The following article was kindly forwarded to me by John Blackburn and originated from the Czech Motor Review of 1956.

Motor Manafacturers consider the race course the best test bench for their products. In no laboratory can conditions be adjusted so as to correspond to the endless variety which rider and machine meet on the racing track. Only there can the engine, and indeed the whole machine be subjected to the most severe "breaking test" at which every part undergoes the maximum stress both in respect of performance and reliability. If this experience applies to the manafacturers of standard vehicles, naturally it has to become law for vehicles intended exclusively to be used in sporting events. These vehicles come into the hands of drivers who can never attempt to spare the engine or the vehicle as a whole. They endeavour to achieve all the success and consequently, make full use of the engine output and of the road qaulities of the machine. If it is taken into account that some riders cannot be relied upon to service their machines correctly and with the care which only many years of experience and expert knowledge of servicing can assure, then it will be realised that the manafacturer of sports and and racing machines is thus getting into an awkward situation. In contrast to touring machines, in this case all of his vehicles are subjected to hard tests without the certainty of expert servicing.

In view of these experiences, the ESO Works are endeavouring to make use of all sporting events to gain fresh information, to the verify the present design and evidently also to search for new ways which the development of ESO engines and motorcycles should in future take. Let us have a look what reflection these experiences have on the design and modifications which we will meet on the ESO speedway motorcycles in the course of racing next season.

Since 1952 when the new ESO engine model S45 was created, it became obvious that the design is successful and that it fulfilled all expectations already in the first phase of its development. The best proof is in the six times repeated win of H.Roasak in the Championship of Czechoslovakia (1952-1956), the uninterupted sequence of which bears evidence not only of the speed, but also of the reliability of the ESO engines and motorcycles. Although the ESO engines were originally designed for the classic speedway, i.e for tracks 300 to 400 m long, on which the reliabilty of the engine was convincingly shown, its crankshaft assembly has been redesigned to enable the engine being used also, on the longest tracks and at the same time, its reliabilty increased for short distances. The main bearing of the crank pin on the drive side was enlarged so that one row of rollers was shifted as near as possible to the engine sprocket. The rigidity of the crankshaft assembly was further increased by renforcing the connecting rod pin which besides this is provided with a hard ring of special material. The connecting rod is now supported on two rows, in all, 24 rollers.

Much attention was devoted to the connecting rod which is now of an entirely new shape. Enlarged fins go now round both the small and big end and ensure the rigidity of the connecting rod also at long term maximum loads. The top of the piston was redesigned for the same reason. The new engines are provided with special scraper rings, 1.5mm wide. In 1957, new ESO carburettors will be fitted, which due to their internal arrangement will ensure maximum output with smooth passages at all revolutions of the engine. The outer arrangement, a single casting of the carburettor body with float chamber will eliminate the frequent defects of the seperate design and so increase the reliability of the machine.

There certain modifications originating so to speak direct from the racing track on the cycle part of the ESO as well. The most substantial is a new design of telescopic front fork giving good handling to the motorcycle also at high speeds over long courses with bad surface and improved riding qaulities over classic short tracks. The frame was redisgned so as to make the lowering of the saddle possible. The engine and the Gearbox have been shifted rearwards so that the chain is now shorter, reducing the risk of its falling off. ESO speedway motorcycles have been supplied up until now exclusively with two speed gearboxes. In 1957, the machine can be equpped either with thisgearbox or with a layshaft to suit the wishes of the rider. The fuel tank will in future be supported on rubber so that it will not suffer from the shocks and vibrations of the machine. The speed and reliability of the ESO speedway machine drew attention also of foreign riders, many of whom are now riding these machines. Of the best known are K.Killmeyer, Kupczinski, Anderson, Siegi, Seemander, Craighead and Bishop must be mentioned.

Even the World Champion Fundin was interested in the ESO which is best shown by the incident during the match between the Swedish club Kapama, Fylbirterna and the Polish Club Sparta Wroclaw. For this event, three ESO machines were lent, but did not arrive until just before the race so that riders were unable to get acquainted with them during practice. Therefore, the Polish manager decided that it would be too much of a risk to engage in such a difficult event on new motorcycles, and only when the Swedish club was leading with a great difference of points did he allow the best riders, Champion of Poland Szwendrowski and ex-champion Kupczinski to try the ESO machines. To the great amazement of both spectators and riders, these two competitors were from then on taking first places so that the score of the Polish club improved considerably before the end of the event.

Even Fundin was surprised by the performance of the ESO and he asked through the Intermediary of the manager of the Swedish club Mr Jacobson that the third machine should be lent to him to try it out. Everybody expected that Fundin would first ride a few laps as a trial, but he rode to the starting line and obviously was waiting for the other competitors. Kupczinski Szwendrowski and one of the Swedish riders, therefore quickly started their machines and joined Fundin. Although Fundin left the starting gate last, he overtook both rivals on the second bend on the outside and was all the time increasing his advantage to the finish line. Having arrived at the pits, he declared "I have not had such a good engine before".

The success of the S45 engine in speedway leads naturally to the attempt to widen the use of this engine to other branches of the motorcycle sport. The result of these endeavours were the new models of engines, the ESO 350 and 500B which were throughout this years season tried out in prototypes of ESO scramblers. It appeared that these engines assert themselves excellently also at moto-cross races. In both cases, the S45 engine is designed in unit with a four speed gearbox (even the 350cc engine keeps the over sqaure design: bore 80mm x stroke 69mm). The engine and the gearbox are connected and lubricated by a single dry-sump lubricating system (double piston type pump) so that the gearbox losses are reduced to a minimum, and a very short construction and low weight of the engine is achieved. The primary drive (1.88 to 1)is by gears, the clutch is dry, multiplate). The prototypes of the ESO moto cross motorcycles have proved themselves so well in this years season both at home and abroad, that they are going into production for the next season with a modification based on the experience in that season.

At first sight, the motorcycle strikes with its simple and purely functional construction. The simple frame is reinforced with the oil tank (capacity 4 Litres) which forms one of its carrying parts and into which the air cleaner of the carburettor has been built to admit the air high under the saddle. The front fork is telescopic with hydraulic damping and hydraulic stops whilst the rear suspension is by pivoted fork with its centre of rotation placed as near as possible to the gearbox sprocket. The full width hub brakes are of 180mm diameter and have 35mm lining. The saddle is hinged sideways and gives access to the oil tank filler neck. The wheels are equpped with special scramble type tyres of 3.00 - 21 size at front and 4.00 - 19 at the rear. Other data are shown in the following table.

Weight: 282lbs (128kg)
Wheel Base: 55.5ins (1410mm)
Overall Length: 83in (2,110mm)
Ground Clearance: 7.7ins (195mm)
Saddle Height: 32in (815mm)
Handlebars: 29in (740mm)
Fuel: 80 Octane Petrol

A 250cc engine of similar design is being prepared, so that in the 1957 season, ESO motorcycles of all three classes will be available.