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Built after the English school


Yamaha XS650

It is not only English motorcycle manufacturers who have used parallel twin engines. Yamaha, Laverda and Kawasaki have used this engine type. Yes, even Honda built small parallel twins of up to 400 cubic.


On a large engine over 500cc, vibration can be tamed with a balance shaft, and that's what some Japanese manufacturers chose to do to tame the beast, with more or less success.


The Japanese Bonneville

Some of the Japanese motorcycles that were built after the English school were the Yamaha XS 650 and the Kawasaki Z750. Yamaha built fine two-stroke machines, but understood that both American and European motorcyclists liked big, torquey machines with 4-stroke engines. Therefore, in 1969 they launched a motorcycle which was a Japanese counterpart to a Triumph Bonneville from that time. So it is no wonder that the XS 650 was called the Japanese Bonneville. It was an incredibly beautiful motorcycle and with a modern overhead camshaft engine. Over time, the model also got a self-starter. Just starting an English or American motorcycle from that time could be quite a challenge. A kind of ritual reminiscent of when Egon Olsen had to open a safe.


Good starting point, better over the years

Now the self-starter on an XS 650 was probably nothing to brag about, but the engine was. Yamaha chose to assemble the engine horizontally instead of vertically, and, among other reasons, the engine did not waste oil. The bearings were either roller or needle bearings, but in other words, a much better engine. Carburetors, charging and ignition systems in the Japanese motorcycles were also just a notch better.


The driving characteristics of the Japanese machines were, on the other hand, worse than on equivalent European machines. The combination of poor suspension and a small frame gave the first years quite poor driving characteristics. This was rectified somewhat with the updated B model in 1972. The XSII was a completely different machine to drive, and with disc brakes it was well ahead on that front too. The model even got 2 discs in the front over time and ended up being able to brake properly as well.


Yamaha hired Englishman Percy Tait, who had helped develop and refine Triumph's motorcycles, both on and off the racetrack. The B model of the XS 650 got a reinforced frame and a steeper head tube angle. But despite the help from Percy, the model never quite reached European level. Some suspension elements from the Italian motorcycle industry could have done wonders.


The model was in production until 1983 and was gradually developed to become a fine and harmonious machine. More than 500,000 units were thus produced. of all variants including the in my opinion dodgy Custom versions that certainly did nothing good for an otherwise fine motorcycle. One thing that followed the model from cradle to grave was the absolutely fantastic twin sound, which gave the model status even in Harley circles.


Something about the engine

On a motorcycle you are in close contact with the engine in a more direct way than in a car. After all, you sit on top of the engine, and all sounds and vibrations are conveyed directly to the driver. Weight and dimensions in relation to performance are decisive for how well an engine works in a motorcycle.


That is why most motorcycle engines are both light and high-performance. Many configurations have been tried ranging from 1 cylinder to 8 cylinders and even wobble engine. In fact, a 350 or 500cc engine can provide enough power for regular use in a street bike, and 1 cylinder is really enough. Back in the day, it was such engines that were the driving source in most motorcycles.


When 1 cylinder is too few and 4 are too many

When this was not enough, 2 cylinders placed next to each other was the solution. It was Triumph who started using what we know today as the traditional parallel twin (360 degree crank). This means that stamps are probably followed up and down. The advantage of this engine configuration is that the power pulses are in step, which makes for a nice engine sound, and it is an engine that is easy to manufacture and maintain. The disadvantages are vibrations.


Therefore, several modern parallel twins are made with 270 degree crank offset. Unfortunately, this not only eliminates the vibrations, but also the nice engine sound and quiet idling. A "real" parallel twin with a long stroke can pull completely from very low revs. Therefore, this engine type is more about torque than hp. High revs in search of power is not necessary. Therefore, the need for cooling is also limited, so water cooling is not necessary to keep the engine temperature in check.


The engine concept that went out of fashion

For many years, virtually all large motorcycles from England were parallel twins. And a large motorcycle back then was something like 500, 650 or 750 cubic meters. For many, a real motorcycle was a BSA, Triumph or Norton with such an engine. Matchless and Ariel also built fine machines with this engine type.

650 cubic meters and 50 hp were enough to reach the magical 100 mph or 160 km/h. Unfortunately, all these machines were built on technology from the 50s, and perhaps that is precisely why this engine type went out of fashion in the 70s.

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