| Yamaha 125 cc Factory Racers |
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The development story of the 125 ccm Yamaha Factory machines is very interesting as it started out with very simple machines. The first 125 cc "racer" was a "tuned" version of the standard YA1, the "Red Dragonfly" I have to search of course for pictures of the missing models, but they will be added later. Here is a list with all the real "Works" machines and their codes: (Please note that the YA1 was a simple "tuned" standard production machine, used for a "primitive" form of racing)
The first really built for racing bike was the Works Asama 125 cc racer for 1957. A very special story will be made of these very early machines. The picture is from the start at the actual Mount Asama race in 1957!
The Yamaha RA41 G.P. machine was the first works racer built to race on the European G.P. circuits. The prototype was called YX41, a single cylinder engine with 2 rotary valves, which was used during the mid '61/end '62 period.
Yamaha RA41 1961
The machine specifications also included the already famous Yamaha Autolube Sytem (you can see the pump on top of the crankcase). Even one of the two carburettors can be seen.
By the end of 1962 the RA55 replaced the RA41 (November 1962) shortly as it was more a testbed for the RD56 twin 250 ccm racer to come.
Yamaha RA55 1962
The 1963 racer was named the RA75. It had an 8-speed gearbox and was used quite extensively. It was still a single, breathing through 2 big Mikuni M34 carburettors (again 2 rotary valves).
Yamaha RA75 1963
Here are some details of the RA75
Yamaha RA75 1963
The RA97 arrived on the circuits by mid 1964, preceded by the experimental YX97 machine. This new twin cylinder bike had a bore/stroke of 44 x 41 mm, a dimension which Yamaha would abandon later but after much consideration re-used in 1972. The first “generation” of the RA97 was air-cooled. 
Yamaha RA97 1964
From the details the relatively wide construction of the rotary valve engine can be seen, including the “bulbeous” cowling that also was fitted to the later 250 cc machines.
Yamaha RA97 1964
The second version of the Yamaha RA97 of early 1965 was already water-cooled. The intricate “plumbing” of the little machine can be clearly seen here.
Yamaha RA97 1965
Yamaha Japan still has one of these beauties in their collection.
Yamaha RA97 1965
The last RA97 is practically identical, the clutch was improved and power was slightly up.
Yamaha RA97 1966
Also the tachometer drive got a different place.
Yamaha RA97 1966
By the end of 1966 the fantastic V-Four RA31 was introduced. The first machine had very similar power to the latest RA97, but this was quickly “pumped-up” to 40 PS.
Yamaha RA31/A 1967
The RA31 was followed by the Yamaha RA31A, ultimately with 44 PS at 17.300 rpm.
When the Japanese factories pulled out of G.P. Roadracing by the end of 1968, Yamaha wished to continue anyway in some form. It was decided to build small series of machines utilizing standard components and some “special” bits. The first machine was the YZ623, actually a TA125 prototype (which arrived only in 1973). The YZ623 was (at first) based upon the AS1 “GYT” kitted racer and given to Yamaha Importer selected riders. The Dutch Yamaha Distributor got a few for the just founded MRTN team (Motor Racing Team Netherlands).
Yamaha YZ623 1969
The details show the (later) TA125 similarity with the DS6 front brake/CS5 backplate.
Yamaha YZ623 1969
Cees van Dongen, the Dutch Importer’s chief mechanic, converted the AS1 based racer su much that it bore striking resemblance with the YZ623.He had quite some success with it.
The Autolube pump drive was used to drive the tachometer.
Yamaha AS1/3 YZ623 copy 1969
In 1971 the YZ623A arrived, now based upon the AS3 engine and much stronger/faster. This was the machine taken by the late Kent Andersson for further development. Pictures follow.
The YZ623A was air cooled and many of the private riders were already converting their machines to water cooling as you can have seen in the story about the 125 cc production based racers. Kent Andersson converted the engine as well and Yamaha responded by fitting a beautiful water cooled conversion to the 1972 YZ623C model. This is Chas Mortimer's machine, he used right hand gear change. The first YZ623C machines still had a wet clutch as you can see.
Yamaha YZ623C 1972
Another proof of the bike being Chas Mortime's mount! The rear brake is on the left!
Yamaha YZ623C 1972
The second lot of YZ623C racers arrived a few months later and were photographed here in front of the Amsterdam garage of my boss, Mr. Ishibashi. Imagine that today, parking works machines in a normal garage in the city!. 
Yamaha YZ623C 1972
Pure coincidence, again the machine for Chas Mortimer. Riders were now sponsored by European Yamaha Distributors and Chas had DANFAY Distributors (Ireland) as back-up.
Yamaha YZ623C 1972
Kent Andersson’s World Championship winning machine of the 1974 season has a proud place in the Yamaha collection.
Yamaha OW15 1974
You will agree that this is how a motorcycle should look !
Yamaha OW15 1974
1975 was the last year Kent Andersson rode the OW15, the ultimate version, now also equipped with disc brakes on the front. You see Kent just above the fueltank, talking with Harold Bartol, the equally famous Austrian tuner/engineer. Kent Andersson was the only rider who rode all Yamaha factory twin cylinder 125 cc racers between 1969 - 1975!
Yamaha OW15 1975
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