The Yamaha XS Eleven motorcycle, also called XS11 and XS1100, is a Japanese standard produced from 1977 (MY1978) to 1983, powered by an air-cooled 4-stroke, DOHC inline four-cylinder engine mounted transversely in a duplex cradle frame with swingarm rear suspension, shaft drive, and telescopic forks.
History & Technology
The XS Eleven was the first four-cylinder four-stroke motorcycle from Yamaha. It built on technology first used by Yamaha in their earlier XS 750 four-stroke triple. However, the XS 1100 engine design was in reality a completely new design with several relatively unconventional elements when compared to other inline 4-cylinder motorcycle engines of the day.
The "over-square" design of the XS 1100 engine (Bore: 71.5 mm x Stroke: 68.6 mm) is different than the "under-square" XS 750 engine which had a larger stroke than bore. The camshaft drive chain moved to the center of the engine. The XS1100 engine does not transmit power directly from the crankshaft to the clutch basket/input shaft, but rather via a wide hy-vo chain onto an intermediate jack-shaft with a cush-drive damper.
The engine rotation was therefore clockwise when viewed from the left side and not counterclockwise as all other inline four-cylinder motorcycle engines of the day. This jackshaft included a "cush-drive" shock damper needed for drive shaft drive trains. The starter also engaged the jackshaft to start the engine. The engine is mounted in rubber bushings making it an almost completely vibration-free running powerplant.
A significant advancement of the XS 1100 engine are the combustion chambers.
To make adequate power most modern motorcycle engines of the day including the XS 750 had simple hemispherical combustion chambers with domed pistons. This design has a major drawback in relatively long flame travel during combustion and therefore requires much spark advance, which in turn can cause severe preignition in high-performance engines. To improve combustion efficiency while virtually eliminating the possibility of preignition, Yamaha designed multi-angle "polyspheric" combustion chambers that required six different machining processes during manufacturing. This new design allowed for high compression without a large piston domes and large ignition advance. The XS 1100 valves were the same as previously used in the XS 750 engine, but their angle differed from the previous 3-cylinder engine. Carburetion was delivered by four Mikuni BS34 II constant velocity (CV) carburetors and ignition via a contactless, transistorized electronic ignition unit (TCI) with vacuum advance.
When the XS Eleven was introduced, it earned a reputation as a heavy, powerful and reliable bike. It was the fastest-ever production bike in 1978, for the first time posting a sub-12 second 1/4 mile time (11.78 sec. @ 114.21 mph with a top speed of 135 mph - Cycle World 2/78). In 1978 and 1979 it won Cycle World's Ten Best Bikes as the best Touring bike.
"Nobody gets far riding the XS Eleven before they become acquainted with the fact that it's strong; we had ridden ours over hundreds of open-road miles before going to the drag strip and knew it was a bullet." Cycle Magazine had this to say of the Eleven: "...the XS is a Rolls Royce with a blown Chrysler Hemi motor..."
The handling of the XS Eleven was not as well received. "When this behemoth of a motorcycle actually hits a corner at anything approaching interesting speeds then it takes a good deal of muscle to lay it down. While the Yamaha doesn't disgrace itself in corners (not as much as some Z1000s I have known, for example) it doesn't commend itself either." Testers of the day all echoed the same story: "The XS1100 was a solid bullet in a straight line, but cornering at high speeds was done at your own risk." "Cycle warned its readers that the bike could easily go, stop and steer — just never two at the same time." 'Which Bike' magazine simply described the XS1100 as having 'a bullet proof motor, and tea trolley handling'.
North American models
The XS Eleven made its debut in September 1977 (MY 1978) as the largest displacement motorcycle in production at that time. It featured a four-cylinder dual overhead cam engine, dual front disc brakes, a rear disc brake, shaft drive and cast aluminum wheels. The XS Eleven was the most powerful mass-production motorcycle of the late 70s and posted superior performance numbers compared to its competition.