Photo ou archives : F-M. Dumas
250 Max - 1953
One cylinder- four driving rods!
After the end of WWII, many manufacturers resumed production of their prewar models in virtually unchanged form. Technical innovation had to wait for the next generation of motorcycles such as the NSU 250 Max, launched in 1952.
The outstanding feature of the Max was its power unit. Its overhead-camshaft was driven from the tail of the crankshaft by two long rods driven by eccentrics offset by 90 degrees. A third rod supported the camshaft bearing, insulating the cam drive-train from variations caused by thermal expansion, ensuring the valve clearances stayed constant.
Silent and Maintenance-Free
This layout, unique in motorcycle history (and costly), had the advantage of being silent, maintenance-free and incapable of going out of adjustment. Though the NSU Max appeared in 1952, serious production only got under way in 1953, and rose to some 25,000 units. Initially, the engine developed some 18.4 hp at 6700 rpm, but around 1954, the compression ratio was reduced slightly to eliminate knocking caused by low-grade fuel, and power rating slumped to 17 hp at 6500 rpm. The frame was also unorthodox, with leading link front suspension and swing arm rear suspension with a large central spring. The springs were concealed within the pressed-steel frame. The NSU Max was successful in European competition.
Engine: 247cc (69x66mm) air-cooled single-cylinder four-stroke
Power Rating: 18.4 hp @ 6700 rpm
Valves: overhead-camshaft driven by eccentrics
Fuel System: 26mm Bing carburetor
Transmission: 4-speed; dry four-plate clutch; chain final drive
Suspension: leading link (front); swing arm with central spring (rear)
Brakes: drum (front & rear)
Wheels: 3.25x19 inch wire (from & rear)
Weight: 320 lb
Maximum Speed: 78 mph
Still modern in appearance: it's hard to believe that the NSU Max, with its unique camshaft drive, was designed in the 1950s.