Yamaha 250 cc YA/B Asama racer

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It is quite amazing that because of all those new friends which I got through the website, so much very interesting items come-up. Here is the story of an early Yamaha racing motorcycle, that should not exist! It is unknown in Japan.....! The 1957 Asama 125 cc racer.

The YA Asama Works racer.

We really shouldn't forget this rare little machine, and it really was Yamaha's first 125 racer. This bike is one of the YA-B short stroke bikes. It was brought over to the U.S. around 1959 and raced at least once. It was broken up and discarded in a dumpster (probably ordered destroyed by Yamaha) but some kind hearted scavenger rescued most of it from extinction! Being here in the U.S. is probably why it survives. We believe the other 4 were destroyed by Yamaha as is the usual practice with Works bikes. It is almost certain the only surviving YA Works bike. You can clearly see it is a much different machine than the YA-1's, which were simply “tuned” street 125 cc bikes. And we also should not forget that this bike is more htan half a century old now and that most of the men who worked on it are deep in their eighties or not alive anymore. Even Japanese motorcycle history gets older!

(Five of these machines were produced for the Mt. Asama GP in 1957)

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Two specifications were made, a "square" engine and a "short stroke". The machine discussed here is the short stroke racer.

yr code cyl cool ind bxs hp/rpm ign clut carb sp
57 YA-A 1 air pist 54x54 14 mag wet aml27 4
57 YA-B 1 air pist 56x50 14 mag wet aml27 4

Yamaha YA-B 1957 racer
Yamaha YA-B 1957 racer

Cylinder, clutch and other gearbox parts. Gearbox has 4 speeds. The shifting mechanism was also used on later Yamaha's.

The exhaust pipe was also like that used later on by the RA41. The intake is fed into the engine cases and had a long intake manifold. The Amal GP 27mm carburettor was used with a remote float chamber. The magneto ignition was fitted on the r.h. crank case. Clutch is the same as on the YD 250 with square cut primary drive. Engine was over built and very robust. It developed 14 PS.

Yamaha YA-B 1957 racer
Yamaha YA-B 1957 racer

Crankcase halves and crankcase cover show similarities with the Yamaha Catalina racer 250 cc machine.

The bikes had fairings and rear set footrests. Clip-on handlebars and tachometers were also fitted.

Yamaha YA-B 1957 racer
Yamaha YA-B 1957 racer

Wheel hubs are also similar and the steering damper looks like it will fit a YDS1/2/3 already!

 

Yamaha YA-B 1957 racer
Yamaha YA-B 1957 racer

The cylinder head looks exactly like the one used on the later RA41.

Yamaha YA-B 1957 racer
Yamaha YA-B 1957 racer

The frame already has a nice double-loop construction, also a feature later seen on the production bikes.

Yamaha YA-B 1957 racer
Yamaha YA-B 1957 racer

Yamaha YA-B 1957 racer
Yamaha YA-B 1957 racer

Yamaha YA-B 1957 racer
Yamaha YA-B 1957 racer

 

The YA's were unbeatable at a very important time in Yamaha's history. The RA41 didn't have as much success. Here are some detailed close up pictures of the YA-B's engine cases. Note the crudeness of the castings! The number #1 is on the lower rear of the cases on the mounting lugs. We assume this indicates the very first set of cases machined! We are not sure what the S7 means.

Yamaha YA-B 1957 racer
Yamaha YA-B 1957 racer

Engine number of this rare machine is S30.

Yamaha YA-B 1957 racer
Yamaha YA-B 1957 racer

Interesting note is that the cylinder head is marked 7 in yellow paint. You can also see traces of yellow paint in the case stamping where it's stamped S7 A#. Again the 7 appears where the cases are stamped YA-B7.

Yamaha YA-B 1957 racer
Yamaha YA-B 1957 racer

Yamaha YA-B 1957 racer
Yamaha YA-B 1957 racer

Yamaha YA-B 1957 racer
Yamaha YA-B 1957 racer

Here is also a picture of the cylinder head bottom showing the "7" painted on. The head gasket must have been a recessed copper gasket as Yamaha later on used on the TR1-2-3 racers and the combustion chamber is highly polished as can be seen. The cylinder head has massive fins.

We think we have seen this "7" appear on other early works racers also. Maybe it was a way to identify the engine builder of a particular engine? If you study the YD 250 Asama racers closely you'll notice on their clutch covers a pattern painted on. Some had a square, some a circle, triangle, etc. Maybe it is another form to ID the bike to it's mechanic? Not a big deal but very interesting never the less.

On the Yamaha Communication Website the data for 1957 mentioned are wrong! They list the 1957 Asama winner as being a normal YA-1 and even worse, listed the lightweight(250) winners as being the YC1! It's pretty bad when the Yamaha Factory's own Museum Website is incorrect!

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