Engineering was reluctant first
Shiro Nakamura (later also responsible for XS 750 triple, XS 400 twin, XS 1100 four and the SR 500) who developed the XT engine remembers: "When the off road market started booming in the US, bikers remembered the advantages of the good old singles.
Soon the sales guys started to request the development of a four stroke for off road. Honestly speaking, we engineers were quite reluctant in the beginning, since we knew about the difficulties of these big thumpers. As soon as they had a bit more power they turned out to be unreliable and they were shaking like hell."

Nakamura-san continues, "Now I can confess that developing this first big single was a real nightmare. It was only the second four-stroke designed by Yamaha. We tested many different configurations including DOHC and even cylinder head oil cooling, but the XT was supposed to be simple and reliable and eventually we turned away from all these complicated solutions."

Many technical problems to be solved
"First, the heavy pistons gave us countless problems. They seized up and were punched. Cylinder and head development was as difficult. We even had a cylinder that broke in the middle.
At that time we didn't even try balancer systems, although we had many problems with broken crankshaft bearings as well.
The con-rod had no big end bearing but was turning on a needle bearing that needed a low pressure lubrication. We did make this choice instead of using a one-piece forged crankshaft with assembled connecting rod because it allowed us to build a much more compact engine and was also cheaper to produce due to its vertically split crankcase."

"In the end all our technical problems delayed the roll out by more than one year. But we had succeeded, XT was now more reliable than a big single 4-stroke had ever been! Although it was over-square with a bore and stroke of 87 x 84 mm, (all British bikes were long stroke), we obtained the real character of a big thumper. The two-valve head gave a flat torque curve while the smaller flywheel allowed the engine to rev up as easily as we wanted. Dry sump and short stroke also allowed for better ground clearance and a more compact engine than former British bikes ever had."

Rollout in 1975 in US
The first XT 500 was shown at the US dealer convention in September 1975. Europeans had to wait till the summer of 1976 before they could press their boots against the heavy kick-starter.

The XT 500 was an instant success and was produced until 1990. It laid the ground for the later range of XT bikes ranging from 125 cc (XT 125) to 750 cc (XTZ 750) and contributed largely to Yamaha's image.

The XT proved it's performance and reliability by winning the first big African rallies, which were on the rise in the late seventies. It started with Paris-Abidjan-Nice and then the godfather of all rallies, the famous Paris-Dakar, which confirmed the supremacy of the XT 500. In France alone, 62.000 XT 500's were sold from 1976 to 1990.

SR 500: the thumper for open road
Shunji Tanaka's idea from the beginning of the XT project, was to develop a street model on the same engine base for the European market. He faced resistance first from marketing people, who were convinced that the big thumper era on the road was definitely dead. "We will only sell some units" he used to hear. Tanaka believed in his intuition and pushed the SR 500 thorough for the launch in the Japanese market in 1978.
While for the XT the priority had been reliability and simplicity, the keyword for this street model was "easy to use". The major difference between the SR and XT engine was the electronic ignition and a clever new concept to make kick start easier: an automatic decompressor system.

Nakamura tells a nice background story behind this: "It came in fact from an accident! Mr. Morinaga, Yamaha Motor's Technical Director, tested the SR prototype and got a wrench to his ankle as he tried to kick it. Easy starting then instantly became a first priority!"

 

British design influence
The SR 500 was designed by Atsushi Ishiyama, today President of GK dynamics.
He worked on the very first Yamaha's and contributed a lot to create Yamaha's reputation in design. He says: "Our choice was to design the new SR 500 with a strong family image and a strong link to our first four stroke, the XS 650 twin, which was also inspired by British design at first."

The SR 500 was going to become a legend as one of most reliable and easy-to-maintain motorcycles ever built. It sold until 1999, with a huge demand in Germany and Japan, until new noise and emission regulations signalled the end for the this big air-cooled single.

The XT 500 in the Paris Dakar rally
XT 500 enters desert Rallies in 1976 in the second edition of the first rally of this type organised, the "Paris-Abidjan-Nice" also called "Côte d'Ivoire-Côte d'Azur".
Four official XT were at the start on December 29th 1976. Completely standard with the exception of a 25 liter fuel tank and a sturdy luggage carrier supporting tools and two 5 litre jerry cans. Aside those machines engaged by the French importer, were 14 other XT's.

It was a fantastic success, a total of 10 XT finished this hard endurance desert race were Gilles Comte took the victory. For years the XT and Paris-Dakar Rally were words that belonged together. In 1979 and 1980, Cyril Neveu won on an XT 500.