The first test engine, the G 1, was followed by two other designs which were not ready for mass production before an engine that would literally break new ground in mobility was put to the test in 1923: the G 4. It was the logical response to the design challenges that Karl Maybach and his team had faced in their previous constructions.
The changes were correspondingly massive: The crankcase was made slimmer at the top, cylinders, water jackets and cylinder heads were combined into a single casting, the so-called block cylinder. These were in turn hooked into the upper part of the crankcase. In order to achieve a higher load capacity, it was also decided to use rolling bearings for the engine (crankshaft, connecting rod (hub bearing)) – the materials used for plain bearings at the time had not withstood the stresses. In addition, the camshaft was installed in the cylinder head; compressors, injection valves and their arrangement were also revised.
The result was impressive: Already the first version of the engine, the G4a, achieved an output of 150 hp at 1300 revolutions per minute – an output coupled with high engine speeds that had not been seen before in diesel engines. The world’s first high-speed diesel engine went into production in 1924. The G 4a and its successor, the G 4b, became a milestone in the history of mobility, but not only because of its performance. They were also amazingly versatile. At the same time as the rail version of the G 4a, Maybach also launched a version for boats. The engineers thought of the powertrain as a unit: that is why they developed a marine reversing transmission with the designation UR 1/2 and the mechanical four-speed T 1 gearbox for rail drives. The next drumbeat followed already in 1927: the G 4b even delivered 175 hp at 1400 revolutions per minute. The regulations of the Versailles Treaty no longer applied, which is why it was possible to improve the mass-power ratio again with a light metal housing.
New territory was also broken in the development of the powertrain for locomotives. In order to ensure an organic interaction of the drive train with the railcar as a complete unit, it was decided to cooperate directly with the Wismar wagon factory of Eisenbahn Verkehrsmittel AG Berlin (E.V.A.). More about the E.V.A. Maybach railcar in the last part of this series.
Source and also an important reading tip for further reading: Wilhelm Treue, Stefan Zima: Hochleistungsmotoren. VDI Verlag: Düsseldorf, 1992. You can purchase the book at an antiquarian. We would like to point out in particular that an extended new edition of the book is planned.
Photo: MTU Friedrichshafen GmbH
Maybach Diesel engine Type 4a