50cc Roadracing 1973


For the 1973 season, Derbi had withdrawn from Grand Prix racing, so the heat was on between Dutch Van Veen Kreidler and -Jamathi and Swedish Monark, which had retained the services of Jan Bruins as work's rider.

First race of the season was the German GP, where Jan de Vries (Van Veen Kreidler) initially led the race from team mate Bruno Kneubühler, who retired on lap 8 with a broken crankshaft. The same happened to De Vries in lap 10, which gave the victory to Theo Timmer (Jamathi), with 2. Henk van Kessel (Kreidler), 3. W. Gedlich (Kreidler), 4. H. Rittberger (Kreidler), 5. J. Röller (Kreidler), and 6. Jan Huberts (Kreidler).

Next race was Monza, where Jan de Vries (Van Veen Kreidler) won, 23 seconds ahead of his teammate Kneubühler. Third was Gerhard Thurow (Kreidler), with 4. Theo Timmer (Jamathi), 5. Jan Huberts (Kreidler) and 6. H. Graf (Kreidler).

In Opatija, Jugoslavia, De Vries won a race which was beset with mechanical troubles, which forced Jan Bruins (Monark), Bruno Kneubühler (Van Veen Kreidler) and Theo Timmer (Jamathi) out. Winner was De Vries (Van Veen Kreidler), followed by 2. U. Graf (Kreidler), 3. S. Dörflinger (Kreidler), 4. H. Bartol (Kreidler), 5. H. Rittberger (Kreidler) and 6. L. Persson (Monark).

During the Dutch TT, which so far seemed to have been destined hardly ever to see a Dutchman win, kept to its tradition: De Vries, leading the race, retired with a damaged conrod, and Kneubühler (Van Veen Kreidler) won the race, ahead of Timmer (Jamathi). Third was Thurow (Kreidler), with 4. Bruins (Monark), 5. Persson (Monark) and 6. Huberts (Kreidler).

In Francorchamps De Vries won with a new record fastest lap speed of 162.224 km/h, with 2. Kneubühler (Van Veen Kreidler), 3. Timmer (Jamathi), 4. Kunz (Kreidler), 5. Thurow (Kreidler) and 6. Huberts (Kreidler). Top speed of De Vries' Van Veen Kreidler was measured with 202 km/h!

Next was Sweden, where the sequence was 1. De Vries (Van Veen Kreidler), 2. Kneubühler (Van Veen Kreidler), 3. Timmer (Jamathi), 4. Thurow (Kreidler), 5. Kunz (Kreidler), and 6. Van Kessel (Kreidler). Bruins (Monark) retired. This result gave Jan de Vries the world title.

Last race of the season was Barcelona, and to make sure that the vice-world champion would be Kneubühler (Theo Timmer with the Jamathi still had a chance to come second in the championship), Van Veen gave fast engines to Jan Huberts and Henk van Kessel. The race ended with 1. De Vries (Van Veen Kreidler), 2. Kneubühler (Van Veen Kreidler), 3. Van Kessel (Kreidler), 4. Thurow (Kreidler), 5. Huberts (Kreidler) and 6. Timmer (Jamathi). Obviously Van Veen's ploy had worked.

The world championship was won by Jan de Vries (Van Veen Kreidler) with Bruno Kneubühler (Van Veen Kreidler) second and Theo Timmer (Jamathi) third.
J.Kortekaas 2006

The Bikes

Van Veen Kreidler

The Van Veen Kreidlers, now tuned by Ing. Jorg Möller, only differed in details from the ones used the previous year. They no longer had the forced lubrication with a pump, and returned to an elctrically driven water pump. Power 20 bhp.


The Jamathis retained the monocoque frame, but got a new engine. The radiator was mounted in the nose of the fairing, and this high position, combined with the low position of the horizontal cylinder, allowed the use of a thermosyphon system, i.e., a system without a water pump, whereby the water circulation relies totally on the differences in temperature.


Dutchman Jan Bruins, a succesful tuner, helped developing the 50 cc Monark racers. The cylinder and head got water cooling with an electrically driven pump, and the Gardner carburettor was replaced with a Bing. Furthermore the road holding was improved by using Marzocchi shock absorbers for the swing arm. At the beginning of the 1973 season the Monark had approximately the same power as the private Kreidler with which Bruins won the Yugoslavian GP in 1972. The bike still had the clutch running in the oil bath.


Derbi's retirement from Grand prix racing left Angel Nieto without a bike, but he was contracted by Morbidelli. However, the bikes must not have been competitive, because he never appeared in the results, and it was not even possible to find out whether he ever started.


Although Derbi didn't compete with a work's team, they brought out a production racer for sale to the general public. This had an air cooled engine with a rotating inlet, dry clutch and six-speed gearbox. The cylinder was a simple aluminium one with hard-chromium plated bore, and a simple three port system. This cylinder should be the first to go if real power was to be developed. Also the crankshaft should go: with a bore and stroke of 38 x 43 mm was the engine no longer to be taken seriously! Claimed power was 15.5 bhp at 15,000 rpm, figures which seem with a view to cylinder and bore/stroke ratio somewhat optimistic - compare it to the data of the Kreidler tuning kit below. Torque 0.73 mkg at 14,500 rpm. Spanish IRZ carburettor with 24 mm diameter. Ignition by breakerless Motoplat thyristor system. Gear ratios: 2.1 - 1.666 - 1.411 - 1.222 - 1.095 - 1 : 1. The frame was open on the underside. Front forks and shock absorbers from Spanish Ideal, Aluminium Akront rims with Spanish aluminium brakes (double 2ls front, looks like a Fontani imitation). Wheelbase 1226 mm, claimed top speed 165 km/h.


Probably inspired by the successes of the Van Veen Kreidlers, the Kreidler factory brought out a tuning kit for the RS engines. Water cooling for cylinder and head, special crankshaft with polished conrod and racing piston with one L-shaped piston ring, electrical water pump, 28 mm Bing carburettor. Guaranteed power 14.5 to 15 bhp at 14,500 rpm.