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ESO motorcycles were designed by engineer Jaroslav Simandl and built in the Czechoslovakian Jawa/CZ factory. Though the engine was originally designed by Simandl for speedway (and was an exact copy of a British JAP), Simandl designed the S45 motocross engine (named for its actual horsepower output) on the then-new unit construction concept in 1957. Three ESO motors were available: 250cc, 350cc, and 500cc. All were dry sump (using an external oil tank) and fitted with four-speed transmissions. Among the most unique features of this engine design were the straight-cut gears and the backwards-spinning crankshaft.
ESO’s were always limited-production machines that ended up in the hands of the best club racers and GP riders. In typical Czech fashion, the ESO came with a complete spares kit that included spare engine, clutch and carburetor components. The ESO was taller, longer, and heavier than many of the British four-strokes of the era, but fast for the times. However, with the long chassis, heavy gross weight and slack head angle, it was a slow responder. Better find a berm!
The engines were so well regarded that Swede Sten Lundin used an ESO engine in a Lito frame to win the 1961 World Championship, while fellow World Champion Bill Nilsson stuffed an ESO engine into a Rickman Metisse in ’64. With a better chassis, the Czechoslovakian handling problems disappeared.
Unfortunately, the communist government commissars felt that the ESO was competing too well against CZ, and by the end of the 1964 season ESO was discontinued as a brand and absorbed into the Jawa factory.
WHAT THEY COST
This beautiful example was restored by well-known restorer Eldon Blasco and now belongs to the private Early Years Of Motocross Museum. Value is estimated at over $20,000. Restorable examples, if you can find them, will still cost more than $10,000.
250cc, 350cc, and 500cc motocross versions.
WHAT TO LOOK FOR
Pay attention to the detailing. A true ESO has lots of chrome bits and hand crafting. There is pin striping on the fenders, tank and rims.
Call Bertus CZ/Jawa in La Puente, California, at (626) 330-2326.
For more info on classic bikes go to www.earlyyearsofmx.com