The ESO Road Racers
Wednesday, May 16th, 2007Jaroslav Simandl was the owner of a small engineering firm in post war Czechoslovakia, he was also a speedway rider, so naturally enough he found himself making replacement parts for his JAP powered machine because foreign currency was not available in the Eastern bloc to enable import of much needed spares. He was soon supplying other riders
with them.
By 1949 he was making complete replica JAP speedway machines, soon with “ESO” (Czecho for “Ace”) on rocker box and tank. (Although “JAP” was still on the cover at the bottom of the timing side crankcase)
In 1950 his son Jiri took up road racing so they built several machines using their JAPclone engines, 4 speed boxes and telescopic-forks. They also used their own twin loop swingarm frame, proving that it was not only the McCandless brothers who were looking to improve handling with better frames. In fact, Simandl made the move before Nortons
did.
So successful were the ESO/JAP speedway engines, and the 5 road racers, that a new factory was soon established in Divisov.
During 1953 they released the short stroke 88mm x 82mm S45, the first fully ESO designed engine. (Later rebadged as JAWA) So well designed and conceived was this engine that the improvements and changes over its 30+ year production life were minor. The only major reliability improvement was to the crankpin in about 1966, it changed from a nutted taper to a stepped parallel press fit construction. Similarly, all other improvements were “add-ins”.
They simply got this engine brilliantly ‘right’ … from the beginning!
In 1953-54 several of these engines were put into factory road racers, again using the separate ESO gearbox. Their 42bhp @ 7,500 rpm on petrol was the same as the Goldie achieved a few years later. Again, these bikes had a twin loop frame closely resembling the Featherbed that had just appeared in Britain, but now a trailing link front suspension and a 230mm SLS full width brake graced the front. This, with a 200mm hub on the rear meant that it stopped well, something only the Italians had woken up to by then.
What a pity those eastern bloc low budget factories found it impossible to compete on the world stage. However, the new ESO pushrod singles beat the entire works road race team with their Jawa DOHC 500 twins at the Czech championships in ’54
But just when things were looking rosy the ‘government’ got in the way, as they had a habit of doing in Eastern Europe back then. The speedway engines had become so successful that Simandl’s company was ordered to concentrate on speedway machines and to leave the road racing to Jawa, who already had world recognition in this class.
However, against the odds Simandl continued with the road racing development and by the end of 1954 he and his chief designer Jaroslav Cervinka had designed and produced a unit construction wet sumped engine that owed little to the speedway engine apart from the cylinder had and cylinder castings.
But the works Jawa DOHC twin had been redesigned by now and had found more speed and reliability, so perhaps the new engine was not quite the step they really needed?
So only eight 500s and five 350s were produced and successful as they were, these engines went on to be developed into the 1955 ESO motocross machines because Simandl now had other plans…
By 1957 they had an exciting DOHC 4 valve 5 speed unit construction model that produced 52hp at 9500rpm, which would have seen it quite competitive with the Manx at that time. Unfortunately they did not race it outside Czechoslovakia, so intent were they on producing the speedway engine and so doubtful that they could ever capitalize on it.
By 1966 the ‘government’ announced that the ESO speedway machines would henceforth be known and marketed as JAWA. The Jawa marque was by now well established in the west, it made no commercial sense to start and fund new distribution channels and dealerships so the companies were to merge, although the bikes were still made in the ESO factory. If you look under the skirt of every 2 valve Jawa piston you will find ”ESO”….and until the early 70s the ESO logo continued to bracket the engine numbers on Jawa crankcases.
In the late 70s, when the 2 valve ESO/Jawa’s reign was coming to the end with the appearance of 4 valve rivals, they turned again to Cervinka to design their own 4 valve machine, and that went on to win countless national and world titles, as had its 2 valve predecessor.
That success makes one wonder, what if Simandl had been allowed to continue with the Cervinka-designed 1957 unit 4 valve 5 speed DOHC road racing machines……… ?
One of the original 1950 bikes, a pre-unit S45 model and several unit machines are still raced in Europe, In addition there have been numerous speedway-engined road race specials built and raced the world over since the mid 50s…..and for those who think that there were no ESO specials raced here in Australia in the pre-1963 period, think again……both an AJS 7R-framed ESO raced in Tasmania and another ESO special raced in NSW in the early 60s.
Oh, and if you check out the timing side cover of all the pre-68 ESO/Jawa speedway engines you will note that the boss on which the rectangular-ish oil pump is mounted is round, to suit the round recirculating gear pumps that the factory road racers used. These engines still carried their joint road-racing heritage with them.
When you consider that specials formed the background of racing here in Australia during the 50s and for most of the 60s, the ESO specials certainly have a rightful place in the racing history and race tracks of Australia.
Greg Summerton