DKW250
Classic Bikes DKW250 | |
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Overview[edit | edit source]
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 absorberwas
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
modelthe 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 chamberand 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 handlingbut 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 click
External Links[edit | edit source]
http://www.odd-bike.com/2014/02/dkw-supercharged-two-strokes-force-fed.html