T135 Development Story(Engine Design)

The power unit mounted on the T135 is a completely new liquid-cooled 4-stroke 135cc single-cylinder engine. It is the first liquid-cooled engine ever mounted on a Yamaha moped. Tatsuya Masuda, who headed the engine design project team says, "We wanted an engine that would run strongly at high rpm in the countryside and be easy to use in slower mid- to low-speed range riding in the city." He goes on to say, "We also wanted it to be an engine that ran quietly and was very reliable. And to do this we spent an especially large amount of time and energy working out that most important spec for determining the character of an engine: its bore x stroke." The T135 adopts a liquid cooling system and an array of state-of-the-art technologies like Yamaha's DiASil cylinder and forged piston. But it was this bore x stroke that consumed much of Masuda’s efforts. It was with this spec that he sought to give the engine a truly Yamaha character.

"If you get this basic spec right, you can do a lot of things later to fine-tune the engine," says Mr. Masuda. It was around October of last year after a series of road tests in Thailand that Masuda was finally convinced they had the right bore x stroke spec. Project Leader Kuromoto looks back on that time: "When I saw Masuda in the hotel lobby after those test were over, there were tears in his eyes. He had gone to Thailand with the motorcycle himself to see how close it was to the image he had been working toward and I guess he was really pleased. That's how difficult the task he had been given with the T135 engine was: to get both low- to mid-speed ease of use and good power at high speeds."

"I was confident that I had chosen the right spec," says Masuda, "but I guess I still had some doubts going into the tests, and it wasn't until the results were in that I was 100% sure we had the right basic engine to build on. ”Laughing, he went on to say, “It was such a relief that I just couldn't hold back the tears. Crying like that was something I didn’t even do when my first child was born."