Ducati 125 "Desmodromic"

 

 

 

The Italian Ducati factory was the first to successfully race a motorcycle having a power unit with desmodromically-operated valve gear. This awe-inspiring word hides no mystery—it means that cams are used to push the valves shut as well as to open them; this ensures that valve-bounce (caused at high revs by the valve spring failing to keep its valve in contact with the cam) cannot happen—and so a missed gear-change does not mean a valve through a piston! More important is the fact that valve bounce does not dictate the unit's r.p.m. ceiling.

The machine illustrated is one raced by Mike Hailwood with tremendous success at British short-circuit meetings in 1959 and on which he also achieved his first "classic" victory, at that year's Ulster Grand Prix.

Several other unusual features were employed in this design. A six-speed gearbox was built in unit with the engine. Twin coils fed a pair of sparking plugs, one in the orthodox position and one tucked in front of the camshaft drive vertical shaft.

Although a fairly conventional duplex-loop and single top-tube frame was employed, it appeared to have been built around the motor rather than designed with it; the front down-tubes were kinked in two planes to mate with the front of the crankcase. Sheet steel was used to "box" the upper and lower crown lugs on the telescopic forks in an endeavour to prevent flexing at high speeds over bumpy going (the model would comfortably exceed the 100 m.p.h. figure) but its handling, even in Hailwood's skilled hands, was at best only average.

The factory built a 250 c.c. twin which was virtually a double-up of this model, but it never achieved the success of the eighth-litre machine.

SPECIFICATION
Engine: single-cylinder 125 c.c; three desmodromic o.h.c; drive to camshaft gear train by shaft and bevels.
Ignition: twin coils to two plugs.
Transmission: gear primary drive to six-speed gearbox in unit with engine; final drive by chain.
Frame: duplex cradle with single top-tube and pivoting-fork rear suspension.
Forks: hydraulically damped telescopic.

The first Ducati racing motorcycle was derived directly from production models. This was the 100 Gran Sport, which had a single-cylinder, four-stroke engine with overhead bevel gear distribution.
The Ducati 100 won a host of endurance and speed races. The next Ducati racer, the 125, did the same. Private racers rode it even in first-class and Grand Prix racing. And the Ducati sports motorcycle was constantly being modified for racing by private riders throughout the world. At this point the Ducati company felt indirectly forced into official racing. It started out with the Milan-Taranto race and the Tour and then went into world championship racing with its small motorcycles.

The moment for entering racing
came in 1956, the year Fabio Tag-lioni, the Ducati designer, tried to transform a 125 Gran Sport with his own distribution system, which was not altogether original. Taglioni had been working on it for years, but the system had never been applied in practice because of the difficulties he had encountered in tuning.

Taglioni's distribution system involved "desmodromic" valve control, which made it possible to mechanically control the movement of the valve without having to rely on the variable elasticity of the springs, a source of difficulty with production models and racing models alike.

The Ducati 125 "desmodromic" Grand Prix racer made its debut in 1956, when it went into Grand Prix racing. Degli Antoni rode the small motorcycle to win that year's Swedish Grand Prix.
In 1957 the Ducati 125 was given an improved engine. Streamlined fairing was installed, but without success. Although the Ducati was technically more advanced than the MV Agusta and Mondial of the same class, it was not more powerful. The Ducati gave a better ride because of its better use of the engine.

This feature was the Ducati's ace in the hole in 1958 when new regulations abolished overall fairing, causing MV and Mondial to lose precious speed. As a result the distance between the Ducati and those vehicles was reduced. Now the Ducati's reliable performance and fine chassis proved their worth.

There were several Ducatis in the 1958 world championship. The Belgian and Swedish Grand Prix went to Ducati, as well as places of honor in Holland and at the Isle of Man Tourist Trophy. At the Italian Grand Prix the 125 took the first five places, with Spaggiari, Gandossi, Villa (who rode the 125 two-cylinder "desmodromic" in its first race), Chadwick, and Taveri.
 


Motorcycle: Ducati 125 "Desmodromic" Manufacturer: Ducati Meccanica, Borgo
Panigale, Bologna Type: Racing Year: 1958
Engine: Ducati single-cylinder, four-stroke, "desmodromic" distribution with three overhead camshafts, bevel gear shaft. Displacement 124.8 cc. (55.3 mm. x 52 mm.)
Cooling: Air
Transmission: Five- or six-speed block
Power: 19.6 h.p. at 13,800 r.p.m.
Maximum speed: About 115 m.p.h.
Chassis: Double cradle, continuous, tubular. Front and rear, telescopic suspension
Brakes: Front, central drum, four shoes; rear, central drum