Photo ou archives : D. Prest
500 OSL - 1934
German through and through
The little world of the motorcycle created its own European community long before the politicians had the same idea. So it was that NSU, a pioneer of the German industry, achieved fame on the racing circuits in 1930 with a single overhead camshaft engine developed by Walter Moore, the English engineer who had just created the famous Inter models for Norton Â– and their German successors bore a strong family resemblance. In 1933, NSU profited from the experience gained from competition by introducing the OSL 250, 350, 500 and 600cc which, apart from their overhead-valve heads, were replicas of the overhead cam racers.
Built to Last
German-built quality is legendary: all the components of the OSL were designed for long service without problems. The chain was protected by chaincases, the crankshaft turned in three bearings and the overhead valves were enclosed in an aluminum casing atop the twin-port cast-iron head.
Exposed Valve Springs
Only the massive hairpin valve springs were exposed to the air Â– and these were rapidly replaced by coil springs with an ingenious means of taking up the valve clearances by eccentrics accessible from the exterior. To emphasize the relationship with the racing NSU "Bullus", the pushrods were enclosed in a tube designed to look like a racing overhead camshaft housing. The touring aspect resided in the enclosed chaincase lubricated by oil mist from the engine.
Engine: air-cooled 494cc (80x99mm) single-cylinder four-stroke
Power Rating: 22hp @ 5000rpm
Valves: overhead, hairpin springs
Fuel System: carburetor
Transmission: 3 speed foot change; primary and secondary chaincases
Suspension: girder forks (front); rigid (rear)
Brakes: 6.25in offset drums (front/rear)
Weight: 409 lb
Maximum Speed: 75 mph
Typical German motorcycles of the 1930s, the OSL series was particularly well made and remained in production until shortly after World War II.