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Ducati 125 Desmo

(by Ian Falloon, Oct 2022)

Ducati 125 desmo


Pioneering two-pot screamer

The first indication that Ducati were interested in building larger, multi-cylindered motorcycles came at the Milan Show in December 1956, with the unveiling of a 175cc double overhead camshaft parallel twin with exposed valve springs.

This was raced in the final, 1957, Giro d’Italia by Leopoldo Tartarini, but it retired in the 3rd stage. Dating from drawings first sketched by Taglioni in 1950, it was an interesting, if complicated design, with the pressed up crankshaft consisting of two flywheel assemblies clamped by Hirth (radially serrated) couplings.

A jackshaft was driven off the middle of the crankshaft and this drove the twin overhead camshafts by a train of spur gears. While the 49 x 46.6mm 175 produced considerably more power than the 175cc single cylinder Gran Sport at 22 bhp at 11,000rpm, the narrower power band and increase in weight to 112kg (247 lb) largely negated this benefit.

The 175 became the basis for a 125cc Grand Prix machine first raced by Franco Villa at the Italian Grand Prix at Monza in 1958 where it finished third in that remarkable Ducati 1-5 clean sweep.

This 125 was intended to replace the single by producing more horsepower through increased revs, and the 42.5 x 45mm engine produced 22.5 bhp at 13,800rpm. A similar three camshaft desmodromic valve system to the single allowed the engine to rev to an amazing (for the time) 17,000 rpm, but the power band was extremely narrow and the bike difficult to ride despite having a six-speed gearbox.

As with the 175 twin, the 125 was also too heavy at a claimed 92kg (203 lb), and the handling was less than satisfactory. Compared with the single, the twin (of which only three were built) didn’t achieve much success. Breakages in the camshaft drive gear train often occurred, with disastrous results, and the bikes were sold at the end of the 1959 season, two of which ended up being raced by Mike Hailwood.

It was during 1959 that Stan Hailwood commissioned a 250cc version for Mike to race in 1960. Revealed to the press in February 1960, the 250 shared the same 55.25 x 52mm dimensions with the 125cc single, but in other respects was a scaled up 125 twin. The power was 43bhp at 11,600rpm, and it was a very fast motorcycle with a top speed in the region of 218 km/h (135 mph), but it handled poorly and was considerably overweight.

At about the same time, Ken Kavanagh, about to undertake his successful series in Australia, persuaded the factory to build a 350cc desmo twin for the 1960 season. This appeared in time for Kavanagh to race at Imola in April but an accident prevented him from riding it until the Isle of Man, by which time Hailwood also had a similar machine.

With a bore and stroke of 64 x 54mm, the 350 produced 48bhp, but the engines vibrated badly and the bikes needed a lot of development to be competitive. At the end of the season John Surtees bought both Hailwood’s 250 and 350, followed a few months later by Kavanagh’s.

They received new frames and leading-link forks by Ken Sprayson and Phil Read rode a 350 at the Isle of Man in 1962 where it blew up in practice. They were raced unsuccessfully for a couple more domestic British seasons.

There was however to be one more multi-cylindered disaster. Seeing the limitations of a single, or even twin, at Grand Prix level, Taglioni designed a 125cc in-line four cylinder engine in 1958. This idea was advanced for the time but with Ducati’s withdrawal from competition at the end of 1959, the design languished until the Spanish Mototrans concern persuaded Ducati to produce it five years later, in 1964, by which time it was obsolete in a few design areas.

There were four non-desmo valves per cylinder and a very wide 90 degree included valve angle. The double overhead camshaft 125 used a train of gears on the left side of the engine to drive the camshafts. With a compression ratio of 12:1 and four 12mm Dell’Orto carburettors, the 34.5 x 34mm engine produced 23bhp at 14,000 rpm, hardly outstanding considering that the 125cc twin had produced 22.5bhp in 1958.

Even with twelve months of development the power was only increased to 24 bhp at 16,000 rpm, and Ducati realised that it would never be competitive at Grand Prix level. Only two bikes were built and during 1966 the 125 four quietly disappeared.

The entire parallel twin and four cylinder episode was interesting in that they were the first Ducatis designed exclusively for racing bearing no relationship to any road bikes.

Because they were so unsuccessful compared to the Gran Sport derivatives none of their features ended up on the production line, but they certainly had the effect of creating a Taglioni philosophy that would prevail in the future. That of producing a motorcycle with a balance of power and weight.

There was no point in an unnecessarily complex and heavy motorcycle if this did not translate into improved lap times. Also, what good was a powerful motorcycle if it did not handle well or the powerband so narrow that it was unride-able?

Not only was it significant that the desmodromic Grand Prix racer was closely derived from a road bike (albeit a catalogued racer with lights), but all future Ducati success would emphasise a broad range, rather than outright power, and a balance b
etween power and weight


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