3シリンダー TZ３５０

その後、ヤマハモーターNVと契約した片山は、新開発の3気筒エンジンと従来の2気筒エンジンの2種類のTZ350をサーキットによって使い分け、見事日本人初となるWGP350ccクラスのチャンピオンとなる。（記事の抜粋と画像はWikipediaから転載）

そういえば、シリンダー増設のことを聞いたのはこれが最初だったかもしれない。

The first person to create a 3 cylinders based on a Yamaha engine is Rudi Kurth, a racing sidecarist known for his engineering talents.  Kurth start working on his project in 1975 and mount a 3 cylinders 500 Yamaha on his monocoque sidecar.  This engine is based on the 350 TZ and is, in fact, one half of a 350 'welded' on the left side of a complete 350 TZ and shortening the stroke from 64mm to 51.8mm to get the 499cc.  Here is the TZ and half.  His sidecar is quick but Rudi Kurth is better engineer than pilot and he does not often see the end of a race, unfortunately.  Two Dutch mechanics specialized in Yamaha, Ferry Brouwer and Jerry Van der Heiden, study the project of Rudi Kurth with Minoru Tanaka, Department Technical Chief of Yamaha NV, the European bureau of the Japanese bike manufacturer.  Tanaka and Brouwer are two friends since the time they were the mechanics of Phil Read and Bill Ivy.

In 1975, they decide to pay a visit to Rudi Kurth, in Switzerland.  Then, a bit later, a 500 3 cylinders is prepared in the workshop of Tom Van Heugten, the sidecar cross champion who is a bike dealer.  The engine develop roughly 90HP and it is mounted in a TZ350 frame, the third cylinder out of line on the left side of the bike.

To bring this project from the National plan to the International one, the Grand Prix, a technical and financial help is needed.  It is Kunamotio San from Yamaha NV who start this European challenge.  Kent Anderson, the ex-world champion in 125cc is named chief of the project; Trevor Tilbury, young South-African mechanic join the team with Tanaka and Rudi Kurth.  Later, Tilbury will work for the Kenny Roberts team.
During the 1976 - 1977 winter, the work is hard in Holland, in Sweden and in Switzerland to be able to start the first Grand Prix as well prepared as possible.  The German firm Hoeckle is manufacturing the crankshaft at 120º, and Krober supply the ignition system.  This 350 3 cylinders is based on the 250cc TZ, with a third cylinder welded on its left side.（ttp://www.motopaedia.com/Bikes/yamaha_350_3_cylinders.htmより記事の抜粋と画像を転載）

とまあ、新開発の3気筒エンジンはヤマハ本社ではなくヨーロッパで作られたのだが、最初のアイディアはサイドカークロスにあったわけで、左側にクランクケースを溶接し120°クランクは新たに作ったとある。