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.
Cycle World tested a BMW R27 in May 1964, noting its reputation for quality, reliability and longevity. The magazine said the engine unit’s rubber mounting made the R27 “the smoothest of all the 250s we’ve tested” when the revs were up. However, all those shafts and gears spinning at close to engine speed meant shifting required patience, especially in light of the engine’s considerable flywheel effect. That said, Cycle World‘s tester never found a false neutral, and the “real” neutral was easy to find at a standstill.
Cycle World also praised the R27’s finish, component quality and potential durability. It handled well at moderate speeds, but was inclined to wallow in the corners if pushed. Also raising an eyebrow was the “anti-dive” effect created by the Earles fork, which actually imparts a feeling of the front end lifting up on hard braking. Braking from the big alloy single-leading-shoe drums was excellent. But where the thumper really scored was in long-distance comfort. The testers noted that “the R27 will take a beating without complaint, although it is not really intended for that,” suggesting that the best way to ride the baby Beemer was to relax, slow down and enjoy the scenery.
There were, however, a few niggles. Starting from cold required just the right balance of “tickling” the carburetor and a whiff of throttle, and while the side-mounted kickstart worked fine when standing beside the bike, it proved impossible to operate from the seat. Stalling in traffic wasn’t recommended.
By the 1960s, the BMW R27 was really an anachronism, a small-capacity heavyweight motorcycle kitted out for sidecar work; underpowered, overweight and conservatively styled — understated to the point of being … well, boring. And premium-priced, too. In an age of desert sleds, bobbers and café racers, the R27 looked just plain dated and dull by 1966, the year it slipped into oblivion. But its solidity, durability and bulletproof construction, together with simple maintenance and a low-stressed drivetrain, make it a highly underrated and underappreciated classic. As current owners will tell you, they’re great bikes. Grab one while you can!
Contenders: 250cc rivals to the BMW R27
BSA C15 Star
Claimed power: 15hp @ 7,000rpm
Top speed: 70mph
Engine: 247cc air-cooled OHV single
Weight: 280lb (dry)
Price then/now: $745 (1967)/$1,400-$4,000
If the BMW R27 was a downsized R69S, then the C15 can be considered a grown-up Triumph Tiger Cub. Introduced in 1958 as a replacement for the aging C12 (the engine of which dated from before World War II), the BSA C15 Star was developed from Edward Turner’s 200cc Cub. The BSA’s cylinder was vertical rather than sloping, but retained the Cub’s external pushrod tube. The 67mm x 70mm crank used a plain bearing big end and ran on a drive-side ball race and timing side bushing.
The rest of the bike was quite conventional, with a unit-construction 4-speed transmission, duplex swingarm frame, and telescopic forks. C15T Trials and C15S Scrambles models followed, together with a SS80 (later Clubman) street model. These used a roller bearing big end to handle the extra power — and it was the pursuit of more power to compete with Japanese imports that proved the little Beezer’s undoing. The C25 Barracuda, produced from 1967-1970, used Victor-style ball and roller main bearings, but had a plain bearing big end that couldn’t cope with its claimed 25 horsepower at 8,000rpm. This was remedied in 1970 with an improved lubrication system, but the fix was too late to save its reputation.
A complete redesign for 1971 saw the humble C15’s final iterations, the B25T trail bike and the B25SS “Gold Star.” Unfortunately, while the bikes were much more reliable, by that time it was game over for BSA. The most durable BSA unit 250s to find are the roller big end C15 built from 1965-1967 and the later, low-compression Fleetstar.
Claimed power: 22hp @ 7,200rpm
Top speed: 80mph
Engine: 249cc air-cooled OHC single
Weight: 275lb (dry)
Price then/now: $579 (1963)/$2,000-$4,000
Ducati’s 250cc touring Monza and sporty Diana were responsible for building Ducati’s name in the U.S. market between 1961 and 1968. Though following the overall design and 74mm x 57.8mm bore and stroke dimensions of the F3 production racer, the street 250s shared almost no parts with their racing kin. Their engines were bevel-drive SOHC designs, but with spring-return valves. (Desmodromic operation would have to wait until the “wide case” engines of 1968-on.)
Ducati claimed 22 horsepower for the Monza and 24 horsepower for the Diana, with top speeds of more than 80mph, though these figures were pretty optimistic. Even “faster” was the Mark 3 Super Sport introduced for the U.S. in 1963, with a claimed 30 horsepower (sharing its engine with the 1962-on 250 Scrambler), and equipped with clip-ons, racing tires and a competition plate.
After 1964 all models got a 5-speed gearbox. The 250 Ducati Monza continued, joined by the 250GT (a Monza with the 17-liter Diana gas tank), while the 250 Mk3 replaced the Diana. Rare in the U.S. was the 250 Mach 1, essentially a Mark 3 but with sportier equipment and 28 horsepower.
Ducati “narrow case” singles are mechanically sound, but suffer the usual period Italian woes of suspect electrics and sometimes less-than-perfect paint and chrome. And while the later “wide case” desmo singles fetch more money, the earlier spring-valve 250s are lighter, more nimble and easier to maintain. MC
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