Mercedes-Benz M21 engine

The side-valve six-cylinder engine had a capacity of 1,961 cc which produced a claimed maximum output of 40 PS (29 kW; 39 hp) at 3,200 rpm. The engine shared its 85 mm (3.3 in) piston stroke length with the smaller 6-cylinder unit fitted in the manufacturer's W15 model, but for the W21 the bore was increased by 5 mm (0.20 in) to 70 mm (2.8 in). The stated top speed was 98 km/h (61 mph) for the standard length and 95 km/h (59 mph) for the long bodied cars. Power from the engine passed to the rear wheels through a four-speed manual transmission in which the top gear was effectively an overdrive ratio. The top two ratios featured synchromesh. The brakes operated on all four wheels via a hydraulic linkage.^[8]

During the model's final year, Mercedes-Benz announced, in June 1936, the option of a more powerful 2,229 cc 55 PS (40 kW; 54 hp) engine, which was seen as a necessary response to criticism of the car's leisurely performance in long bodied form.^[9]

• Mercedes-Benz W21