| Specification | Data |
|---|---|
| Production Years | 1938 – 1940 |
| Engine Type | Single-cylinder, 4-stroke OHV |
| Oil Grade | SAE 40 (Summer) / SAE 20 (Winter) |
| Oil Capacity | 0.8 Liters |
| Tire Size | F: 3.00 x 19 / R: 3.00 x 19 |
| Tire Pressure | F: 1.2 bar / R: 1.5 bar |
| Battery | B39-6 (6V 7Ah) |
| Spark Plug | Bosch W 175 T1 |
Historical Engineering Highlight: The BMW R 23 represents a pivotal moment in German motorcycling history. It was engineered specifically to address a 1938 legislative change that eliminated the tax-free status for 200cc motorcycles while simultaneously allowing riders to operate machines up to 250cc with the same license class. BMW responded by increasing the bore of the existing R 20 engine, creating a 10hp workhorse that became the standard for civilian and military dispatch reliability.
Technical Engineering Overview
The BMW R 23 (internal designation 0223/1) is a masterclass in pre-war minimalism and efficiency. Its longitudinal single-cylinder engine features overhead valves (OHV) and a shaft-drive system—a rarity for small-displacement bikes of that era. The frame is constructed from bolted pressed-steel sections, providing a rigid chassis that contributed to its legendary durability.
Maintenance Guide
1. Lubrication System
The R 23 utilizes a simple splash lubrication system. For modern preservation, it is critical to use non-detergent oils if the engine has not been retrofitted with modern filtration.
- Summer Usage: SAE 40 monograde.
- Winter Usage: SAE 20 monograde.
- Total Capacity: 0.8 Liters.
2. Electrical and Ignition
The electrical system is a 6-volt setup powered by a B39-6 (7Ah) battery. For optimal combustion and heat range management, the Bosch W 175 T1 spark plug (or modern equivalent) should be gapped according to period factory specifications. Ensuring clean contact points within the magneto is essential for consistent cold starts.
3. Wheels and Tires
Equipped with 19-inch wheels front and rear, the R 23 requires specific pressures to maintain handling characteristics on both paved and unpaved surfaces.
- Front (3.00 x 19): 1.2 bar (17.4 psi)
- Rear (3.00 x 19): 1.5 bar (21.8 psi)
Editor’s Verdict
At MotoSpecsLab, we rate the BMW R 23 as one of the most significant entry-level classics in existence. Its mechanical transparency makes it an ideal candidate for collectors who enjoy performing their own maintenance. While it lacks the raw power of the larger R-series boxers, its 250cc heart offers a pure, tactile connection to 1930s engineering.