| Specification | Value |
|---|---|
| Production Years | 1978 – 1985 |
| Engine Oil | SAE 20W-50 Mineral (2.25 L) |
| Tire Size (F/R) | F: 3.25 S 18 / R: 4.00 S 18 |
| Tire Pressure (F/R) | 1.9 bar / 2.1 bar |
| Battery Type | 51612 |
| Spark Plug | Bosch W 7 DC |
A unique engineering highlight of the BMW R 45 is its status as a member of the Typ 248 series. Unlike the larger “Slash” series boxers, the R 45 was designed with a shorter stroke and a more compact crankcase to specifically target the German 27-horsepower insurance class. This made it a high-quality, entry-level gateway into the world of BMW Motorrad, offering the same build quality as its larger siblings but in a more nimble, urban-friendly package.
Technical Engine Analysis
The heart of the R 45 is a 473cc flat-twin air-cooled boxer engine. To maintain the longevity of the valve gear and pushrod seals, MotoSpecsLab recommends strictly adhering to the SAE 20W-50 Mineral oil requirement. Modern synthetic oils of lower viscosity can lead to seepage in these vintage seals. The system requires exactly 2.25 liters for a standard change including the filter.
Chassis & Handling Dynamics
Equipped with 18-inch wheels both front and rear, the R 45 offers a distinct handling profile compared to the 19-inch front wheels found on the R 80 or R 100. For optimal stability and cornering precision, tire pressures must be maintained at 1.9 bar (27.5 psi) for the 3.25 S 18 front and 2.1 bar (30.5 psi) for the 4.00 S 18 rear. Under-inflation on the rear tire is a common cause of high-speed weaving in the Typ 248 frame.
Electrical & Ignition Maintenance
The electrical system is centered around the 51612 battery. Owners should ensure the ground strap to the gearbox is clean and corrosion-free, as this is a frequent point of failure for the Bosch starter motor. For the ignition system, the Bosch W 7 DC spark plug remains the gold standard for achieving a complete burn and preventing carbon buildup on the piston crowns during low-speed city commuting.
Maintenance FAQ
How often should I change the oil?
Given the air-cooled nature of the 0351 model, oil should be changed every 5,000 km (3,000 miles) or annually to prevent thermal breakdown.
Can I use a different spark plug?
While cross-references exist, the Bosch W 7 DC is specifically heat-rated for the R 45’s combustion chamber temperatures. Deviating may cause pre-ignition or fouling.