The Big DKW 4=8

DKW made its automotive name with its range of small, two-stroke engined, front wheel drive cars. The F (Front) series was introduced in 1930 and went through a rapid evolution to become the second best-selling car in Germany by 1935. However, DKW also produced a range of mid-sized cars targeting the more affluent middle class in a separate factory in Spandau, near Berlin. Imaginatively named “the Big DKWs” the range was fraught with problems and did not enjoy market success. Nevertheless, DKW persisted with the range right up to 1940 when all car production was stopped.

Inherent problems of the two-stroke
DKW founder Jorge Rasmussen was convinced by the efficiency and simplicity of the two-stroke engine, but although they were light and relatively powerful for their size, all two-stroke engines had inherent problems with thermal efficiency and the loss of un-burnt fuel. Many companies tried a variety of different solutions, such as deflector pistons, adjusting the port positioning, and different gas-flow solutions but none of these solutions were entirely satisfactory.

In 1927 DKW introduced a 500cc twin cylinder Z-range air cooled engine. The Z-range used deflector pistons to improve gas flow in the combustion chamber, but this solution overheating to the rear of the cylinders with prolonged use. To address the overheating DKW installed a water jacket around the engine, changing it from air-cooled to water-cooled. Water-cooling however added substantially to the weight of the engine, making it too heavy for a motorcycle engine but was potentially suitable for use in a small car.

The Z range were DKW's only water cooled motorcycles. Cooling was effected via a small radiator mounted ahead of the engine, but it was not a particularly effective solution and the company quickly abandoned the engine for motorcycles.

DKW's first car

DKW had experimentally fitted single cylinder two-stroke engines to Slaby-Beringer elektrowagens in the mid 1920s, but this proved to be disappointing. The new Z-range engine however appeared to be robust enough to power a small size car and in 1928 DKW unveiled the P-15 cabriolet. The car was powered by Z-range engine a of 600cc capacity, delivering 15 brake horsepower. The engine was mounted in-line and power was delivered to the rear wheels via a traditional prop shaft and differential. The car itself was constructed as a self-supporting plywood box and did not have a chassis. Nevertheless, P-15 filled an important market niche and over 3000 cars sold.

Technically however, the Z-range engine wasn't entirely satisfactory so DKW continued to investigate other solutions. One option to improve combustive efficiency was to use a charging pump to fill and clear the cylinders. In this solution gas was sucked into a pump cylinder, compressed by a piston and then injected into the combustion cylinder for ignition. This method was used with success by DKW's motorcycle racing division.

Schematic of the V4 engine. The charging pistons are at the front of the engine, on the right. The pistons were driven by the crankshaft like the power cylinders, but without ignition.

The new engine comprised two three-cylinder engine blocks in a V arrangement driving a central crankshaft. The first two cylinders were charging pumps that received and compressed the fuel mixture before pumping it into the four combustion cylinders. The new engine was a much more substantial beast than its two cylinder predecessor, with nominal 1000cc capacity delivering an estimated 25 brake horsepower. One of the drawbacks of the design was that the crankcase was not lubricated by the petroil mix, requiring a sump and splash lubrication system.

The new car to carry the new engine was substantially bigger than the P-15, construction methods were the same however, being a chassis-less, self-supporting plywood box. The engine was mounted inline, driving the rear wheels via a differential. The gear shift was floor mounted, directly to the back of the gearbox. The car came in two seater, two door, four seater two door and four door limousine versions.

The 4=8 hit the market in 1929 – just in time for the Wall Street Crash. The economic downturn that followed helped suppress sales of the Big DKW, which were lukewarm at best. The car's engine was too complex and still experimental. Owners who failed to monitor oil levels in the sump – something that did not exist in other two-stroke engines – burned out their cranks. Even when maintained properly the engine was noisy, and vibrated excessively and consumed both fuel and spark plugs at a prodigious rate. Damage to the plywood structural members due to vibration was commonplace and, as the car had no chassis, was problematic to repair.

Rasmussen looks to break into a new market – in vain
In the meantime, DKW’s energetic director, Jorge Rasmussen, had been busily expanding his business empire. In 1927 he had traveled to the US where be bought up the bankrupt Rickenbacker motor car company. His sole intent behind the purchase was to sell the company’s 6 cylinder four-stroke engine to other German manufacturers. Rickenbacker’s plant and designs were dismantled and shipped to Germany.

World War I flying ace Eddie Rickenbacker with his 1924 Rickenbacker coupe. Rickenbacker lent his name and face to the company but otherwise was not involved with the business.

On his return, he was presented with another opportunity, this time in the form of the insolvent Audi motor company. Rasmussen’s financiers, the Bank of Saxony, were desperate to offload the company before it went bankrupt and encouraged Rasmussen to buy the ailing company in 1928.

1927 Audi 14 50ps. Before Rasmussen bought the company Audi's sales were pitifully low - around 20 cars per year.

However, if Rasmussen believed that Audi and Rickenbacker could be made to fill the gap that the Big DKW was designed to fulfill, he was to be sadly mistaken. Despite all the cost and effort involved in setting up the Rickenbacker plant in Germany, when the engines finally began rolling of the production line they failed to attract any buyers. Production was stopped by 1930.

Audi was much worse state than Rasmussen was led to believe. He was forced to ruthlessly purge the company of its expensive and unsaleable models. He shut down Audi’s engine plant and installed his surplus Rickenbacker engines on two new Audi models, the SS and Dresden. Neither car found a market and less than 100 were built between 1931 and 32.

Rasmussen's last throw of the Audi dice - the Audi P

Rasmussen's last throw of the Audi dice was to re-engine a DKW 4=8 with a 1.2 litre Peugeot four cylinder engine and badge it as the Audi P. However, even this car failed to draw a market as customers preferred the troublesome two-stroke engine of the DKW 4=8 car over the Audi car by a margin of 10 to 1.

The Audi P and DKW 4=8 side by side highlights the similarity between the models.

The radical gamble

After the failure of the Audi P, in October 1930 Rasmussen charged his design team to develop a new budget car that would undercut everything else in the market in time for the February 1931 Berlin Motor Show. The resulting car was a masterpiece of efficiency. The differential and prop shaft were dispensed with in favour of from wheel drive; the little two cylinder engine turned 90 degrees and mounted transversely across the frame to simplify the transmission. A smart roadster body was mounted on a simple ladder chassis. Apart from the radical decision to employ front wheel drive – the first in a production car – the car’s most important feature was its newly designed two-stroke engine.

In 1929 Rasmussen had come across an engineering patent by Dr Adolf Schnerle for a reverse scavenging two-stroke engine cycle. Schnerle was an academic engineer and had proposed the reverse scavenging concept as a technical exercise to improve heat exchange and efficiency in two-stroke engines. He published his paper, lodged a patent and went back to academic research. Rasmussen instantly recognized that the Schnerle patent could significantly improve two-stroke engine performance and reduce manufacturing costs. He rushed to meet with Schnerle and secured an exclusive licensing arrangement for DKW. As anticipated, DKW’s new Schnerle engines realised a significant uplift in performance, endurance and fuel economy and instantly made every other two-stroke engine obsolete.

The DKW F1 (Frontreib) was an instant success and the P-15, PS600 and 4=8 were all retired. The Audi plant at Zwickau was given over to production of the new car.

The Poor Cousin

DKW’s Spandau plant was primarily a coachwork plant. It was here that the wooden bodies of the F1 and its successors were built before they were shipped off to Zwickau and fitted to their chassis. However, one small corner of the factory however remained dedicated to the Big DKW.

After the first version of the 4=8 had been released and the problems with the engine became evident, DKW reduced the engine to 800cc capacity. Fuel and spark plug consumption were not improved however, so the following year a 990cc capacity engine was reintroduced. Performance remained problematic.

In 1932 the car was rebranded the Sonderklasse 1001. The wheelbase was lengthened to 2800cms and the bodywork given more modern styling. To improve the car’s handling the Sonderklasse introduced DKW’s new transverse floating rear axle, called the schwebeachsel. This did improve the ride but combined with the longer wheelbase stretched the chassis-less body to its outer limits and when placed under great stress the car exhibited a disturbing tendency to break in two. Nevertheless, the car continued to find a market, albeit in much lower numbers than its Front stablemate. The Sonderklasse was still a more economical car than a contemporary Wanderer, however, engine warranty repairs for the Sonderklasse became an industry unto themselves.

This contemporary cigarette card shows the self supporting wooden body and chassis.

The 4=8 engine

The Floating Car

The mid-1930s saw the beginning of the streamlining movement and in 1935 DKW unveiled its contribution – the Schwebeklasse. The Schwebeklasse was the replacement for the Sonderklasse. Although the engine and gearbox was unchanged, the body was completely new. The Schwebeklasse also introduced floating axles on front and rear, which DKW made much of via highly publicized cross country trials. Here again though, the car could not escape its fundamental underlying weakness. The chassis-less body fractured under stress and the engine continued to perform poorly. A later version with a bored out 1054cc engine failed to improve its performance.

A cigarette card of the Scwebeklasse

The last throw
In the years after the National Socialists took power in 1933 Germany’s economy substantially improved. In 1934 Adolf Hitler personally promoted the idea of a ‘people’s car’ and was very specific in his expectations. The German people’s car would be modern, steel car, not a wooden or baby car. This pretty much excluded DKW’s entire range from consideration so DKW’s design bureau went into overdrive to develop the next generation of vehicles. For the Front range, DKW began working on an entirely new steel bodied car powered by a three cylinder two-stroke engine. This would be unveiled in 1939 as the DKW F9; the car that would restore DKW’s fortunes in post-war Germany.

Auto-Union's design bureau saw another opportunity to hit the market early. Wanderer already had a small middle-class car in the market in their W24 model. Re-engining the car with a two-stroke engine would go some way to reducing its cost, although nowhere near Hitler’s proposed 1000RM pricetag. DKW’s new 3=6 engine was the perfect candidate for the car but it was not yet ready for production so the 4=8 engine was substituted instead. The new car, which was marketed as the new Sonderklasse, went on sale in 1937. Sales of the new car were reasonable, but were massively outstripped by the DKW F8. Auto-Union also came to regret their decision to use the 4=8 engine. The increased weight of the steel car added pressure on the engine, accelerating its propensity for crankshaft failure. To maintain sales customers were offered two free engine replacements. After the third engine failure they were given a replacement Wanderer engine.

The 1937 Sonderklasse was basically a Wanderer W24 coupe with a two-stroke engine and different radiator grill. At 3100RM the Sonderklasse was 750RM cheaper than the basic Wanderer.

Sales continued to tick over until all Auto-Union passenger car production was shut down in 1940 and the factories given over to war production. Due to their mechanical unreliability, few 4=8 cars remain today. Obviously the chassis-less wooden bodied cars were lost to rot and fire, while most of the steel bodied Sonderklasse were lost in the war.

Why did DKW persist with what was obviously a flawed design for so long? I suspect DKW wanted to retain a larger model in the market, but had no alternative powerplant to work with. They had tried to increase the bore of the two cylinder 700cc engine but encountered limitations with its performance. The 3=6 was first designed in 1936 but took several years of development to perfect. The 4=8, although a poorly performing engine, was at least available. Surprisingly, customers seem not to have been put off by the car’s engine problems and they always found a market, albeit much smaller than the market for the smaller Front model. In the course of its 10 year production run, approximately 40,000 4=8 cars of all models were produced.