The Ducati Single Story

All Ducati bevel-gear overhead-cam singles can trace their lineage back to the Fabio Taglioni designed Gran Sport of 1955. Taglioni arrived at Ducati in 1954 after studying under Alfonso Drusiani at Mondial, and already with one very successful design to his name: the 75cc OHC Ceccato engine. His first design for Ducati, the 98cc Gran Sport, nicknamed "Marianna," used a bevel-drive single overhead cam and valves closed by hairpin springs. With superior performance and (just as important) rugged reliability, the Gran Sport won the 100cc class of the Milano-Taranto race for four successive years, from 1955 until the class was scrapped after 1958. Mariannas similarly dominated the Giro d’Italia, taking the first 12 places in the final 1957 race.

Having established its credentials in road racing, Ducati aimed its sights at Grand Prix. Taglioni’s first design, a 125cc DOHC  single proved reliable but underpowered. The engine needed more revs, but valve float and valve-to-piston interference problems prevented that: until, that is, Taglioni tried desmodromic valve operation.

Desmo wasn’t a new idea. In fact, numerous motorcycle innovators including James L. Norton, John A. Prestwich (JAP), Bert Hopwood and Richard Kuchen all had their names on desmodromic patents. Mercedes had also used it successfully in their 1954 W196 racer. But Taglioni was the only motorcycle designer to make desmo valve operation work in production.

Why desmodromic? Metallurgy has frequently lagged behind motorcycle engine development, and such was the case with valve springs. The heat generated in the cylinder head of a 1950’s air-cooled racing motorcycle engine was sufficient to anneal the steels then used for valve springs, weakening them. This led to valve float or bounce, so designers used external hairpin springs to prevent overheating. But a desmodromic arrangement closes the valves (usually aided by a light spring) as well as opening them. By preventing valve float, desmodromic valve operation means more aggressive cam profiles and higher engine revs can be used, both of which are usually needed for higher power output.

Taglioni’s genius was in developing a system that was both precise and reliable. His first desmo was essentially a "bialbero" (Italian for "twin cam") engine with a combined cylinder head/cambox containing two opening camshafts acting directly on the valves, with one central camshaft closing the valves by means of rocker arms. The result was an engine that could be revved to 14,000rpm, where the "spring" engine produced its maximum power at 11,500rpm.

The road-going Ducati Desmo single

Though Ducati launched its range of  "narrow case" road-going Desmo singles for the 1957 season, all used a single overhead camshaft with valve operation by rockers and enclosed hairpin springs. The engine grew from 100cc to 125, 160, 200, 250 and finally 350cc variants, strengthened along the way, but all similar in design (much as BSA/Triumph was able to stretch the 150cc Terrier engine to 200, 250, 350, 441 and finally 500cc). Arguably the most successful of these was the 250 Mach 1.

By 1967, Taglioni had demonstrated the reliability of his desmodromic valve gear, and the company thought it safe to use it on sporting versions of its revamped "wide case" production singles. First came the 350 (street-oriented) Scrambler, followed by 250 and 450 versions. Pure street 250, 350 and 450s followed in Mark 3 (valve spring) and Mark 3D Desmo versions. The 450 established the effective capacity limit of the wide-case engine with a 75mm stroke (longer would have required a redesign to move the gearbox pinions further away) and 86mm bore for 436cc.

The Mark 3 range came in a dizzying variety of finishes, trim levels and cycle parts depending on the year and market. In the United States, the Mark 3 was typically offered with steel wheel rims, lower compression and a softer cam profile, while the Desmos featured alloy rims, sporting camshaft, tachometer, and in 1968, a twin-filler gas tank.

For 1971, two further variants appeared: the off-road styled R/T (better equipped for dirt than the Scrambler), and a new street bike: the Silver Shotgun. The desmo engine remained unchanged apart from a stronger main bearing, but the styling was strictly café racer: rearset foot controls, clip-on handlebars, fiberglass "monoposto" seat with bum stop, fiberglass gas tank, and cut-off front fender. Cycle upgrades included Borrani 18-inch alloy rims, Grimeca double-sided, single-leading-shoe front brake with air scoops, and 35mm Marzocchi forks (replacing 31.5mm Ducati items). Apparent concerns about the safety of the fiberglass tank led to an eventual ban in the United States and the following year’s makeover by Italjet’s Leopoldo Tartarini.

The final Desmos appeared in 1973 with a steel gas tank, 35mm Ceriani forks, a 280mm Brembo disc brake, paired Smith’s clocks, and a CEV headlight. Tartarini’s remake also included a new orange-and-black color scheme to match the 1973 750 Sport.

Rubber meets road

The Ducati Silver Shotgun came into Fritz’s life by a pair of mistakes. In the late 1980s, Fritz acquired a Ducati Paso, the fully-faired, first generation belt-drive-cam sportbike. "I didn’t like the Paso much," he says. It wasn’t my kind of bike. I want to see the engine."

A local friend had also made a purchase he regretted: the Silver Shotgun. It wasn’t his kind of bike, either. "He wanted the Paso," says Fritz, " so we made a trade. I found out about the significance of it later on."

Very few Silver Shotguns were made. Though intended for the U.S. market, few were imported before the ban on fiberglass gas tanks. A dealer dispute at about the same time also restricted distribution, though some found their way to Canada. Fritz’s bike was sold through then Edmonton dealer Carters.

Fritz tells me his Silver Shotgun is essentially stock, though as a former machinist he’s improved on some parts, making new engine plates and brake torque arms. He’s also repainted the frame in the same sea green used on the 750SS, with the effect that his Shotgun looks like a mini-Imola bike.

More used to the mellow boom of a British single of the same size, I’m surprised at how restrained the 450 sounds when it fires up: there’s little mechanical noise, and the exhaust note is a polite brap-p-p-p-p-p. Fritz motors up and down the street while I take photos, making little more noise than a power mower — though a far sweeter sound.

There’s much to be said for the then-Italian philosophy of making a small motorcycle, then stretching and tuning the engine for more power. The result is a 450 that could run with much bigger bikes at the time: Italian magazine Motociclismo recorded a top speed over 98mph in a 1972 test. Slender, compact and lightweight, the 450cc Silver Shotgun may speak softly — but packs pretty big performance. MC