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The BMW K100 is a 1000 cc touring motorcycle that was manufactured by BMW from 1983 to 1992. It was the bike that took (away) the public's perception of BMW as just a manufacturer of flat-twin boxer engines.
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Background
As the 1970's came to an end, BMW faced three problems from developing its flat-twin boxer engine further:
- Developing European Union emissions regulations, meant that more control was need over the amount of fuel entering the combustion chamber. From an engineering view point, this was easier to achieve with more cylinders of lower capacity
- The market-led development of bikes was leading to the Japanese factories developing smoother and quicker machines based around a 4cyclinder format
- Bike comparison in the media at the time was based around top speed, and a 4cyclinder when fully developed created more power, and should go quicker
In combination, this meant that BMW's marketing to users of a superior bike, allowing them to price at a premium, was being quickly lost, resulting in a loss of sales and market share.
Engine
The need for a quick development time scale of a clean burning 4cylinder engine, and the fact that Honda had developed a flat-4 boxer for the Honda GL1000 Gold Wing,[1] guided the design team led by Josef Fritzenwenger and Stefan Pachernegg to an existing liquid cooled Peugeot car engine.
To speed development but improve the engine, the team made two key developments. Firstly, as a car engine it was relatively large (most specifically wide, but also tall) compared to a motorcycle engine. As BMW needed something different to every other manufacturer, the choice was made to lay the engine flat in the frame, to keep the weight low and hence easily manageable. This is known as a longitudinal four because the crankshaft is in line with the direction of travel of the motorcycle. This configuration, although technically not new for motorcycles, had not been seen for many years, and over came the problem of splitting the crankshaft of the engine, and hence speeded development.
The second development took place around engine management, with Bosch Motronic fuel injection replacing carbureters, increasing power, power band and reducing fuel consumption.
These engineering choices made, meant that from start of the project to a marketable product, the K100 was on the market and being sold within four years.
The same team would later develop a three cylinder version of the engine for the 750cc BMW K75, and an improved four valve per cylinder head for the aerodynamic BMW K1.
K100
The original engine has its four cylinders arranged so that the crankshaft is on the right-hand side of the motorcycle, with the cylinders, pistons, camshafts, injectors and spark plugs on the left-hand side. This arrangement keeps the centre of gravity relatively low, which benefits handling; and the space behind the front wheel available for the radiator, resulting in a reduced width.
In addition, since the crankshaft is now on the right-hand side, access to the engine becomes much easier than in a conventional design, where the crankshaft is at the bottom (hence the term "bottom end"). BMW preferred a shaft-drive for smoothness, so a standard swing arm provided right side drive directly to the gearbox and onwards to the rear wheel. The 4-into-1 all stainless steel exhaust exited on the left hand side.
Brakes were twin-pot Brembo onto undrilled discs. Two different forks manufactures were used: Showa with an outer upper tube diameter of 1.612 in (40.9 mm) and Fichtel and Sachs measuring 1.627 in (41.3 mm). In later models, the standard swingarm was replaced with a Paralever single-sided swingarm, just as on the K1.
Model designations
Various models of the K100 were produced.
- K100, with no fairing
- KK100T, US only model with a windscreen, touring bags, engine crash bars, and rear top case
- K100C, with a small handlebar mounted 'cockpit' fairing
- K100S, with sports fixed fairing and lower bars
- K100RT, with full fairing for 'road touring'
S and RT versions have a rear disc brake and 17 inch rear wheels whereas the others have a single leading shoe drum brake and 18 inch rear wheels. A stiffer, "anti-dive" front suspension was added to the S and RT model. Later RT version has a windshield that can be raised or lowered, as some taller riders complained of wind buffeting with the smaller S model stock windscreen.
The K-series offered additional refinements including: all stainless steel exhaust, rust-free aluminium fuel tank, anti-lock brakes or ABS, adjustable headlight, high capacity 460 watt alternator, cigarette lighter accessory plug-in, self cancelling signal lights.
Sales
Although sales were initially modest, buyers eventually warmed to the multi-cylinder BMW, and the 3-cylinder derivation in the form of the BMW K75. The K100 was a relative sales success, stemming the losses to the Japanese and changing the media and public perception of BMW.
The four-cylinder engine suffered from secondary vibration, but in three-cylinder format of the K75 was far smoother. The engineers had anticipated this, and had designed in excellent vibration isolation, but it was the only technical glitch.
The competition were never far behind in performance on launch, updates were modest, while engine performance was stepped up with the September 1988 launch of the radically aerodynamic BMW K1.
References
External links
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Wikimedia Commons has media related to: BMW K100 |
- K bikes at the Open Directory Project
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