DKW 250

 

 

 

DKW URe 250 1937

After the happy but short career of the Garelli motorcycle in the early 1920s, no other motorcycle manufacturer (except for Scott in England, which raced only locally) tried to match a two-stroke engine against the most famous British and Italian four-stroke engines.
The DkW company of Zschopau, however, had great faith in mixture-fed engines. For years the company had been producing motorcycles with two-stroke engines in various displacements. The DkW two-strokes, used mainly in minor races, stood up well against their competitors' finely tuned four-stroke engines.
In 1928 a two-stroke, single-cylinder DkW 175 with supercharger won in its class at the Italian Grand Prix. The motorcycle, ridden by Geiss, generated 11 h.p. at 5,000 r.p.m., putting it at least on a par with Tonino Benelli's unbeatable Benelli 175.
Three years later Zoller, the DkW designer and racing manager, set out to prove that the two-stroke engine was just as good as any other kind. In order to make his idea a reality he followed two paths: He organized the most impressive racing team that had been seen in Europe, and he built a brand-new engine that was revolutionary in being a two-stroke two-cylinder with supercharging by means of a cylinder pump.

The Zoller engine had two cylinders that were joined by a single combustion chamber. There were two pistons with a single piston pin. The main connecting rod was that of the rear cylinder; the other, smaller one was linked to the main one and worked on the same coupling axis. The motorcycle was fairly old-fashioned and heavy in appearance. The prototype had a rigid chassis with front-wheel elastic suspension. After 1935 a rear-wheel guide suspension —with vertical sliding pivot and spring and a hydraulic shock absorber—was added.
This was the URe. The German motorcycle raced with varying success between 1935 and 1937. The DkW racing unit, consisting of some 100 people, always arrived early at the track to handle every detail of the race. Each racer had three motorcycles at his disposal as well as a certain number of mechanics.
The DkW URe 250 also won many races run by private racers. After it had confirmed Zoller's theories about the viability of the two-stroke engine, DkW replaced the URe in 1938 with the new model ULd.

Motorcycle: DkW URe 250 Manufacturer: DkW, Zschopau Type: Racing Year: 1937
Engine: DkW two-cylinder with two-stroke cycle and horizontal cylinder pump supercharger, gill air intake. Displacement 123.5 + 124.9 = 248.4 cc. (47.5 mm. X 69.7 mm. and 47.5 mm. X 70.5 mm.)
Cooling: Water
Transmission: Four-speed separate
Power: About 30 h.p. at 5,000 r.p.m.
Maximum speed: Over 105 m.p.h.
Chassis: Continuous double cradle in tubular elements. Front and rear, elastic suspension
Brakes: Front and rear, central drum

DKW ULd 250 1939

After his success with the DkW URe, designer Zoller further improved his two-stroke, double-cylinder engine in 1938.
The chassis part of the motorcycle remained almost the same when DkW put the new model—the ULd 250— into the field. The engine, however, was considerably changed. In the URe the cylinder pump was horizontal at a 90° angle to the two engine cylinders. In the ULd the cylinder pump was mounted vertically at the front end of the engine. At the supercharger head of the new model there was a rotating valve served by two carburetors.
Serviced by ,the same large staff of men and equipment as the URe, the ULd won the 1938 Isle of Man Tourist Trophy at record speed. Because of its excellent acceleration and high speed, the rider Ewald Kluge was able to stop twice for fuel, while his adversaries could stop only once.

This compensated for the ULd's high-er-than-average fuel consumption. Kluge still managed to cross the finish line twelve minutes ahead of the second-place motorcycle.
Although the DkW ULd 250 used more fuel than any other comparable or larger motorcycle and tended to be unstable both in curves and on the straightaway, Kluge managed to ride it to the European championship in two consecutive years, 1938 and 1939.

A watercooled 250 c.c. two-stroke with three pistons, a rotary valve and only one sparking plug. That is part of the specification of the D.K.W. on which Ewald Kluge won the 1938 Lightweight T.T. by over ten minutes! In doing so he cracked round to raise the lap record almost 3 m.p.h. by clipping 57 sec. from it.

Basically his machine was virtually a split-single (like the Puch machines of post-war years) with watercooling and two rearward facing exhaust ports. A third piston, of considerably bigger diameter than the "working" pair, was fitted in a pumping cylinder that lay horizontally in line with the machine, forward of the crankcase. Above this, and forward of the watercooled block, was mounted a transverse rotary valve that had an Amal carburetter at each end\ Mixture was taken from both carburetters through the rotary valve to the big cylinder which was only a pump. This rammed the mixture into the working chamber—and out through the exhaust ports at slow speeds.

The model quickly achieved fame for its fantastic noise, its fantastic speed and its fantastic petrol consumption. To cope with this last, unwanted, attribute it had a massive tank that enshrouded the header tank of the radiator.
Although first glimpse at the photograph suggests that it had plunger rear suspension, this is not so; the machine has a rear pivoting-fork with a pivot bearing on the seat pillar tube and the "plunger" units merely contain the springs.

Despite a full duplex cradle frame, and the rear suspension, the model had not got a very good reputation for handling—but its speed still made it a winner.

SPECIFICATION
Engine: watercooled split-single 250 c.c. two-stroke, with rotary inlet valve and supercharging pump cylinder.
Ignition: flywheel magneto.
Transmission: chain via four-speed gearbox.
Frame: duplex cradle with swinging-fork rear suspension controlled by "plunger-type" spring boxes.
Forks: single-spr'ng girder with friction damping.

For a complete DKW racing history clickd-bike.com