Mercedes-Knight 16/45 hp touring car, 1913
What appears to be a technical aberration from today's point of view was, in the first decade of the 20th century, a tempting option that promised to bring competitive advantages - at least in the area of mass-produced automobiles. We are talking about the slide-valve spark-ignition engine, which was used quite successfully at Daimler-Motoren-Gesellschaft (DMG) for almost a decade and a half.
Instead of conventional valves, which are arranged in an overhead or upright position and are actuated via a camshaft, the gas exchange in these unusual engines took place via two cylindrical sleeve valves, which were arranged between the cylinder wall and piston and moved up and down with the combustion cycle. This unusual technical solution had been the brainchild of the US American Charles Y. Knight as far back as 1903. DMG chief engineer Paul Daimler was also fascinated by the advantages of this concept and even acquired a number of relevant patents in 1908 and 1909 through his own intensive work on slide-valve control. When the opportunity arose to acquire production licences for Knight's slide-valve engine after extensive, positive test stand runs, DMG seized it.
The special characteristics of the slide-valve engine were particularly suited to perfecting the character of comfortable touring cars from the upper and top segments of the model range. It was not so much the absolute peak performance of the drivetrain that was required here, but rather cultivated, particularly quiet running and superior power delivery even from the lowest engine speeds - in this respect, conventional valve-controlled engines still had some deficits at the time. The disadvantages of the slide-valve control - for example issues with the sealing, high demands on the lubrication circuit and a limited turning capacity - were not yet very significant at the speed level achievable at the time. It was only with the sustained development of the combustion engine in the field of aviation during the First World War and the subsequent continual increase in the speed of car engines that the technology of slide-valve engines became increasingly obsolete and their use was relegated to a few narrow niches.
After its presentation at the Paris Motor Show in December 1910, DMG's first series-produced model with a slide-valve engine, the Knight system, went into production at the beginning of 1911. Its engine was a slightly long-stroke four-cylinder with a displacement of 4.1 litres, which, with an output of 45 hp/33 kW at 1750 rpm, did not need to shy away from comparison with valve-controlled engines. Two years later, a 2.6-litre version with 30 hp/22 kW and a 6.3-litre version with 65 hp/48 kW were added to the engine range.
The slide-valve engines were installed in touring cars bearing the brand name Mercedes-Knight. The 10/30 hp, 16/40 hp and 25/65 hp models formed a separate model family within the Mercedes passenger car portfolio. Despite the high production and maintenance costs as well as the fundamentally tricky technology, there was a customer base that remained convinced by these cars, which DMG served for a total of 14 years. The 10/30 hp and 25/65 hp models were only produced until 1915, but the 4-litre model remained in the range until 1924. The total number of Mercedes-Knight models built during this period totalled more than 5500 vehicles.
In mid-1913, the successful 16/40 hp model was renamed the Mercedes-Knight 16/45 hp, and some of these cars were even used in motor racing without any modifications being made to the standard engine. The Belgian DMG importer Théodore Pilette in particular excelled here and proved that some of the special qualities of the slide-valve-operated Knight engines could have an advantageous effect in racing.
One outstanding example was Pilette's bold entry for the 500 miles of Indianapolis, which was held for the third time on 30 May 1913. The Belgian, whose 16/45 hp racing car had the smallest capacity and least powerful engine in the entire starting field, qualified for the race with the lowest speed. However, the reliability and, above all, the low fuel consumption of the Knight engine paid off over the race distance: without having to make a single pit stop, Pilette crossed the finish line in a sensational fifth place after 07:19 hours. Over the 500 miles, the Mercedes-Knight consumed an average of just 11.8 litres/100 km.
Pilette's compatriot Léon Elskamp also made a name for himself in 1912 and 1913 as a competent driver of the Mercedes-Knight who knew how to exploit the strengths of the design. At the end of June 1913, for example, he succeeded in winning the racing car class up to 4.5 litres with a speed of 116.5 km/h in a 16/45 hp at the race week in the Belgian seaside resort of Ostend.