ESO

500 Motocross / Miloslav Soucek - 1959

End of an independent marque

Founded in 1949 at Divisov by a former speedway rider named Jaroslav Simandl, ESO began by manufacturing replacement parts for postwar JAP speedway engines.

From Speedway to Motocross

ESO was soon making complete engines (closely related to JAP engines) designed by and built under the supervision of Simandl. The later S45 engine owed nothing to the JAP, however. Designed for speedway racing, it had no gearbox. Then, since motocross was developing fast, Simandl began production of an extremely compact unit-construction engine in 250, 350 and 500cc capacities.

State Intervention

In contrast to speedway machines with their total-loss lubrication systems, ESO motocross bikes have dry-sump lubrication. Though they are powerful, they are handicapped by their strong – but heavy – frames. Most are built for local consumption, and very few are exported. In 1963, the factory concentrated its efforts on the 500cc class, and in 1964, the Swedish champion Bill Nilsson rode a works ESO with a British Metisse frame and finished fifth in the World Championship. The following year, he rode a "100 percent ESO," but a broken shoulder prevented him from finishing the season. ESO had missed its last chance of winning the Championship because the firm was nationalized in 1965 and passed into the control of Jawa. Subsequently, only speedway engines were sold under the ESO label since Czechoslovakia was only represented in motocross by the Jawa and CZ two-stroke bikes.

SPECIFICATIONS

Engine: 499cc (88x82mm) air-cooled single-cylinder four-stroke

Power Rating: 40 hp @ 6500 rpm

Valves: overhead

Fuel System: 35mm ESO or DellÂ’Orto carburetor

Transmission: 4-speed, chain final drive

Suspension: telescopic forks (front); swing arm (rear)

Brakes: drum (front & rear)

Wheels: 21 inch (front); 18 or 19 inch depending on year (rear)

Weight: 287 lb

Miloslav Soucek, top-scoring Czech four-stroke rider in the World Championship, waiting for the drop of the flag in a motocross meeting at Beauval-en-Caux (France) in 1962.