Gerhard Macher (born 1905) was operations manager of the Bittrich DKW agency on Schloßplatz in Berlin in the early 1930s. An enthusiastic sportsman, he became one of the top drivers of the DKW works team at that time and proved himself a creative technician for tuning and modifying vehicles for competition.
Thanks to his connections in the testing department in Zschopau and the DKW Spandauwerkes, to influence the development of works racing vehicles. As a result, he received support from the factory in the construction of his competition cars, which were built at his own expense.
At the Monte Carlo Rally in 1929 he drove a DKW P-15 with Gustav Menz as a co-driver. Driving the same car at Koenigsberg the next year, he was all over the ice and snow. The unsatisfactory results at Koenigsberg led DKW to think about how they could improve rally performance in the future.
It was not until 1933, when Macher saw the experimental rear-engine DKW streamlined coupe, that he gained inspiration for the GM bi-motor competition car concept. The DKW 'Aero' was powered by a 600cc rear mounted engine but was discarded after trials due to serious performance defects.
https://dkwautounionproject.blogspot.com/2017/07/dkws-1933-rear-engine-streamliner.html
Macher saw the potential of a twin-engine rally car with front, rear or all-wheel drive, to tackle difficult weather and road conditions more successfully. After two years development, in 1935 Macher appeared at the start of the Monte Carlo Rally, in his first "GM" Spezial, which combined parts from a DKW "Meisterklasse" and the DKW rear engine prototype. The car was constructed from a "Meisterklasse" chassis with a 700 ccm two-cylinder two-stroke engine mounted in the front. A similar drive unit was installed in the rear, rotated 180 degrees. The conversion of the starter and alternator caused this engine to rotate in the opposite direction. The functions of the clutch, gearshift and throttle linkages had been changed so skillfully that they could be used to operate both engines at the same time. Macher was happy to accept that the "ear coolers" protruding from the bodywork on both sides in front of the rear fenders because they provided efficient cooling, even though they spoiled the overall impression of the coupe. When accelerating, the front motor started first, which of course required a high degree of careful adjusting and fine-tuning. The two motors together produced around 50 hp, which combined with the body’s light construction of synthetic leather-covered plywood for a total weight of 1100 kg, enabled a top speed of 125 to 130 km/h to be achieved.
Gerhard Macher explained the development of his car in the AAZ magazine, No. 6, Feb. 1936.
"I am often asked what prompted me to build my DKW special with two engines. In a nutshell, in addition to my interest in the constructive work itself, it was especially my desire to compensate for the great handicap that every DKW driver is forced to accept at international competitions. Since the international classification seldom has a subdivision of the 1½ liter class and the DKW manufacturer often competes with opponents who have more than twice the cylinder capacity and thus the corresponding extra power. The possible power from the additional 800 ccm engine capacity shortfall would be very helpful.
While those in the know about motorsport watched with excitement the small DKW two-cylinder two-stroke engines battle for international sporting status against rivals fielding often the twice the power. Despite the inequality of forces, the general public’s evaluation of the final results are not unaware of this fact.
My two-engine four-wheel drive should now help to balance the requirements of the international motorsport competition. The basis for the construction of this car was a standard DKW-Meisterklasse chassis, which was only changed in the rear axle for the installation of a second engine. This second standard DKW engine, was reversed in its direction of rotation by reversing the cylinder block and changing the rotation of the starter and alternator accordingly. The clutch, gearshift and throttle cables are connected to both engines, so that both engines are operated equally with the same controls.
Since a two-seater body was intended from the outset, the standard wheelbase could also be retained. A modified front axle was used for the rear drive. This now two-engine chassis was given a streamlined body, with particular emphasis on good visibility. For the first time, a flexible (curved) windshield made of Plexiglas (synthetic resin) was installed.
Since the main task of the car is to participate in national and international long-distance competitions, particularly suitable headlights and fog lamps were provided for this purpose. Two large tanks, each with a capacity of 60 litres, give the car a radius of around 1000 km.
The total weight of the car including water and 120 litres of fuel as well as six tires and complete tools is 1099 kg.
The experience I have had with the car so far, especially in Northern Europe, has shown that the car performs admirably in comparison to other cars. Another essential factor in assessing the car is its fabulous acceleration. This acceleration is not only a result of the existing power (PS), but rather due to the simultaneous application of power on all four wheels.
Although the current version of the car has a top speed of only 125 km and a sustained speed of around 118 km, hourly averages of almost 80 km could easily be achieved on routes such as from Berlin to Harzburg.
So that both engines do not interfere with each other when the accelerator is released (idling), the front engine was installed with the standard freewheel and the rear engine without freewheel. However, this also simultaneously eliminates the possibly unfavorable effect of two differentials, because both motors start one after the other with a short difference during acceleration, namely first the front and then the rear motor. All of the advantages that were ascertained so far would of course have an even more favorable effect compared to other equally powerful vehicles with the increase in the number of horsepower. It remains to be said that the car's small engines (as they are divided) are only loaded to 50 percent and this enables a high permanent load without significant signs of wear and tear. The construction of the car is carried out with completely standard parts. Although it is progressive, new and can easily cope with the performance of a superb sports car in the 1½ litre class, it is by no means sensitive. The fuel consumption for both engines (50 HP) together is 12 litres per 100 km.
While there have been some small set backs, from which no new design is ever spared, this cannot stop me in my further work. I am sure I will still have to modify some mechanical parts, for example, I designed a new electrical circuit that is now being installed. In summary, I would like to emphasize that the expectations I set for the construction of this new type of vehicle have been fulfilled.
Gerhard Macher."
In 1937 a certain chief engineer, Max Claus from Reinsdorf near Zwickau, followed in Macher's footsteps. He also converted a "Meisterklasse" into a "bimotor" by installing a complete second drive unit (600 ccm) in the trunk, driving the rear-wheels. The typical, DKW high-lying transverse leaf spring was left in place. A second radiator was not used and the coolant for both engines circulated by means of a water pump through two large-calibre metal hoses through the radiator of the front mounted 700 cc unit. Both clutches were operated with a foot pedal and the two transmissions were operated via a common gear lever. A separate accelerator pedal was provided for each engine, but they could also be operated together. Since both engines had a freewheel feature, one or the other engine could be operated while the other was idling.
With its 38 hp, the car managed a 120 km/h. Claus praised the relatively low fuel consumption, the high mobility and the excellent mountaineering qualities of his four-wheel drive vehicle.
At that time, DKW did not draw any practical conclusions from these experiments. That was probably a good thing, if you remember the insurmountable difficulties other German manufacturers experienced during the Second World War with their complicated and immature all-wheel drive vehicles demanded by the theorists of the Army Weapons Office. It wasn't until twenty years later that the four-wheel drive automobile DKW Munga was finally offered.
https://dkwautounionproject.blogspot.com/2023/03/the-gerhard-macher-bi-motor-special.html
The excellent Auto-Cult model company will release a 1/43 scale model of the GM Spezial in mid-September 2021. https://www.autocult-models.de/models/autocult-05032/
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