The affordable car problem seemed to be solved. In the years following the completed merger between Benz and Daimler in 1926, in which BMW was a minor partner, those companies and some of their shareholders planned to add a small-car specialist to their grouping. They had their eye on Opel, a family-owned company that was Germany’s most prolific small-car builder. With Opel protecting their popular-car flank, they could concentrate on the senior models that made their names.
They reckoned without General Motors. After several survey visits the American company bought control of Opel for $30 million in March 1929. For Daimler-Benz this was a challenge. In the final years of Ferdinand Porsche’s technical stewardship, ending in 1928, the DBAG had spurned his proposals for smaller cars, saying that the required investment would be excessive.
During a board meeting in June of 1931 Emil Georg von Stauss, representing the Deutsche Bank, said, "Earlier small-car plans were not implemented because the necessary investment of millions was described as unacceptable at the time. The risk to the corporation is probably less if you build a cheaper car than if you don’t have it and then get pushed out of the market." He was stating this after the fact, for from 1929 work had progressed at Daimler-Benz’s Untertürkheim headquarters on two sizes of small cars.
Imagining a rear-engine Mercedes
At the DBAG, ex-Benz man Max Wagner was in charge of chassis design. He was rightly proud of his 1923 Benz racing car’s rear swing axles and inboard brakes. At Untertürkheim he liked to show new colleagues the solid-gold medallion he was awarded by the Monza organizers for the most outstanding new car in their 1923 Italian Grand Prix. When Mercedes decided that it needed to build a new small car, Wagner unabashedly placed its engine in the rear.
The idea of rear engines for small cars was on many minds in the 1920s. One of the most persuasive advocates of this design direction was engineer Josef Ganz, from 1928 the editor of the magazine he renamed Motor-Kritik. No issue lacked his praise of such advanced designs as Benz’s mid-engined racer, surviving examples of which Ganz helped to preserve.
As a courtesy in 1931 Daimler-Benz asked Ganz to consult on some aspects of the new Type 170 they introduced that year, which had Ganz-type parallel-leaf-spring front suspension. As well they invited a visit to Untertürkheim near the end of 1931 by Ganz with one of his vehicles, its diminutive size in line with its nickname of “Mayfly.”
This wasn’t Daimler-Benz’s first brush with the idea of smaller cars. The merged company had plenty of larger models but struggled when it turned to the idea of a smaller auto that it might make in volume to earn some money by fully utilizing its many factories. Some of the last projects of Ferdinand Porsche, who arrived in 1923 and left in 1928, were small cars. One, dubbed the 5/25, was powered by an overhead-valve six of 1,392 cc. Built in a test series of 30 cars in 1927 to be evaluated by company executives, it didn’t go forward for the financial reasons mentioned earlier.
In 1928 Porsche’s attention turned to a 1.3-liter four-cylinder prototype of conventional layout as well as a more radical concept: a rear-engined car with independent suspension and a semi-monocoque body. This idea, which was regarded at Daimler as Porsche’s “unfinished symphony,” didn’t progress beyond the study stage.
When Porsche left, his place as the company’s board member for engineering was taken by veteran Benz engineer Hans Nibel, who moved into Porsche’s Stuttgart villa. Like Wagner, Nibel had worked on the mid-engined Benz racing car. He was a broad-gauged engineer who embraced the exotic when conditions called for him to do so.
The men from Mannheim were in the ascendancy at Daimler-Benz in the wake of the departing Porsche. While Wilhelm Kissel was in charge of the company’s management board, supervisory-board members Emil Georg von Stauss and Karl Jahr also took a close interest in Daimler’s affairs.
The W17 prototypes
Kissel et al assigned Nibel the task of designing a small, inexpensive Mercedes-Benz. He put work into Project W17, and that bore fruit during 1931. Porsche’s valedictory proposal of a rear-engined car—his first such design—may have encouraged consideration, while the Benz men had not only built rear-engined racing cars but also licensed (though never implemented) the production of the rear-powered designs of Edmund Rumpler.
Another influence may have been the work of French engineer Emile Claveau. At the 1926 and 1927 Paris Salons Claveau had shown and demonstrated autos that had their engines in the rear, placed ahead of the differential. This would not have suited the DBAG men, who knew it would be best to place the passengers between the axles for the best ride quality. This required the engine’s placement behind the wheels. The choice would be second-guessed by aforementioned critic Josef Ganz, who thought this resembled more of an “outboard motor” than a true rear-engined design.
Although some patent drawings suggest that the Type W17 had independent front suspension by transverse leaf springs, most sources agree that Max Wagner’s recipe of a solid front axle and swinging rear half-axles for the 1923 Benz racers was perpetuated. Bridging the W17’s 98.4-inch wheelbase was a central steel-tube backbone frame to which the transaxle was solidly attached.
Although not yet mainstream technology, the tubular backbone was already well proven in the Tatras of Hans Ledwinka and the Austro Daimlers of Karl Rabe. Praised for their torsional stiffness, such frames required duplication of the floor and body-supporting function. In the W17 the central tube was bolted both to the front-spring carrier and the transaxle, which was forward of the differential. The large-diameter tube was used to the maximum to carry the clutch rod, gearbox controls and various engine controls.
An air-cooled boxer engine
The Type W17 prototypes carried an engine that differed sharply from anything either Daimler or Benz had previously built: an air-cooled flat-opposed four, commonly known as a “boxer” engine. Here too was a possible link with the Claveau designs, which also had air-cooled side-valve flat-opposed fours. To keep it as short as possible the W17 block had only two main bearings and finned-iron cylinders cast in pairs on each side. Capping each pair was a single finned cylinder head.
Integral with the cylinder pairs were the ports, for this was a side-valve engine whose valves were opened directly by a camshaft located above the crankshaft. The cam was driven by a pair of gears at the four’s anti-drive end. Surrounding the flywheel was a big scirocco-type blower that delivered cooling air through ducts to the heads and cylinders. Several patents showed proposals for ducting cooling air to the W17’s engine bay, including a rooftop inlet that channeled air downward and into the engine bay for a water-cooled version.
Measuring 70 x 78mm, the four-cylinder boxer displaced 1,201cc and was capable of revving to 3,350 rpm. Above its center a single Solex updraft carburetor fed individual pipes that curved down to the four inlet ports. Tubes rising from shrouds around the exhaust pipes brought warm air to the carburetor to help fuel vaporization. With a compression ratio of 5.8:1 it produced 25 horsepower at 3,100 rpm and 50 lb-ft of torque at 1,420 rpm.
Drive from the single-disc clutch went to a shaft that was coaxial with a hollow shaft that served both as the transaxle’s mainshaft and as the input gear of the car’s worm drive. The driven gear was below it. Compactly forward of the final drive was the three-speed gearbox, which housed sliding pinions for low/reverse and second gear. Top gear was a direct drive engaged by a dog clutch.
Lackluster performance
Hard-pressed to cope in laden conditions with a car that weighed 2,245 pounds without passengers, the flat-four gave a top speed of 50 mph. When the Army tested the W17’s military version in 1932 it was unimpressed by its performance over rolling countryside.
Project W17 was only one of the many Daimler-Benz initiatives to get the glassy eye from Max von der Porten, chairman of the supervisory board of Rheinmetall AG, a major supplier to the heavy goods industry. Daimler’s von Stauss invited von der Porten to recommend changes to streamline the far-flung DBAG factories and activities, which had seen little integration since the merger of Benz and Daimler.
Among other topics, the minutes of a meeting with von der Porten on December 17, 1930 addressed the building of W17 prototypes, of which 10 were scheduled. He gained acquiescence to his suggestion that only two should be completed as vehicles while the remaining eight were to finished as parts, to await the results of an eight-day trial of the first pair before their completion. “The final production of the small car,” said the minutes, “should only be undertaken after these cars had been tried out down to the tiniest details. For this purpose Herr von der Porten approved the foreseen building of a preliminary series.”
Two-door body styles built on the W17 chassis included a staid sedan, a convertible, open touring cars and rough-and-ready military versions. One body, a sleek duck-tailed coupe with a rounded hood, was certain to be the work of Erwin Komenda, who joined Daimler from Steyr in 1929 and from there would become one of Ferdinand Porsche’s staunchest allies. However, with acceptance by the military crucial to the W17’s production viability, the project was terminated.
With pressure unrelenting to find a solution to the small-car problem, Daimler-Benz continued mulling the introduction of a new model smaller than its six-cylinder 1.7-liter Type 170, launched at the beginning of 1931. “The times in which we only sold big luxury cars finally seemed to be over,” recalled Josef Müller, chassis engineer under Max Wagner. “A new era of popular motorization was announcing itself. This was reason enough to think anew about the overall design of the car, especially the space utilization, even though it shouldn’t be the kind of ‘drivable platform’ that Josef Ganz, editor of Motor-Kritik, tried to make palatable.”
BMW weighs in
Drawn into Stuttgart’s small-car discussions was a Bavarian aero-engine company, BMW, led by Franz Josef Popp. BMW’s takeover of Austin-Seven-builder Dixi had been encouraged by Emil Georg von Stauss, who invited Popp to serve on the Daimler-Benz supervisory board. Between them, with the support of von Stauss, Daimler-Benz and BMW were trying not to step on each other’s toes. Indeed, Popp and Daimler’s Kissel had drawn up a memorandum of commonality of interest that committed them to coordinate their product programs. In October of 1931 they expanded that understanding to embrace a new thrust in the small-car field.
Although his ex-Dixis were selling fairly well, said Popp, “German buyers had more elevated expectations. Moreover, with their larger-volume production Opel and DKW were able to price more favorably. Since at that time neither Daimler-Benz nor BMW was in a position to finance the series production of a suitable small car, Kissel and I decided to prepare our own designs for larger small cars, indeed of several types to close the gap between small cars and large ones in a common sales program.” As had been the case with Benz from 1924, such a joint marketing effort could eventually lead to a merger of BMW with the corporate structure of its south-German sisters.
Their effort was to be what Kissel called “a flight into quality” to give their products a loftier image than the banal offerings of the American car makers and their German branches, both of which were having a hefty impact on Germany’s car market—up to a penetration of 40 percent, Popp said. “We wanted to set the strength of German engineering artistry against the blatantly commercial approach of the foreign companies,” he added.
“We agreed that Daimler-Benz would develop a 1.3-liter small car, and in two versions: engine in front and rear-engined,” recalled Franz Popp. “BMW would develop two types: an 800cc four-cylinder and 1,200cc six-cylinder. Subsequent testing would decide which models would go into production.” Both companies had the backing of von Stauss, who personally supported these small-car adventures and whose Deutsche Bank granted the credit lines that allowed them to be realized.
Fateful decision
BMW picked the 1.2-liter six-cylinder to develop further while the DBAG chose the rear-mounted 1.3-liter engine. “From a preceding experimental version with an air-cooled boxer engine,” said Josef Müller, referring to the W17, “we already realized that the cylinder block should not be directly bolted to the central cylindrical frame, but rather for noise reduction should be hung elastically in a fork of the frame and possibly water-cooled. Unfortunately, when choosing the engine we still succumbed to the temptation to take the longer, albeit simpler, in-line four-cylinder instead of the short boxer.”
As easily as that, a decision was taken that would blight several families of rear-engined Mercedes-Benz cars with the excess “outboard” weight of in-line water-cooled engines. Against excessive background noise, this important message of Project W17 had not been heard.
