| Attribute | Specification |
|---|---|
| Production Years | 1978 – 1985 |
| Engine Type | Air-cooled, 2-cylinder Boxer |
| Oil Capacity/Type | 2.25 L / SAE 20W-50 Mineral |
| Front Tire | 3.25 S 18 |
| Rear Tire | 4.00 S 18 |
| Spark Plugs | Bosch W 5 D / NGK BP7ES |
| Battery | DIN 520 15 |
Historical Context: Unlike its larger R-series siblings, the BMW R 45 (Internal Code 0354) was specifically engineered with a unique short-stroke engine architecture. This wasn’t just a sleeved-down R 65; the R 45 was designed to meet the German 27hp (20kW) insurance class, making it one of the most accessible yet over-engineered entry-level motorcycles in BMW’s history.
Engineering Overview
The R 45 utilizes the Type 248 engine, a more compact version of the traditional BMW Airhead. By reducing the stroke to 44mm, BMW created a high-revving boxer (for the era) that maintained the smoothness the brand was known for. While it lacked the raw torque of the R 100, its agility and lower center of gravity made it a favorite for European urban commuting and light touring.
Maintenance Essentials
Lubrication System
The R 45 relies on a traditional mineral-based lubrication system. For the 0354 model, SAE 20W-50 Mineral oil is the gold standard. Modern synthetic oils are often too thin for the tolerances of the 1970s oil pumps and seals. Ensure you have 2.25 liters available for a full filter-change service.
Tires and Handling
The R 45 is sensitive to tire pressure due to its relatively narrow 18-inch wheels. Maintaining the correct PSI is critical for preventing “head shake” at higher speeds:
- Front (3.25 S 18): 1.9 bar (27.5 psi) solo / 2.1 bar (30.5 psi) loaded.
- Rear (4.00 S 18): 2.1 bar (30.5 psi) solo / 2.5 bar (36.0 psi) loaded.
Electrical and Ignition
The 0354 series uses the DIN 520 15 battery. Given the modest output of the Bosch alternator at low RPMs, ensuring clean terminals is vital for cold starts. For ignition, we recommend NGK BP7ES or Bosch W 5 D plugs, gapped to factory specifications to ensure efficient combustion in the high-compression chambers.
MotoSpecsLab Verdict
The BMW R 45 is a masterclass in durable, entry-level engineering. While it won’t win drag races, its mechanical longevity is legendary. For the modern collector, it represents an affordable entry into the world of Airheads, provided that the mineral oil and valve clearances are maintained with Teutonic discipline.