| Specification | Data |
|---|---|
| Model Series | BMW R 26 – 224/5 |
| Production Years | 1955 – 1960 |
| Engine Type | 247cc Single-Cylinder OHV |
| Oil Requirement | SAE 30 (Summer) / SAE 20 (Winter) Non-Detergent (1.2 L) |
| Tire Size | F/R: 3.25 x 18 |
| Electrical System | 6V 7Ah (Type 3R2) |
| Spark Plug | Bosch W 240 T 1 (Modern: NGK B7HS) |
The BMW R 26 (internal designation 224/5) represents a watershed moment in post-war Bavarian engineering. While its predecessor, the R 25/3, relied on a telescopic fork and plunger rear suspension, the R 26 introduced the revolutionary Earles Fork (leading link) front suspension and a swing-arm rear. This “full swing-arm” chassis design provided unprecedented stability and comfort, effectively making it the most sophisticated 250cc motorcycle of its generation.
Engineering Excellence
At the heart of the R 26 is a 247cc vertical single-cylinder engine producing 15 horsepower at 6,400 RPM. This was a notable increase over the R 25/3, achieved through a larger Bing carburetor (26mm) and higher compression. The engine is longitudinally mounted, driving a four-speed gearbox via a dry single-plate clutch, eventually reaching the rear wheel through BMW’s signature enclosed driveshaft.
Maintenance Guide: Preserving the Legend
Lubrication System
The R 26 utilizes a splash and pressure lubrication system. Because these engines do not feature a modern oil filter (retaining only a wire mesh strainer), it is critical to use Non-Detergent oil. Detergent oils keep contaminants in suspension to be caught by a filter; in the R 26, contaminants must settle at the bottom of the sump. Use 1.2 liters of SAE 30 in summer and SAE 20 in winter.
Chassis and Tires
Maintaining correct tire pressure is vital for the unique handling characteristics of the Earles Fork. For solo operation, the front should be set at 1.2 bar (17.4 psi) and the rear at 1.5 bar (21.7 psi). If carrying a pillion passenger, increase the rear pressure to 1.9 bar (27.5 psi) to prevent wallowing in corners.
Electrical and Ignition
The 6V electrical system is powered by a Noris generator. The battery (6V 7Ah Type 3R2) requires regular electrolyte level checks. For ignition, the original Bosch W 240 T 1 is now commonly replaced with the NGK B7HS or Bosch W4AC. Ensure the spark plug gap is maintained at 0.6mm (0.024 in) for optimal combustion.
MotoSpecsLab Verdict
The BMW R 26 is more than a vintage motorcycle; it is a masterpiece of mid-century mechanical durability. For the modern collector, it offers a tractor-like reliability paired with the sophisticated ride quality of the full swing-arm frame. Adhering to the non-detergent oil requirements and precise tire pressures will ensure this machine remains roadworthy for another half-century.
Frequently Asked Questions
Q: Can I use modern multi-grade synthetic oil?
A: No. It is highly recommended to stick to single-grade non-detergent oils. Modern detergents can loosen decades of sludge, potentially blocking internal oil galleries.
Q: What is the maximum speed of the R 26?
A: The R 26 has a factory-rated top speed of approximately 128 km/h (80 mph), though a comfortable cruising speed is closer to 90-100 km/h.