50cc Roadracing 1966


In the 50 cc there was fierce competition between Taveri and Bryans on their Hondas, and Anscheidt, after the withdrawal of Kreidler, now on a Suzuki twin. After the one but last GP of the season, the Isle of Man TT (that year one but last because strikes in Great Britain prevented the TT from being held in June as usual), all three riders had 26 points, and a chance of the title. Then it became known, that the Japanese GP that year would not be held on the Honda owned Suzuka circuit, but on the new Fisco course, whereupon Honda decided not to participate, and the individual title went more or less by default to Anscheidt. However, the manufacturer's title went to Honda.


The 1966 RK66 engine had originally a twelve-speed gearbox, but on Anscheidt's advice, this was changed to a fourteen speeder. Power output of the RK66 was 16.5 bhp at 17,000 rpm. Compression ratio 8.5 : 1 and top speed was given as 172 km/h.


The machine used during 1966 was called the RC116. Difference between the RC115 and the RC116 was a new bore and stroke, being 35.5 x 25.14 mm. Power output was 16 bhp at 21,500 rpm. At the rear wheel! This means 320 bhp per litre and a Pme of nearly 16 kg/cm2! As regards bhp per litre, this is a figure that has never been surpassed by any naturally aspirated four-stroke engine, and even today's Formula 1 cars with their special fuel brews cannot hold a candle to it. I know this is not a totally fair comparison, but it gives an idea of the level of four-stroke technology 40 years ago. This engine was the most advanced of all the Honda engines. Red line at 22,500 rpm. Carburettors had flat slides. The gearbox contained a nine-speed cluster. Dry weight of the bike was 58 kg. The piston pin had a diameter of 9 mm and weighed 6 g. The inlet valve head was 13 mm, the exhaust valve head was 11.5 mm, and the stems had a diameter of 3.5 mm. Weight of the exhaust valve: 6 g. At the end of the 1966 season, Honda withdrew from 50 cc racing.


Nothing new about the 1966 Derbi is known.


A newcomer from Japan that year was Bridgestone, the well known tyre manufacturer. They showed up for the first time at the Dutch TT of Assen, under riders Morishita and Jack Findlay, who finished 6th and 8th respectively. (See pic. Bridgestone). Only thing known about them is that they were two-strokes with rotating inlets.


1966 was the year the Dutch Jamathi made its debut during the Dutch TT, finishing in ninth place. The men responsible for the bike were Jan Thiel and Martin Mijwaart, hence the name. The rider was normally Paul Lodewijkx, who, when not racing, helped out in the "factory" However, during the 1966 TT it was Mijwaart who raced the Jamathi. See pic. Jamathi2. F.l.t.r.: Jan Thiel, Paul Lodewijkx and Martin Mijwaart. The home-built frame looks a bit like the Suzuki one. Front forks and brakes were own constructions. Tyre sizes front/rear: 18 x 2.00 and 18 x 2.25. Total weight 49 kg, top speed 150 km/h.
The engine was a single cylinder, air-cooled two-stroke. The cylinder had three transfer ports like the MZ. Bore and stroke 40 x 39.5 mm. The piston had one piston ring, from a Suzuki. Lubrication by oil/petrol mixture 1 : 15. Geometric compression ratio 16 : 1. Carburation by 24 mm Dell'Orto. The crankshaft carter was bolted to the housing of the nine-speed gearbox.

Listen !

Watch the start of the Assen TT !