YAMAHA YZ623 125cc!

Updated: Feb 16

Text: Ferry Brouwer

Photos: Facebook / Ferry Brouwer

1972, YZ623C

Yamaha had decided to withdraw completely from GP racing at the end of 1968.

Great was the surprise that for the 1969 season Yamaha presented a race bike based on the AS1 street bike, that was the YZ623.

Yamaha Motor NV got three which were distributed as follows, Kent Andersson, Jean Aureal (Sonauto) and Lous van Rijswijk (Motorpaleis Riemersma Racing Team).

For the Spanish GP, the first of the 1969 season, Kent Andersson lent his YZ623 to Spanish rider Salvador Cañellas.

1969, YZ623, from top to bottom and left to right: detail of the engine, Jean Aurial, Salvador Cañellas (GP of Spain / Jarama), Kent Andersson, Jean Aurial again and finally the Kent Andersson bike

The third (French) GP was a hit, Jean Aurial won his home GP.

Lous van Rijswijk finished tenth in the TT of Assen.

This must have inspired Yamaha to go further.

For the 1971 season, there was that new, much-changed YZ623A.

Yamaha Motor NV supported riders Kent Andersson and Rod Gould were to race these machines.

YAMAHA's achievements in the 125cc GP class in the 60s/70s

Rodney Gould wasn't too keen on riding a 125cc, so for the Isle of Man TT, Chas Mortimer was invited to ride the YZ623A (base AS3 with 6-speed gearbox).

That was a good choice because he immediately won the 125cc Isle of Man TT.

Therefore, Chas Mortimer took part in the remainder of the season in the place of Rodney Gould.

Mortimer finished fifth and Andersson ninth in the 125cc World Championship.

For the 1972 season, Andersson and Mortimer showed-up with improved machines, which was the YZ623C.

1971, YZ623A, top to bottom and left to right: two photos of the bike, Chas Mortimer ahead of Barry Sheene (SUZUKI) in the Isle of Man and the Austrian GP, Rodney Gould leading ahead of Ángel Nieto (DERBI )

From air-cooled to water-cooled, and bore x stroke from 43x43 to 44x41 increased.

During the year a new developed dryclutch, and also the power had increased.

Mortimer again won the 125cc TT on the Isle of Man, and Andersson won three GPs.

They finished second and third in the 125cc World Championship.

For the 1973 season it was only Kent Andersson with Yamaha Motor NV support, he went into the season with a YZ623C he had improved himself with help of Engineer Naito san at YMNV.

1972, top to bottom and left to right: the YZ623C, Chas Mortimer and Kent Andersson

Mortimer was to keep his 1972 YZ623C.

Andersson won five GPs, Tommy Robb on Mortimer's machine the TT on the Isle of Man, and Mortimer the last GP in Spain.

Kent Andersson became 125cc World Champion and Chas Mortimer second. not bad for an engine still based on an AS3.

Then 50 years ago came the 1974 season brand new YZR125 0W15 machines for Kent Anderson and new man Bruno Kneubühler.

The engine showed again improved horsepower, but the basis of the machine was actually still the same as the YZ623C.

YAMAHA AS1-D, 1967, the origin of success!

Kent again won the 125cc World Championship, teammate Bruno Kneubühler was second.

It turned out to be the very last 125cc World Championship for Kent Andersson and Yamaha.

Yamaha became Manufacturers World Champion in the 125cc / 250cc / 350cc / 500cc that year.

Kent and Bruno continued on a private basis in 1975 with their 0W15s with which Kent won the first GP, Bruno the Dutch TT, and Leif Gustafsson on the 1973 YZ623C of Kent won the last GP.

Kent finished third, Leif fourth and Bruno sixth in the 1975 World Championship.

Kent Andersson and the YZ623C became Yamaha's most successful 125cc rider and machine an era had come to an end.