglioni’s one-year contract was extended, and his association with Ducati would last four decades.


The basis of the Gran Sport engine was its vertically split aluminium unit construction crankcase, aluminium cylinder (with cast-iron liner) inclined forward 10 degrees, a single overhead camshaft driven by a set of bevel gears from the crankshaft, and two valves set at an included angle of 80 degrees.


All the bearings were ball or roller and incorporated in the crankcases was a four-speed gearbox, driven by primary gears with a wet multi-plate clutch. Ignition was by battery and coil with the points driven off the lower bevel gear on the right. This engine was then placed in a single downtube tubular steel frame and was utilised as a stressed member, all these features making their way to the eventual production version, most also evident on all single and twin cylinder Ducatis though until 1980.


The success of the Gran Sport was such that Taglioni was allowed to adapt his advanced single cylinder overhead camshaft engine for production. Initially 175cc, most motorcycles of the period still featured overhead valves operated by pushrods, and while there was little to separate the OHV 98s and 125s from dozens of other Italian motorcycles available at the time, the overhead camshaft 175 provided exceptional performance.


The 175 was first displayed at the end of 1956, and its success, they accounted for 25 per cent of 175 cc sales in Italy during 1957, saw a proliferation of overhead camshaft models during the next few years.


Only a year after the introduction of the 175, the 125 Sport (1962 model pictured) was offered. Sharing its 55.25mm bore and 52mm stroke with the double overhead camshaft Grand Prix and desmodromic racers, the 125 Sport had an 8:1 compression ratio and Dell’Orto 20mm carburettor and produced a modest 10 horsepower at 8500 rpm. T


his may not have sounded much but the specific power output of 80 horsepower per litre was quite impressive for a production engine in 1958. Rolling on a pair of 17-inch wheels the diminutive 100kg 125 Sport was capable of around 112km/h, quite a bit more than most 125s at the time.


As the styling, particularly the sculptured 17-litre fuel tank, mimicked the racing 125 F3, the 125 Sport became favoured with the Italian boy racer crowd. This was the first production Ducati that looked like the racing bikes and established a formula that has served Ducati well for over sixty years.


As the 125 Sport was proving successful, a low compression 125 TS (Touring Special) joined it later in 1958 but this wasn’t what the market really wanted. The 125 eventually became a 160 but as this was perceived as an underpowered 175 it languished, eventually becoming the unremarkable 160 Monza Junior.


Although the 125 Sport remained a popular model, particularly in Italy, through until 1965, the writing was on the wall for the smaller capacity Ducatis. The public then, as now, wanted larger engines, with more performance, but what hasn’t changed is their thirst for factory race replicas.




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