BMW K75

File:K75.jpg

1993 BMW K75

1993 K75S with Belly Pan and touring bags

Produced from 1985-1995, the BMW K75 was a successful entry-level sport touring motorcycle. When it was introduced, the K75 was BMW's cheapest motorcycle. It was a supposed to be a sport bike offering a claimed acceleration of 0-60mph in 4.6 seconds and a top speed of 120 mph.

Engine and Transmission

All K75 models share the same drive train. They are powered by a 740cc in-line three-cylinder, Bosch fuel injected, engine. The US EPA specific engine produce 68 BHP while all others produce 75. It utilizes a five-speed transmission and a shaft-driven final drive. The engine used by the K75 is often described as "bulletproof," indicating that it is quite reliable. This engine has an advantage over the K100's larger four-cylinder because it has perfect primary balance via counter rotating shaft, opposed to the K100's unbalanced four cylinder engine which is noted for its vibration.

Model Designations

Available with no fairing as the K75, a windscreen with touring bags, engine crash bars and rear top case, only in the US as the K75T, with a small handlebar mounted 'cockpit' fairing K75C, Sports fixed fairing and lower bars on the K75S, and the full faired Touring K75RT. 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 model.

Engine

Possibly the greatest strength of the K75 lies in its engine, which is a liquid-cooled, inline, fuel injected three cylinder design rotated 90 degrees. It is not unusual for this engine to go more than 200,000 miles without significant repair. One example, "Old Smokey," has accumulated more than 340,000 miles. The engine is almost vibration-free, an accomplishment which few manufactures have achieved in the two decades following this design. The bike was also one of the first motorcycles to be equipped with a catalytic converter and stainless steel exhaust. The engine was designed to be less vulnerable to damage should the cycle fall over.

Background and Issues of the New Design

The K-bike lineup, including the K75 and K100, were not just new models; these designs were radical departures from almost every aspect of previous ones. The K-bikes introduced new technology and refinement for a premium brand. BMW and Harley-Davidson were the only major manufactures that did not offer liquid-cooled engines. Competing brands, notably of Japanese manufacture, were touting the superiority of their liquid-cooled engines and had introduced low maintenance shaft-drive technology into a growing number of their models.

Two unexpected surprises occurred: the industry was caught by surprise by an unprecedented multi-year decline in motorcycles sales, and BMW was faced with a rebellion of existing R-bike owners who threatened to abandon the brand altogether if the air-cooled boxer motor was eliminated. R-bike owners had become accustomed to easy maintenance and a tried-and-true design which had remained fundamentally unchanged for decades. The K models required less frequent maintenance intervals than the older R models but were much more time consuming and difficult to work on. The parts for the K bike are extremely expensive, often twice as much as R-bike parts. As a result, the K-bikes failed to replace the older air-cooled R-bikes or Boxers which were updated with oil-cooled cylinder heads. As a result, R-bikes make up about eighty-five percent of the motorcycles that BMW produces.

The K-bikes brought unprecedented refinements in the motorcycle world including: computer-controlled fuel injection, catalytic converter, all stainless steel exhaust, rust-free aluminum gas tank, anti-lock brakes or ABS, mono-shock absorber, rear wheel attached by a mono-arm, tool-less adjustable headlight, 460 watt alternator, cigarette lighter accessory plug-in, self-canceling signal lights. It would take more than two decades for other brands to catch-up. The new engine of the K75 produced some of the lowest vibration of any motorcycle ever made. It was superior to the K100 which was designed a few years earlier. These amenities came at a price: $10,000 for a loaded K75S in 1992.

Twenty years later the K-bikes have shown tremendous strengths and weaknesses. The engines offered outstanding reliability and low maintenance over hundreds of thousands of miles. Unfortunately, the rest of the bike suffers from an expensive and long list of problems resulting from a design that lacked real-world data. Owners especially those that bought the bike second hand were shocked by the repair bills. The design was criticized for its ugly brick-like appearance, the engine for being like a sewing machine. Finally, the skill-set required to work on or diagnose problems with the bike are different from any model past or present. Some people believe that BMW engineers overreacted by discontinuing the K75 because of its extensive legacy of problems. The wonderfully reliable, low maintenance, vibration-free three cylinder engine was discontinued in 1995 and has never returned.

Costly problems resulting from the new design.

Speedometer

The speedometer was designed for use in airplanes by MotoMeter. In the southwestern United States the plastic warps and the needles drag or stop altogether. Moisture gets trapped and cause the lens to fog and corrodes the wiring inside. The wire contacts need to be greased and sometimes re-soldered on the main processor board. The trip meter breaks so the miles can not be reset after filling the tank with gas. Rebuilding the speedometer is available at a cost of around $500. A new unit is $1500. BMW acknowledged the problem by adding a Gore-Tex vents to reduce fogging.

Clutch Springs

Somewhere between 20,000 to 30,000 miles the clutch springs fail to provide sufficient spring pressure. BMW acknowledged the problem by offering upgraded springs. The repair costs about $1000 due to the time to access the dry-clutch.

Gas Tank

Rubber cushions wear-out over time and if they are not replaced the gas tank cracks. Replacement cost is $700 for an unpainted tank or $1400 for a painted tank not including internal parts or labor. Epoxy cannot be use to repair the crack.

Radiator Fan

The electric fan motor has a problem with melting plastic brush holders. The symptoms mimic a simple lack of bearing lubrication. Motor replacement is required.

Water and Oil Pump Seals

Leaks between 20,000 to 40,000 miles. Oil drips from the weep hole on the bottom of the pump. The impeller shaft rusts and requires replacement. The repair is about $500 including labor. BMW acknowledged the problem with an improved seal.

Center-Stand

To avoid the oil-smoke problem when starting the engine owners constantly used the center-stand instead of the kick-stand. This unexpected heavy use caused the welds fail on the center-stand. The bike would fall on to the ground. BMW acknowledged the problem by recalling and replacing and later redesigning the center-stand on all models after 1990.

Transmission

False neutrals between gears when shifting are another well-known problem that has effected many older R-bikes. Excessive movement know as play or slop can develop as a result of a lose grub screw or set screw inside the transmisson.

Engine Smoke at Startup

Another familiar problem results from the bike being left on the kick-stand overnight. The design of the motor allows oil to leak into the combustion chamber. The result is a lot of blue oil-smoke after the engine starts. This is very ironic considering the fact that BMW had produced similar horizontal engines for decades. It is hard to believe that the engineers didn't catch this in the design phase. The problem was never resolved.

Rotors Crack Some units developed cracks in-between the vent holes in the front rotors and warping in the rear rotor. BMW changed the rear rotor to a thicker solid rotor and hardened the front rotors which required different calipers.

Drive Shaft Splines Problems Drive shafts could wear excessively and seize or bind. BMW had the shafts nickel-plated from approximately 1988 on.

Steering Head Lock Fails to lock.

Crankcase Breather Hose PCV Valve

The crankcase elbow-tube cracks at the clamps yearly. One resolution involves coating the tube with Liquid Electrical Tape or silicone sealant.

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Conclusion

In 2004, BMW introduced a third generation of the K-bike line. The new model makes a radical break from BMW tradition by utilizing an engine and transmission design that conforms more closely to industry standards. The dry clutch is replaced with a wet clutch, and the engine is rotated ninety degrees to the right. The result combines reliable time-tested features, established by Japanese manufactures, with BMW’s Duoleaver front suspension system and Paralever shaft-drive technology in the rear. The promise is the best of both worlds. In keeping with the second generation K-bike line, there has been no mention of replacing the Boxer engine. This may be an attempt to broaden the appeal of BMW motorcycles, while retaining the some of the unique features that attracted existing customers and differentiate BMW from other manufactures.

External links

• An outstanding explanation of the cause and history of BMW's past transmission problems
• Internet BMW Owners Group - Excellent Repair Resource
• Phil Hawksley's BMW Motorcycle Information Site
• Spline & Rotor Problems
• Original Purchase Price 1992 (in British Pounds?)