| Component | Specification |
|---|---|
| Production Years | 1985-1995 |
| Engine Type | 740cc Inline-Triple, Liquid-Cooled |
| Engine Oil | SAE 20W-50 API SF, SG, or SH (3.5 L) |
| Tires (Front/Rear) | 100/90 V 18 / 130/90 V 17 |
| Spark Plug | Bosch X5DC (Gap: 0.6 mm) |
| Battery | 51913 (Std) / 61 21 1 459 516 (ABS) |
While most enthusiasts associate BMW’s ‘K-Series’ with the massive K100, the BMW K 75 S holds a unique place in engineering history: it is widely considered the smoothest engine BMW ever produced. By utilizing a counter-rotating balance shaft driven by the crankshaft, BMW engineers effectively eliminated the secondary vibrations inherent in the three-cylinder layout, resulting in a ‘sewing machine’ precision that often surpassed its four-cylinder siblings.
Technical Deep Dive: The Triple’s Triumph
The K 75 S (Sport) variant was the aerodynamic peak of the K75 range. It featured a frame-mounted bikini fairing, stiffer suspension, and a rear disc brake, distinguishing it from the standard ‘C’ or ‘RT’ models. The 740cc longitudinal engine produced approximately 75 horsepower, delivered through a dry clutch and shaft drive—a hallmark of BMW reliability.
Maintenance Specifications
Maintaining the K 75 S is straightforward for the home mechanic, provided you adhere to the specific fluid and electrical requirements of the Bosch LE-Jetronic fuel injection system.
Lubrication and Fluids
The K75 engine is a flat-tappet design that thrives on high-zinc oils. We recommend SAE 20W-50 API SF, SG, or SH grade oils. The total capacity is 3.5 Liters. Using modern ‘Energy Conserving’ oils can be detrimental to the internal components and the dry clutch if seals are compromised.
Tires and Pressure Management
Handling on the K 75 S is highly sensitive to tire pressure. For the standard 100/90 V 18 (Front) and 130/90 V 17 (Rear) setup, MotoSpecsLab recommends the following:
- Solo Riding: Front 2.2 bar (32 psi) / Rear 2.5 bar (36 psi)
- With Passenger/Luggage: Front 2.5 bar (36 psi) / Rear 2.9 bar (42 psi)
Electrical System
The ignition system relies on Bosch X5DC spark plugs. It is critical to maintain a gap of 0.6 mm to ensure consistent combustion. For battery replacements, the 51913 is the standard unit, though models equipped with the early ABS systems require the high-output 61 21 1 459 516 variant to prevent low-voltage fault codes during startup.
Editorial Review: The ‘Flying Brick’ Legacy
The K 75 S is an exceptional example of ‘over-engineering’ from an era when BMW aimed for 200,000-mile longevity. Its power delivery is linear, its cooling system is robust, and its ergonomics remain comfortable for long-distance touring. While it lacks the raw torque of modern triples, its refinement and historical significance make it a premier choice for collectors and daily commuters alike.
Frequently Asked Questions
What is the fuel capacity?
The K 75 S features an aluminum tank with a capacity of approximately 21 liters (5.5 US gallons), including a 5-liter reserve.
How often should I grease the drive shaft splines?
At MotoSpecsLab, we recommend cleaning and lubing the clutch and drive shaft splines every 20,000 miles (32,000 km) with a high-moly paste to prevent premature wear.