The 250cc BMW R27

Best bets on tomorrow’s classics: 250cc BMW R27

| July/August 2012

  • BMW R27
    The BMW R27’s solidity, durability and bulletproof construction, together with simple maintenance and a low-stressed drivetrain, make it a highly underrated and underappreciated classic.
  • Ducati Monza
    Ducati’s 250cc touring Monza and sporty Diana were responsible for building Ducati’s name in the U.S. market between 1961 and 1968.
  • BSA C15 Star
    If the BMW R27 was a downsized R69S, then the BSA C15 Star can be considered a grown-up Triumph Tiger Cub.

  • BMW R27
  • Ducati Monza
  • BSA C15 Star

250cc BMW R27
Claimed power: 18hp @ 7,400rpm
Top speed: 80mph
Engine: 247cc air-cooled OHV single
Weight: 356lb (wet)
Price then/now: $850/$5,000-$8,000

It’s the BMW you might never have seen, yet for a period it was one of the Bavarian maker’s most successful products. In fact, BMW built more than 150,000 of its 250cc singles between 1948 and 1960, including 100,000 of the 1950-1956 R25 model alone.

So it turns out the bike maker best known in North America for its boxer twins made scads of vertical singles, too. If you’re not familiar with the model, it’s because most were sold in Europe, where the market for two-wheeled daily transportation (rather than weekend berm-bashers) was much bigger. The 250 best known in the U.S. is, ironically, the last and least numerous of the range, the BMW R27, of which just 15,000 were made from 1960-1966.

The 1948 R24 was BMW’s only post-WWII bike with a hardtail frame, replaced in 1950 by the R25 with plunger rear suspension. Both bikes used a 68mm x 68mm pushrod 4-stroke single engine based on the pre-war R23 that produced 12 horsepower (13 horsepower for the 1953-56 R25/3). 1956 brought the R26, with an Earles front fork and rear swinging arm replacing the telescopic fork and plunger rear of the R25. Power increased to 15 horsepower. The R27 arrived in 1960 with 18 horsepower and a rubber-mounted powertrain. Apart from the engine, much of the rest of the R27 looked like its twin-pot sibling, the R69S — which isn’t  surprising, because it shared almost all its components, meaning the R27 was no lightweight.

A curiosity retained on the R27 was the Ernest Earles-designed leading-link front fork. The Earles design offered adjustable trail and also provided excellent lateral load resistance, both important for sidecar applications. However, the Earles front end was typically much heavier than a telescopic fork, so it also added unsprung weight.

Just like the boxer twins, the R27’s crank ran longitudinally, spinning an automobile-style flywheel and engine-speed diaphragm-spring clutch driving an idler shaft. The idler was needed for the sideways-operating kickstart, and transferred drive to the 4-speed transmission and shaft final drive.

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