DUCATI WIDE CASE SINGLES
Article #2, 1 April by Harné Heuvelman
The final ‘narrow case’ to be entirely build in Bologna 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.
The name ‘wide case’ has only become popular to distinguish this type from the previous ‘narrow case’ models. The largest difference between the two being that the latter type had narrower frame mountings on the crankcases to fit in an earlier frame design.
As is often the case with new Ducati designs, the new ‘wide case’ single was born on the race track. In 1967, Ducati introduced the 250 and 350 Sport Corsa Desmo (SCD) incorporating the new crankcase design. This first saw its way to the road with the 1967 350 Scrambler and a year later with the 250 Scrambler. Although more street oriented than the ‘off-road look’ would suggest, the Scramblers were very popular in Europe and in the US and remained in production until 1975. Some minor updates included a new fuel tank and seat design in 1968 and a different ‘angle-cut’ Silentium exhaust muffler in 1970. This year, with the introduction of the 450 Scrambler, the Dell’Orto SS carburetor was replaced by VHB types of the same manufacturer. From 1973 on all Scramblers where fitted with Borrani aluminium wheels.
With the introduction of the 450 Scrambler in 1969, the largest possible engine displacement of the Ducati bevel drive singles was reached, as engine stroke was limited to 75mm. The 450 Scrambler had a strengthened frame compared to its 250 and 350 sisters to cope with the extra power.
While the ‘narrow case’ 250 Diana Mark 3 was still available in the US in 1968, the European market saw the introduction of the ‘wide case’ 250 and 350 Mark 3. The engine specification was virtually unchanged compared to the narrow case models. Unique for the 250 and 350 Mark 3 of 1968 are the twin filler caps on the fuel tank, later models had a single filler cap (as was the same with the Mark 3 Desmo). The model was further updated in 1973 with a new fuel tank, seat and side covers, Marzocchi front fork and Borrani aluminium wheels. In 1974 a 239 Mark 3 was introduced for the French market as taxation on motorcycles larger than 240cc was legislated.
Desmodromic valve actuation uses a closing rocker instead of valve springs and was a feature on many Ducati racing bikes. Fabio Taglioni and Ducati spent much effort on developing this technique since racing introduction on the Ducati 250 and 350 SCD as it has a big advantage over conventional valve springs; especially in high revs, the valve actuation stays much more precise and prevents valve float.
Ducati’s first street model to feature this high-tech desmodromic valve actuation was the 250 and 350 Mark 3 Desmo of 1968. Although apart from the Desmo camshaft the engine and chassis was identical to the non-desmo Mark 3 (only a letter ‘D’ on the side covers and chrome fenders set it apart), this became one of the most desirable single Ducati’s. The ‘Desmo’ first came with Dell’Orto SS1 carburetors also replaced in 1970 with Dell’Orto VHB.
In 1969, with the 450 Srambler, the Mark 3 range was expanded with the 450 Mark 3 and the 450 Mark 3 Desmo all fitted with a 29mm Dell’Orto VHB carburetor from the introduction. The chassis and styling was identical to other Mark 3 family members and was updated in 1971 with a larger and rounder fuel tank
The Scrambler range was more a dual purpose road bike, but with the introduction of the 450 R/T in 1971, Ducati offered a true dirt bike. Designed with the help of Italian off-road champion Walter Reggioli, the 450 R/T shared the engine specifications with the 450 Desmo but with polished valve rockers, a compression release, a flywheel magneto (no battery) and, on US versions, a high rise exhaust pipe. The chassis was completely new and specifically designed for this model and featured a Marzocchi fork and a fibreglass fuel tank. In 1974 a 350 R/T was introduced for the Italian market only.
In 1971, the Mark 3 range transformed into the 250 Desmo, 350 Desmo and 450 Desmo with the Scrambler range still available. The new models where much sportier than before and all featured ‘café racer’ style clip-on handlebars and ‘monoposto’ single seat. The non-desmo engines where discontinued and specifications of the Mark 3 Desmo’s where taken as the basis for the new range.
In 1973 the colour scheme was adapted to that of the 750 S; yellow and black. The fuel tank now was made of steel and the bike featured restyled side covers and a seat with incorporated fender. In 1974 a few 239 Desmo’s where manufactured, again for the French market only.
The final production of the Ducati bevel single took place in 1974 with the 250, 350 and 450 Desmo’s now fitted with a Ceriani front fork and a single Brembo disk brake. Although a handful of singles where again built in 1978, the Ducati single would only come back to life with the Supermono in 1993, to die again in 1995. This time for good?
All Ducati ‘wide 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 straight cut bevel gears from the crankshaft. The five speed gearbox is integrated in the crankcase. The Mark 3 Desmo’s as well as the later 250, 350 and 450 Desmo’s and the 350 and 450 R/T are the only ‘street’ singles to be fitted with desmodromic camshafts. Until 1969, most singles where fitted with a Dell’Orto SS1 carburetor, after 1969 with a Dell’Orto VHB. Power output ranged from 19 bhp with the 250 Scrambler up to 36 bhp with the 450 R/T.
All wide case singles have a single-down tube tubular steel frame, utilised as a stressed member. The engine is mounted using two plates at the front and directly at the rear. Most models have a 35mm telescopic Marzocchi front fork apart from most Mark 3 models (until 1973) which had 31.5mm Ducati forks. 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