Ducati Scrambler History

3 Feb 2015 | Author: | Comments Off on Ducati Scrambler History
Ducati 125 Scrambler

125/250/350/450 Scrambler

The first production versions of the wide-case engine appeared in early 1968 as the 350 cc Scrambler, and in the US as the 350 Sport Scrambler. This was followed shortly afterwards by the 250 Scrambler. The Scrambler was to become the most popular of all the wide-case singles, particularly in Italy.

It offered full street equipment, with no pretensions for off-road ‘ competition as had been evident in the prototype 350 Scrambler of 1967, and the 250, 350, and even the later 450 versions, were essentially similar.

This 350 cc wide-case engine shared the same dimensions of 76 x 75 mm with the 350 Sebring and Mach 1/S racer, and had a 10:1 compression ratio and a high performance camshaft (coded white/green). This had valve timing figures of inlet opening 70º before top dead centre and closing 84º after bottom dead centre, and the exhaust valve opening 80º before bottom dead centre and closing 64º after top dead centre.

They certainly required the decompression lever operated from the left handlebar. The 250 had a 9.2:1 compression ratio and no compression release. Using 35 mm Marzocchi forks, the 1968 versions of the 250 and 350SCR had their Veglia speedometer mounted in the Aprilia headlight. They came with 315 mm Marzocchi shock absorbers, later replaced by 310 mm items, with the option of stiffer suspension available.

Very soon after they were released they were restyled, with a new petrol tank and seat design that would carry through uncs 19′ 4. ‘The 350 then became the 350SSS (or Stteet. Scrambler Sport) for the US market.

In 1969 the 450 (actually 435.7 cc) became available, and featured a new crankcase, cylinder, and cylinder head castings to accommodate the 86 x 75 mm dimensions. The reason why a full 500 wasn’t created was that the 75 mm stroke was the largest that could be used for the throw of the crankshaft to miss the gearbox pinions. To make the engine larger would have required a redesign and retool.

Interestingly enough, even though the 450 shared the 75 mm stroke with the 350, the 450 used a con-rod with an eye-to-eye length of 140 mm, rather than the 136 mm con-rod that was used by both the 250 and 350. Certainly with a rod length to stroke ratio of 1.81:1, the shorter rod was not ideal for the longer stroke 350, accentuating piston acceleration.

For the 450 there was also extra gusseting along the top frame tube, exactly like Spaggiari’s 1968 450 racer, and a wider chain and sprock-ets, allowing the use of a 5/8 x 3/8 inch final drive chain. With a 9.3:1 compression ratio, and white coded camshafts of the 250SCR, the 450SCR (and identical Mark 3) produced a moderate 27 bhp at 6,500 rpm.

Ducati 125 Scrambler

The valve timing was inlet opening 27º before top dead centre, closing 75º after bottom dead centre, and exhaust opemng 60º before bonom AeaA centre, anA cos’ing 3lº after top dead centre. 1n 1969 the US model of the 450 Scrambler was marketed by Berliner as the Jupiter. With the 450 came slightly longer (515 mm) Marzocchi forks, and these were also fitted to subsequent 250 and 350SCRs.

All the carburettors were changed during 1969, with the Dell’Orto SS1 29D being replaced by a new square-slide VHB. The 250 received a smaller VHB 26AD (from 27 mm), and the 350 and 450, a VHB 29AD. This required a new air filter and the traditional rounded muffler became the cut-off Silentium type, either long or short. At the start of 1970 the crankpin diameter was increased to 30 mm, and the Scramblers then

remained unchanged until 1973, when they became very similar to the range of Mark 3 roadsters. They now had Borrani 19-inch and 18-inch alloy wheel-rims, and the 350 and 450SCR the same double-sided front brake, headlight, and instruments as the Mark 3. They also featured Marzocchi forks with exposed staun-chions and new side-covers. The 250 still had the single brake and fork gaiters (though US versions differed), and all now went back to using the older rounded muffler.

In 1973 they received the Ducati Elettrotecnica electronic ignition, and finally a larger, 32 mm diameter crankpin in 1974.

For a short while during 1971 a 125SCR was actually built in Bologna with a narrow-case Spanish Mototrans five-speed engine, complete with Spanish Amal carbu-rettor. This wasn’t a success and was soon discontinued, but the final 250 Scramblers of 1974 also used Spanish-built engines.

Ducati 125 Scrambler
Ducati 125 Scrambler

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