DKW  SS 350 Three Cylinder




DKW SS 350 1953

HREE-CYLINDER DkW. Possibly the only three-cylinder machine to have been raced in the I.o.M. T.T. events since they began 'way back in 1907, the 1953 German 350 c.c. D.K.W. design was not destined to achieve distinction in that series for, after one rider had had an accident during practice week—though not in a practice period—the other, Siegfried Wiinsche, retired at Ramsey on the second lap of the Junior T.T. after lying about fifteenth on lap 1.

The machine did, however, achieve some degree of success on the Continent and became almost legendary for its fantastic rate of acceleration.
This feature came about not only because of an excellent power output, but because the machine had been designed from the start, by Ing. Wolf, as a lightweight. Light alloy was used for almost everything and the factory had a set of four interchangeable tanks made, in capacities from 2 to 7 gallons, for each machine, so that weight could be saved according to race length. This policy paid off, for the dry weight of the complete machine was a mere 180 lb.!

Weight is the start of a vicious circle in design—if a machine is heavy it needs more powerful (and so, generally, heavier) brakes to stop it— which puts the weight up further. The better brakes need stiffer forks to cope with the increased load . . .

But what of the power unit, with its triple crankcase in unit with a four-speed box? Each light-alloy barrel, with cast-in liner, and its head, with hemispherical combustion chamber and central plug, was held to the crankcase by four through-bolts. Although the factory's 250 c.c. twins employed a rotary inlet valve, the "350" had a normal—more or less—three-port inlet, transfer and exhaust system. The outer cylinders were parallel, but the centre one lay horizontal (6o° from the others) and a 120°, three-throw crankshaft was used, running in five roller bearings.
Each crank compartment was, of course, sealed from its neighbours.

One float chamber was shared by the 28 mm. bore carburetters for "rear" pots and, to cope with the unit's 12,000 r.p.m., a six-cylinder Bosch magneto was used, running at half engine speed and driven by bevels from the offside crankshaft end.

Engine: three-cylinder 350 c.c. two-stroke with 1200 firing intervals; light-alloy barrels with cast-in liners; claimed maximum r.p.m. 12,000.
Ignition: six-cylinder Bosch magneto driven at half engine speed by bevel gears.
Transmission: four-speed gearbox in unit with engine, chain final drive.
Frame: ultra-light duplex cradle with swinging-fork rear suspension.
Forks: telescopic.

DKW SS 350 Three-cylinder 1955

Though World War II brought a lot of changes everywhere, the designers at DkW persisted in maintaining the racing possibilities of the two-stroke engine. After the war Zschopau in Saxony became part of East Germany and DkW relocated in Ingolstadt, where it went back into motorcycle manufacturing. Two new designers, Wolf and Jacob, succeeded Zoller at DkW, but they shared his general views.

Wolf and Jacob built a new two-stroke engine with three cylinders arranged in V form. Two cylinders were parallel and slightly tipped forward. The cylinder between them was horizontal.
The engine was quite different from
the older supercharged models. But if one looked at the cylinder pump of the URe, in effect a kind of atrophied engine cylinder, one might argue that the URe also had a three-cylinder V engine, aside from the fact that the upper two cylinders, although parallel, were set longitudinally.

The new two-wheeler made its debut at the 1952 Swiss Grand Prix, but the DkW 350 three-cylinder did not look as promising as its predecessors. All it had in common with them was the large fuel tank, which gave it a very heavy look.

Throughout 1953 and 1954 the DkW 350 never started a race as a favorite. The 350's lack of success only spurred the DkW designers to try harder. Late in 1954 the three-cylinder vehicle was generating 42 h.p. in tests, a record for its displacement.
To compensate for the almost total lack of engine-braking (due to the two-stroke cycle), the designers gave this DkW a new suspension system and a large front and rear brake.

The chassis was extensively modified and the cylinder exhaust system was redesigned. Thus appeared the first expansion chambers, which are now standard on all two-cylinder racing motorcycles.

In 1956 the DkW 350 seemed really competitive; indeed, it was faster and more powerful than the competition. The DkW's rivals that year were the Italian four-cylinder Gilera and the Moto Guzzi single-cylinder. Although the Guzzi was less powerful than the DkW, it was also considerably lighter in weight than its German rival.
The DkW showed its unusually high speed when it won at Hockenheim, the fastest circuit in Europe. Subsequently it had disappointing losses, and late in 1956 it was withdrawn from racing.

Motorcycle: DkW 350 Three-cylinder Manufacturer: Auto Union DkW, Ingolstadt Type: Racing Year: 1955
Engine: DkW three-cylinder, two-stroke, V (two vertical cylinders and one horizontal cylinder) with cross-port distribution. Displacement 349.4 cc. (53 mm. x 52.8 mm.)
Cooling: Air
Transmission: Five-speed block
Power: Over 42 h.p. at 10,500 r.p.m.
Maximum speed: 130 m.p.h.
Chassis: Continuous double cradle with tubular elements. Front, swinging-trigger suspension; rear, telescopic shock absorbers
Brakes: Front, central drum with four hydraulic shoes; rear, central drum with hydraulic controls and supplementary hand control

For a complete DKW racing history