DUCATI 860 GT / GTE / GTS
Article #6, 10 April by Harné Heuvelman
Although the ‘round case’ 750cc engine of the 750 GT and 750 Sport was a great engine, offering very good and smooth power output, it had its problems. It was highly complicated and therefore expensive to build, noise reduction of the internal motor parts was needed to comply with regulations and a left side gear-shift was needed for the US market.
Back to the drawing board! Fabio Taglioni went to develop a simpler bevel gear configuration and Giorgetto Giugiaro of Studio Italdesign was given the assignment to design a successor for the 750 GT with a matching engine. The result was the first ‘square case’ bevel twin: the 860 GT, introduced in 1974.
The engine got the newly ‘Ital’ designed outer engine covers and a bevel gear layout using an extra plate for setup. The con-rods were shortened and larger Dell’Orto 32mm carburetors were fitted. The gearshift moved to the left with a crossover rod behind the engine. A starter motor was fitted on the 860 GTE (E for electric start) a model following the introduction of the 860 GT (without starter motor) shortly. The new model came with Lafranconi exhaust mufflers to meet noise regulations.
The frame was a completely new development as well, with an increased steering angle and kinked front down tubes. The 860 GT received an ‘angular’ design with an almost ‘square’ steel fuel tank. A Ceriani front fork was fitted with a single Brembo disc and chrome plated steel rims.
The 860 GT and 860 GTE did not prove to be the success Ducati had hoped for. Instead the bike was seemed to be ugly and in many respects a step back from the great 750 GT it was replacing. Sales were bad in ’74 and ’75 and the factory responded with the introduction of the 860 GTS in 1976.
The 860 GTS had an electric starter motor as standard, Smiths instruments and a Marzocchi front fork with duel Brembo disc brakes fitted. The fuel tank was restyled to make it more ‘curved’ but the improvement may have been too small. Sales dropped even further with the 860 GTS in ’76 and ’77.
With the introduction of the 900 SD ‘Darmah’ the 860 GTS became the 900 GTS and received the same engine updates with an improved left side gear-shift and Bosch ignition. In 1979 the model was discontinued.
On the one hand, the Ducati 860 GT meant a lot for Ducati as it was the first to be fitted with the new ‘square case’ bevel L-twin. This engine played in important role for Ducati during the seventies and early eighties in the 900 SS, Darmah and Mike Hailwood Replica.
On the other hand the 860 GT(E)/GTS was a big misconception. The design was a failure as it still struggles to find a place in hearts and souls of classic Ducati enthusiasts. Sales were never on the forecasted level and the model died a slow death in 1979 when only 150 were produced.
Ducati learned from the 860 GT failure, shown by the introduction of the 900 SD Darmah in 1977. Although the two models were available simultaneously, the Darmah is regarded as the better sporty touring bike of the two which is also reflected by the sales number of 1977 and 1978.
The 863cc ‘square case’ L-twin was a novelty on the 860 GT and formed the basis for all other ‘square case’ models introduced later on. Although technically based on the 750 ‘round case’ L-twin, this engine had a lot of improvements for faster and simpler assembly. The outer engine cases were designed by Giorgetto Guigiaro of Studio Italdesign. Cylinder head design was based on the 750 GT with the same valves in identical sizes, actuated by single overhead camshafts driven by a set of bevel gears and uses valve springs for closing (non-desmo). The 860 GTE and 860 GTS were fitted with an electric starter motor. All 860 GT’s and GTS’s have Dell’Orto PHF32A carburetors. The engine was updated in 1978 with the introduction of the Darmah, and although it was called the 900 GTS now, the engine displacement was still 863cc.
The frame was specifically designed for the 860 GT and featured an eccentric pivot chain adjusters and kinked front down tubes, flattened at the end. The front fork was Ceriani until 1978 when it was replaced by a Marzocchi together with the upgraded dual Brembo disc brakes.
References (recommended further reading)
Falloon, Ian (2004) ‘Standard Catalog of Ducati Motorcycles’, Iola: KP Books
Falloon, Ian (2008) ‘The Ducati Bible: 860, 900 & Mille All models 1975 to 1986’, Dorchester; Veloce Publishing
Falloon, Ian (1998) ‘Ducati Twins Restoration Guide, Bevel Drive 1971 – 1985’, Osceola; MBI Publishing Company