twin
cylinder
engine cutaway
Leading
link setup on the
MB range
1958 TT
Adler
"Sixdays"-
early frame model
|
Adler racer - built in 1994
Classic Bike - May 1988
"The Two Stroke Takes Off"
Adler
paved the way
for the modern stroker twin.
by Stefan
Knittel
(many thanks to Stefan Knittel for giving me permission to reproduce this article)
TWO of the best known names associated with the German motorcycle industry are still with us today, albeit on office machinery like typewriters and calculators. Triumph (TWN of Nuremberg) and Adler have concentrated on this type of product since 1957. Known as TA, they are now both part of the giant Volkswagen concern.
Both firms began as bicycle makers in the 1880s, and built their first motorcycles just after the turn of the century. The Adlerwerke, owned by Heinrich Kleyer, did very well during those early years. Having celebrated the manufacture of their 100,000th bicycle in 1898, Adler promptly began to produce the typewriters which still bear the Eagle (Adler, in German) logo today.
The first Adler cars appeared in 1900. They were powered by De Dion engines, rapidly superseded by units of Adler's own design. A smallish 2.5hp single with both valves side by side in the front of the cylinder block - and with the inlet opened automatically by suction - led to the start of the Adler motorcycle range.
By 1907 this early design had gone, and the eight models in that year's catalogue all featured the then-fashionable inlet-over- exhaust valve layout but still with an 'atmospheric' automatic inlet. There were 2.5hp and 3hp singles as well as 3hp and 4hp V-twins. Instead of the standard coil ignition, a more reliable Bosch magneto could be ordered as an extra.
Forecar attachments, a tradesman's box and even a spindly-looking sidecar sporting a wickerwork seat were advertised.
However, motorcycle sales dwindled rapidly. By the end of 1907 only NSU and Wanderer remained as motorcycle producers. Adler relied upon cars, bicycles and typewriters for the next 40 years.
The front wheel drive Adler Trumpf Junior was one of the most popular German cars of the 'thirties and modernised prototypes based upon the pre-war design appeared at the Hanover Export Fair in 1948. But with most of the Frankfurt factory's contents removed by the victorious Allies, Adler was in no position to restart production.
Typewriter production resumed, and Adler took over a profitable machine tool factory next door. When the Allied military government announced a 60cc capacity limit for all future German motorcycle designs, Hermann Friedrich, Adler's managing director and chief engineer, recognised the restriction as an interesting challenge. In these circumstances, having been away from motorcycle production for so long was a small handicap. Along with virtually every other German manufacturer, Adler was starting from scratch.
Friedrich ruled out a conventional motorised bicycle of the type built around 98cc Sachs and NSU engines, although these had sold in large numbers before the war. He envisaged a modern, powerful and reliable engine mounted in an up-to-date frame. It was to be both light and comfortable to ride.
A wooden mock-up was ready by the time the 60cc limit was eventually abandoned. The design had to be modified slightly, but in 1949 production of the Adler M100 started. Its 98cc two-stroke engine was fairly conventional, featuring Schnurle loop-scavenge porting and a power output of 3.7bhp at 4800rpm.
A three-speed gearbox complete with clutch, kickstart and footchange was bolted to the left hand side of the engine. So the whole unit was rather wide, but very short. A well-designed double cradle frame in small diameter tube housed the motor. There was plunger-type suspension at the rear and pressed-steel, leading-link forks at the front. These featured spiral clock springs and friction-disc dampers on either side of the wheel, an ingenious and unorthodox idea.
The Adler M100 sold well, but did not prove to be the sort of moneyspinner Friedrich had envisaged. The sensational NSU Fox - with its 5.7bhp 98cc ohv four-stroke engine and cantilevered swinging arm - was the main attraction in the lightweight market.
Adler
was forced to enlarge its range. When the Frankfurt motorcycle show opened
in October 1951 the company was able to display three new motorcycles.
The M125 was a bigger version of the 98cc model, with a power output of
5.5bhp. But the star of the Adler stand was
the M200:
the
first modern twin cylinder two-stroke.
Friedrich and his engine man Felix Dozekal had been quite well aware of the risks involved in breaking fresh ground. But they chose to ignore the obvious option of another single since DKW, Zundapp and others were already in production with similar designs. Whatever they produced would have to be different.
There was no question of just adding another cylinder to the M100. Its engine and gearbox layout was already wide enough. So a completely fresh design had to be laid out with the aid of Adler's machine-tool factory. It was Friedrich's aim to make most of the M200's component parts on his own machinery.
The major difficulty to be overcome in designing a successful two-stroke twin concerns crankcase sealing. Adler's solution was both ingenious and complicated. The two cranks had to be fiddled into each side of the one-piece crankcase casting, then their serrated joints were drawn together by means of a through-bolt.
A roller bearing and two sealing rings were located in the centre web of the crankcase. To tighten the through-bolt, a special splined tool was inserted through a hole in the right-hand flywheel to mate with a radial serration on the bolt head. The complete crank assembly was supported at each end in bearing housings fitted to the crankcase sidewalls.
Two separate cast-iron cylinder barrels were deeply spigoted into the case, inclined forward at 45 degrees and topped by well-finned alloy cylinder heads. The primary drive was by helical gears on the left side of the engine, but the clutch remained in an outrigger position on the left-hand end of the crankshaft. No longer a single-plate dry unit, the multi-plate clutch ran in the oil bath it shared with the primary drive gears.
A four-speed gear cluster was inserted into the rear compartment of the unit- construction engine, the final'drive sprocket taking power off on the right. The generator and coil ignition system - with twin contact breaker points - was mounted on the right, too. The single carburettor, at first a 19mm Fischer-Amal followed by a Bing instrument, was situated in an enclosure above the gearbox.
This very compact, egg-shaped unit was put into a heavier version of the Adler duplex frame. The front forks still featured clock spring suspension, but the plungers were redesigned with the addition of hydraulic damping. Sixteen-inch wheels were fitted to promote a low centre of gravity. Notable features included 150mm brakes inside full-width hubs, fully-enclosed final drive, deep section mudguards and efficient silencing. It was an advanced concept.
The output of the 48 x 54mm twin was a modest 9bhp. The top speed of the 195cc model was around 65mph, largely the result of a considerable weight penalty. The M200 had a dry weight of 297 pounds, compared to the spindly M100's 121 pounds. Even with only 3.7bhp on tap the earlier model would do 34mph.
In the same frame, and of a similar design, a new single-cylinder Adler completed the 1952 range. The M150 had a capacity of 147.6cc (54 x 59mm) and produced 6.7bhp. A full 250 version of the twin followed in 1953: the 54 x 54mm M250 with an output of 12bhp at 5600rpm. It was on a par with the other German 250s of the day with the exception of NSU's 17bhp Max, an ohc single.
The M250 was accepted by riders as the first modern sports two-stroke.
The Adler attracted a lot of attention both inside and outside Germany. It handled superbly, had matchless acceleration and was both smooth and well-mannered. But it lacked bottom-end and mid-range torque. Its clutch had to be handled gently and it was prone to overheating. Yet it was immediately accepted by sporting riders as the first real modern sports two-stroke in contrast to the products of DKW and TWN.
The choice was two-stroke or four-stroke:
Adler M250 or NSU Max.
The Adler people were sufficiently impressed by the latest NSU product to take up the challenge. Their first step was to form a competition department to show the public the true quality of the Adler twin on race circuits and in Six Days Trials events. Kurt Grasmann, an aero engine expert who had joined the firm to work on motorcycles, began to work on the gas-flow characteristics of the two-stroke. In conjunction with the Eberspacher silencer company he obtained some interesting results by experimenting with varying intake and exhaust tract lengths and different expansion chambers.
At the same time, similar things were happening elsewhere in West Germany, at Ingolstadt in DKW's race shop. The basic foundations of modern two-stroke development and tuning technology were being laid.
Working on the rolling chassis of the proposed Adler racer was Jan Friedrich Drkosch, who also contributed articles to the German motorcycle magazine Motorrad. Again, a lightweight tubular cradle frame was selected, along with hydraulically-damped leading-link front forks.
With an output of about 24-26bhp as a result of fitting redesigned cylinders fed by 24mm Amal TT carburettors, the Adler 250RS showed some promise. But 1954 was the year of the all-conquering NSU racing team and for private entrants there was an improvement on the Max, the Sportmax. However, the Adler-mounted Helmut Hallmeier and Walter Vogel gained some good racing results, including third and sixth places respectively in the German GP at Solitude. But only much later - after Adler had quit motorcycling - did the privately prepared water-cooled twins of Gunter Beer and Dieter Falk really show the Adler's true potential, with Falk fifth in the 1958 250cc world championship.
Race shop advances were fed into production models. The RS was available to privateer racers in limited numbers. Among the seven-model range for 1954 only the old M100 and the M2011 were familiar. The M2011 was an enlarged M150 with a 199cc engine in the same frame complete with the clock spring front forks. Along with larger fuel tanks (12 litres to 15 litres), bigger brakes (up to 180mm) and single-spring saddles, the most important improvements concerned new front forks and more highly-tuned engines.
The new MB range included two singles, the 8bhp MB150 and 10bhp MB201. There were two twins: the MB200 and MB250. New pistons and specially-tuned high-level exhausts pushed the 250's output up from 16bhp to 18bhp at 5750rpm.
Friedrich saw no need to go for a new swinging arm rear end. For Adler's plunger design not only featured hydraulic damping but also a variable spring rate, adjusted by turning a knurled knob on top of each unit. Nor did he opt for conventional telescopic forks when the more powerful Adlers required improved front suspension. Instead he produced a complete redesign of the leading-link arrangement with coil springs, hydraulic damping and nearly four inches of travel.
This turned out to be one of the very best front forks on the market. But they were expensive to produce.
Now the Adler really could out-handle the opposition on the road and the performance of the MB250S put it on level terms with an NSU Max. A top speed of 75mph wasn't bad, but the rapid Adler cost about 20 per cent more than the NSU. The cheaper MB250 was only good for 70mph. Disparities between relative price and performance were to count for a lot when motorcycle sales began to decline in 1955.
The revvy, highly-strung behaviour of the two-stroke twins, loved by some and loathed by others, suiting the sporting enthusiast. But he also looked askance at plunger rear suspension on such expensive machines. Commuting riders tended to opt for the torquey singles of other makers. Adler's single-cylinder models sold slowly. It was not a situation that boded well for the future.
Meanwhile, Adler was busy developing a completely different kind of vehicle. Scooters had sold well in Germany since the first Vespas and Lambrettas were imported from Italy in the early 'fifties. Hoffmann and NSU were quick to negotiate arrangements whereby they produced Italian designs under licence. All the other motorcycle makers wanted to get in on the act, but were slow in developing their own scooters.
The Adler Junior scooter was provided with a fan-cooled version of the old M100 engine, 14in wheels and swinging-arm suspension front and rear. Although it was well made - like all Adler machines - the scooter was hampered by the declining demand for two-wheelers.
After 1955 the sales slide began to look ever more serious. Only Kriedler and Sachs continued to thrive on 50cc moped production. Then, at long last, Adler produced a redesigned frame on the new Favorit 250MB and Sprinter 250MBS models during 1956.
The heavy tubular arrangement used to convert the old chassis to swinging arm had none of Adler's usual elegance. While the 18bhp Sprinter gained a dualseat, its weight rose dramatically from 320 to 375 pounds, really taking the edge off the performance of what should have been the fastest 250 around.
In 1957 the Frankfurt Adler works, together with Triumph of Nuremberg, was bought by Grundig, Germany's largest producer of radios and television sets. Triumph and Adler were to join forces in the office machinery market. Their motorcycle departments were immediately closed and the remaining stock of machines sold through common sales network of Triumph-Adler-Hercules. Hercules survived as part of the Sachs concern, lending its name to a Wankel-engined machine in the 1970s.
It would have been very difficult for a small company like Adler to survive the sales slump of the 1950s. BMW had the car side to turn to; Maico sold most of its 250s to the German army; Hercules, Kreidler and Zundapp flourished on moped sales. It wasn't until the first two-stroke twins arrived from Japan in the early 'sixties that the valuable contribution of Adler's designers and engineers came to be fully appreciated.
For, like Val Page
and Bernard Knight of Ariel before them, the people at Suzuki and Yamaha
had studied the MB250 from Frankfurt
in depth before putting pencil to paper. In the Ariel Leader, the Yamaha
YD1 and the Suzuki Colleda we can see designs that bear more than a passing
resemblance. The Eagle might have landed for the last time, but its offspring
soared on.
by Stefan Knittel
(many thanks to Stefan Knittel for giving me permission to reproduce this article)
1957 - (from BMW history) - "Things go from bad to worse this
year. Total motorcycle production at BMW drops yet again - from 15,000
to 5,429 this time. Rival manufacturers like Adler, DKW and Horex
all scrap motorcycle production in general. BMW pulls back from designing
new models, focusing instead on shipping the majority of its machines
overseas to the United States or to England."
Yamaha
In the mid-fifties, as Yamaha Motors began planning its first 250 cc bike,
the model chosen as its target was the MB250 of the German maker
Adler. Powered by a 2-cylinder 2-stroke engine, this machine was
a masterpiece of design and engineering that had won a strong reputation
among European riders. At Yamaha Motors it had been decided to copy the
basic engineering specs of this model and add some unique exterior design
touches.
Those were times when most of the other Japanese makers were also copying
the front-running motorcycle models of the advanced German makers and
introducing one new model after another based on these German machines.
This was surely a necessary step along the way to postwar recovery for
the domestic Japanese motorcycle industry.
Drawing on the example of the Adler MB250, the YD-1's engine was
a 2-cylinder design. Building a 2-cylinder engine was a new challenge
for Yamaha and when it went into the design stage no other Japanese maker
had yet built a 2-stroke 2-cylinder engine. Although the Adler
was used as a model, components like the clutch assembly and dynamo were
given original Yamaha designs in order to create a more compact engine.
The first YD-1 came off the production line in February of 1957.
