BMW K75

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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 sporty bike - accelerating from 0-60mph in 4.6 seconds for a top speed of 124 mph.

[edit] Engine and Transmission

All K75 models share the same drivetrain. 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.

[edit] Model Designations

Available unfaired as the K75, bezeled headlight with touring bags, 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 Tourer 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: Probably the best part of this bike is the engine. Liquid cooled, inline, fuel injected three cylinder on its side. Mine has 53K miles on it. One, "Old Smokey" on the internet has 340,000 miles on it! The fuel injection has never had an issue either. However, the cost and number of design flaws retire this bike long before the engine ever goes. It is also much different to work on than many Japanese motorcycles.

COST(new) K75S: $12,000 USD w/ABS in 1992.

BMW motorcycles’s are often ridden more miles than other brands. I have personally seen at least four K75's with close to one hundred thousand miles. My K75S has 54,000 miles on it. For an excellent tech resource which talks about some of these issues and how to fix them see [1]

Design Flaws There are at least twelve significant design flaws:

SPEEDOMETER: Multiple and well-known serious and expensive problems exist.

1) The speedometer was designed for use in airplanes by MotoMeter. In places like the southwest the plastic warps and the needles drag or stop altogether. Moisture gets trapped and cause the lens to fog and corrodes the wiring inside. 2) The wire contacts need to be greased and sometimes re-soldered on the main processor board. 3) The trip meter breaks so the miles can not be reset after filling the tank with gas. The trip meter is essential to knowing how many miles are left before the gas runs out. The bike averages forty-two miles per gallon (mpg). The Tank holds around 4.6 gallons and does not have a reserve. One fix is to install a bicycle speedometer, like the Sigma BC906 which has a top speed of around 160 miles per hour (mph). 4) Rebuilding the speedometer is available from a 3rd party at a cost of around $500. At the dealership a new unit runs about $1500. BMW improved the design with Gore-Tex vents, but it doesn't help much.

CLUTCH SPRINGS: Around 30,000 miles the clutch begins to slip due to insuficient spring pressure. This repair costs about one thousand dollars because of the time it takes to replace the dry clutch.

GAS TANK: Rubber cushions wear-out over time and if they are not replaced the gas tank cracks. Replacement cost is quite high at $700 for an unpainted tank or $1400 for a painted tank. This price does not include labor and all the parts gaskets pump et cetera that must be transferred to the new tank. Fortunately, the tank can be welded. Poorly designed vent to crankcase tube location under the tank requires exact positioning to avoid kinking which causes the tank to swell and crack. Epoxy should never be used on aluminum because the tank expansion will crack the glue in a few weeks.

RADIATOR FAN: The fan is used in cars and lacks sufficientlubrication causing it to seize if the bike sits unused for prolonged periods of time. The repair takes three hours and the fan costs $100.

WATER/OIL PUMP SEAL: Many pumps began to leak between 20 to 40K. Oil drips out the bottom weep hole. The impeller shaft rusts and requires replacement. The cost is about $500. BMW has updated the seal with an improved design.

CENTER STAND: The center stand fails from over use. The 1990 and newer models have added a piece of metal to reinforce the stand.

TRANSMISSION: If the bike falls on its left side and hits the gear shifter lever, excessive movement or "play" can develop. False neutrals are another well known problem when shifting gears similar to the late 80’s Harley Davidson but much worse.

SHAFT DRIVE: Some fail every 20,000 miles. Greasing both clutch side and rear spline is required every 20K miles which costs about $370 at the dealer.

HEAD LIGHT HI/LOW SWITCH: The switch becomes clogged with dirt and fail. Mine failed at about 45K. The switch cost about $70 and takes about one hour to replace.

VALVE OR ENGINE SEALS: If the bike is left on the side stand for a day or more oil leaks into the combustion chamber and a lot of blue smoke is emitted from the muffler when the engine is started. Always using the center stand when parking keeps the bike upright but also caused the center stand to fail, eventually, from overuse.

CRANKCASE BREATHER HOSE PCV: The tube is not thick enough and cracks at the clamps every year or 5,000 miles. Crankcase oil vapors leak down the left side of the engine. This can be repaired by cleaning the tube and applying liquid silcone and using larter automotive screw type clamps.

WARNING LIGHT: You get a red light that blinks then stays on. My computer indicates a loose wire. This is different from the ABS light blinking. Flickering of the warning light can be caused by a failing bulb in the tail section, either the brake light bulb or the running light bulb.

Age related Repairs: Seals dry up and unfortunately the cost of the repair exceeds the value of this motorcycle leading many owners to sell or retire their bikes as parts bikes. The timing cover seal is leaking oil. Front fork seals will cost $1300 because the tubes are rusted. The chrome tubes cost $640 for two tubes plus seals and labor at $75 per hour. The dealer recommended I contact a companay called Forks by Frank that makes fork tubes. I contacted the company and they do make tubes but need to know which of two possible brands and outer dimensions I have. My 1992 K75S has Showa forks as opposed to Fichtel and Sachs brand forks. The outer fork diameter is either 1.612 inches or 1.627. This information is not in any service manual and must be obtained by measuring with a vernier caliper tool.

My 1992 BMW K75S (manufactured on 11/91) has an upper outter fork tube diameter of 1.612" (40.95mm). Converting to metric is inaccurate according to Forks by Frank because the part is specified in inches. When I determine whether my forks were manufactured by Showa or Fichtel and Sachs I will update this page and try to provide pictures.

Despite all these issues I have grown to love this bike for its exceptionally vibration free motor and because it works nicely as every day transportation.