DUCATI 750 S
Article #4, 9 April by Harné Heuvelman
Fabio Taglioni had combined two bevel drive single cylinders on a common crank-shaft which led to the first, nowadays so characteristic, Ducati trademark: the L-twin. The first prototype was tested in July. And with success, because only sixty days later the first Ducati 750 GT struck the Italian press like thunder.
The 750 GT’s introduction was a great success for the company and it was clear all along that a sporting version of the touring bike was on its way. Development began in 1971 and the new bike was ready for introduction in 1972: the Ducati 750 Sport.
Although the bike was officially called the 750 Sport, it became also known as the 750 S and later on as the ‘yellow sport’, referring to the colour and perhaps to distinguish this model from the ‘green frame’ 750 Super Sport or 750 SS.
Anyway, the first examples of 1972 took the 750 GT as a basis and had the same wide rear sub frame. The leading axle Marzocchi front fork was similar but with black painted fork legs and the bike was fitted with a single Lockheed brake system, although this was replaced very soon in 1972 with a Scarab brake system. The 750 S was fitted with clip-on handlebars and rear-set foot pegs. This early model had a very distinctive black Z-shape stripe on the newly designed fiberglass yellow fuel tank and later became known as the Z-stripe version of the 750 Sport.
For the engine, the 750 GT was also taken as a starting point, only it had black painted covers, a lighter crankshaft, high compression pistons and larger Dell’Orto 32mm carburetors (Amal carburetors were never fitted on the 750 S unlike on the 750 GT). Power output increased considerably because of the changes, up to 62 bhp at 8,200 rpm.
The 750 Sport was updated in 1973 with a narrower rear sub frame with ‘outboard’ mounted rear shock absorbers. The fiberglass fuel tank was narrower to fit the new frame and was finished with a black stripe in the centre and two smaller ones on the side with the Ducati logo. Side covers and seat were now only yellow. Scarab brakes were still fitted like on the ’72 model and also the engine was not changed, keeping its black covers.
1974 was the last official production year of the ‘round case’ 750 L-twin engine, a common name given to this engine type to distinguish it from the later ‘square case’ design, first introduced on the 860 GT in 1974 also. Updates on the 750 Sport included new camshafts and polished rather than black painted outer engine covers. The fuel tank was now steel instead of fibreglass and although some ’74 bikes were fitted with a centre axle Marzocchi front fork and Scarab front brake, most featured a centre axle Ceriani front fork and Brembo brake system.
The Ducati 750 S is one of the all-time great Ducati’s offering spectacular handling as was demonstrated by Paul Smart and Bruno Spaggiari’s 1972 Imola racing results on their stock-based machines. The round case engine and the sporty design features make the 750 Sport a very handsome bike; the best Ducati has to offer.
The 750 S ‘round case’ engine has vertically split aluminium crankcases, a 90 degree L-twin layout with the vertical cylinder inclined at 15 degrees upwards. The five-speed gearbox is incorporated in the engine crankcase and all 750 Sports have a right side gearshift. The valves are actuated by single overhead camshafts driven by a set of bevel gears and uses valve springs for closing (non-desmo). All 750 Sports are fitted with Dell’Orto PHF32A carburetors. Compared to the 750 GT, the 750 S has a lighter crankshaft and higher compression pistons. Engine covers were painted black in 1972 and 1973 but polished in 1974. The ’74 engine has updated camshafts.
The 1972 Z-stripe 750 Sport frame was largely the same as the 1972 750 GT and incorporated some of the basics of the earlier ‘wide case’ single frame. With its tubular steel frame, that uses the engine as a stressed member, the 750 S earned a reputation to be one of the best handling bikes available. The 1973 and ‘74 models had a narrower rear sub frame and had the rear shocks mounted outside the frame rather than under it.
1972 and ‘73 models were fitted with a leading axle Marzocchi front fork with black painted fork legs. Only a few early models featured a Lockheed brake system, very soon to be replaced by a Scarab brake system. All 1974 750 Sports have a centre axle front fork, mostly Ceriani although some were also fitted with Marzocchi (still with centre axle). Ceriani versions were fitted with a Brembo brake system, Marzocchi version with Scarab.
References (recommended further reading)
Falloon, Ian (2004) ‘ Standard Catalog of Ducati Motorcycles’, Iola: KP Books
Falloon, Ian (2006) ‘The Ducati 750 Bible’, Dorchester; Veloce Publishing
Falloon, Ian (1998) ‘Ducati Twins Restoration Guide, Bevel Drive 1971 – 1985’, Osceola; MBI Publishing Company