While the ‘Flying Brick’ moniker is often associated with the K 100, the BMW K 75/C (K569) holds a unique place in motorcycling history as the only mass-produced three-cylinder motorcycle engine BMW ever developed. To achieve unparalleled smoothness, BMW engineers utilized a counter-rotating balance shaft spinning at twice the crankshaft speed, making the K 75 famously smoother than its four-cylinder sibling.
| Quick Specifications: BMW K 75/C (1985-1990) | |
|---|---|
| Engine Type | Liquid-cooled, Inline-3, 4-stroke |
| Engine Oil | SAE 20W-50 API SF/SG/SH (3.5 L) |
| Spark Plugs | Bosch X5DC |
| Tire Size (Front) | 100/90 – 18 56V |
| Tire Size (Rear) | 120/90 – 18 65V |
| Battery Type | 51913 / 52515 |
Technical Overview
The K 75/C, produced between 1985 and 1990, was designed as a refined middleweight tourer. The K569 chassis provided a stable platform for the 740cc longitudinal engine. Unlike many contemporaries, the K 75 utilized Bosch LE-Jetronic fuel injection, a sophisticated system for the mid-80s that ensured reliable cold starts and consistent power delivery across the rev range.
Maintenance Guide
Lubrication System
For optimal protection of the internal components and the shared gearbox environment, MotoSpecsLab recommends SAE 20W-50 meeting API SF, SG, or SH standards. The total capacity is 3.5 Liters. Given the longitudinal layout, ensuring the oil filter is torqued correctly is vital to prevent leaks onto the dry clutch assembly.
Ignition & Electrical
The K 75/C relies on Bosch X5DC spark plugs. Maintaining the correct gap is essential for the electronic ignition system to function efficiently. For the electrical system, the bike typically utilizes a high-capacity battery, either the 51913 or the larger 52515 variant, to handle the demands of the fuel pump and cooling fan.
Chassis & Tires
Handling precision on the K569 depends heavily on tire condition and pressure. The factory specifications are 100/90 – 18 56V for the front and 120/90 – 18 65V for the rear. For standard solo riding, maintain 2.2 bar (31.9 psi) in the front and 2.5 bar (36.3 psi) in the rear.
The MotoSpecsLab Verdict
The BMW K 75/C remains a paragon of longevity. It is not uncommon to see these machines exceeding 200,000 kilometers with original internals. Its lack of vibration and linear power delivery make it a connoisseur’s choice among vintage BMW enthusiasts. Proper adherence to the 20W-50 oil regimen and cooling system maintenance are the keys to preserving this ‘Triple’ for decades to come.