1959 ESO 500 SCRAMBLER:
BLACK SWAN OR UGLY DUCKLING?
ESO motorcycles were designed by engineer Jaroslav Simandl and built in the Czechoslovakia 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 engines were available: 250cc, 350cc, and
BY TOM WHITE
500cc. All were dry sump (using an external oil tank) and
fitted with four-speed transmissions. The most unique
features of this engine design were the straight-cut gears
and the backwards-spinning crankshaft.
ESOs 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 engine, clutch and