February: Mercedes Grand Prix racing car of 1914.

Mercedes-Benz Classic Calendar2015.
  • Classic Calendar 2015 – February

  • Mercedes Grand Prix racing car of 1914.

    In autumn 1913, Daimler-Motoren-Gesellschaft (DMG) decided to take part in the French Grand Prix to be held on 4 July 1914. In view of the extremely tight time schedule, this decision posed an enormous challenge for the engineers in Untertürkheim, who were called upon to develop completely new cars. So in a manner of speaking, the race for victory in Lyon already began months before the starting gun. But it was not just Mercedes that wanted to win the only Grand Prix in that year's racing calendar. The engineers working for all the other manufacturers taking part were likewise driven to deliver top technical performance.

    Making best use of the possibilities available at the time, DMG developed a particularly progressive, high-tech concept that enabled the car to withstand the sheer torture of more than 750 kilometres under full throttle. The technical options available were extensive: special features such as single and twin overhead camshafts, overhead valves in a V-configuration in hemispherical combustion chambers, desmodromic valve control, combustion chambers with two or four valves and propshaft drive were already used in motor racing at that time. 100 years ago, finding the right mix between advanced, race-winning technology and long-term durability was the major challenge – one that Mercedes met very successfully.

    For the 6th Grand Prix de l’Automobile-Club de France (A.C.F.) the organising club set the rules itself, and also the technical specification for the vehicles taking part, because in 1914 there was not yet an international organisation such as today’s Féderation Internationale de l’Automobile (FIA).

    For the 1914 Grand Prix the permitted overall weight was set at 1100 kilograms and the upper displacement limit at 4500 cubic centimetres. In practice, this meant almost halving the engine displacement compared to the 1913 Grand Prix. In prescribing this the A.C.F. favoured the French manufacturers in the smaller-engine category, who had previously dictated the pace. On the other hand, the race rules published in September 1913 put Daimler-Motoren-Gesellschaft and its chief engineer Paul Daimler under great technical and time pressure.

    The engine of the Grand Prix racing car.

    Restricting the displacement required a significant increase in engine speeds to between 3000 and 3500 rpm. In view of DMG’s experience with critical vibrations in the aircraft engines that had been used in 1913, the engine designers under Paul Daimler decided on a new concept. For the first time, steel cylinders threaded into the cylinder head with welded-on water jackets for each cylinder were used, a design that was to remain characteristic of Mercedes-Benz racing engines for decades to come. This meant that each cylinder received an adequate supply of coolant even in the most critical areas – the cylinder hotspots. The cylinder/cylinder head unit was bolted to the two-section aluminium crankcase.

    Departing from previous cylinder head designs, the engineers employed a four-valve system in the 4.5-litre racing engine – an absolute first at DMG. The overhead valves in a V-configuration with an angle of 60 degrees were controlled by an overhead camshaft. This had three cams per cylinder, as the two intake valves were operated via a forked roller-type rocker arm, but the two exhaust valves by one forked roller-type rocker arm each. For vibration reduction, the five-bearing camshaft was driven from the rear end of the crankshaft by a vertical shaft. The same applied to the drive for the oil pumps and ignition magnets, which was also located at the end of the five-bearing crankshaft, though in this case a transversely arranged pinion shaft was used.

    The pistons of the cars driven by works drivers in the 1914 Grand Prix were still of cast-iron, although attention was already turning to aluminium pistons. Although test-bed runs with the aluminium pistons had been completed successfully, most drivers still opted for cast-iron pistons. The car of the Belgian driver Theodor Pilette had aluminium pistons. Engines were only equipped exclusively with aluminium pistons in 1922, when DMG was preparing the vehicles for the Targa Florio race of that year. These lighter pistons allowed the maximum engine speed to be increased once again from 3200 to 3600 rpm.

    To exclude every possible risk, the designers in Untertürkheim placed a particular emphasis on engine lubrication. The crankshaft was supplied with oil by two adjacent oil pumps, which were likewise located at the end of the crankshaft to minimise vibrations. Both pumps were configured so that they drew oil from the crankcase while also continuously feeding fresh oil into the circuit from a separate tank. A separate oil circuit operated by the driver via a foot-pump was responsible for lubricating the cylinder walls, camshaft and rocker arms. This enormous flow of oil made a commensurate ignition system necessary: three special Eisenmann spark plugs were fitted to ensure optimal ignition of the mixture. Two were on the intake side, one on the exhaust side. These spark plugs featured a centre electrode of Böhler-Rapid high-speed steel and two side electrodes of platinum.

    The newly designed engine proved to be a resounding success – taking the first three places speaks for itself. During the First World War this engine received a further, unintended accolade. On 15 July 1914, the winning car was made available to the British Mercedes distributor Milnes Daimler Ltd for display purposes. Following the outbreak of the First World War the racing car was confiscated, and served as the technical model for the Rolls-Royce Hawk aircraft engine, while the valve assembly was adopted for his first motor engine by William Owen Bentley.

    Until the end of the 1920s the engine was also used successfully in Mercedes racing cars: in 1922, Count Giulio Masetti, an Italian private driver, took overall victory in the Targa Florio in the redesigned Mercedes Grand Prix racing car, now painted in the Italian racing colour of red. In 1924, Count Giovanni Bonmartini won the hill-climbing race at Merluzza, near Rome, in a Mercedes works vehicle, while Count Doenico Antonelli took second place in Masetti’s car. That same year, 1924, also saw the introduction of a completely new combination: at the instigation of the drivers, the output of the engine that had been tried and tested over a period of ten years was increased by adding a compressor and installed in the chassis of the new Targa Florio racing car. The result was a car affectionately christened “Grandma” by the drivers, which went on to deliver top performance time and time again in hill-climbing races. The most notable successes were achieved by Rudolf Caracciola and especially Adolf Rosenberger. These demonstrated that this 4.5-litre racing engine designed in 1913/14 was so robustly conceived from the start that it could also cope without problem with considerably higher power levels.

    The vehicle.

    A rethink was also necessary versus the 1913 design where the chassis was concerned – above all because of the change from chain drive, as used hitherto, to shaft drive. The special feature of the chosen design was two ring gears cast onto the half-shafts, which allowed the rear axle tubes to be slightly slanted. The propeller shaft was attached to the four-speed transmission via a universal joint, and rotated within a torque tube supported by a ball joint mounted on a transverse strut on the frame. This provided longitudinal axle guidance, allowing the axle to move up and down. For the French Grand Prix the vehicles were not yet fitted with brakes on the front wheels – certainly not unusual circumstances for that era, even though four competitors – Peugeot, Delage, Fiat and Piccard-Pictet – joined the lineup with brakes on all four wheels.

    DMG quite consciously chose to do without this innovation: although the vehicles fitted with front-wheel braking may have been faster into the bends, the powerful Mercedes racing cars outclassed their competitors when accelerating out. The omission of the front brakes also resulted in reduced tyre wear and improved handling for Mercedes. It was not until the Targa Florio of 1922 that the Mercedes racing cars would join the starting lineup with brakes all round.