1957 BMW Isetta 300
edited by David Barth, 10 January 2009.
Courtesy The Forney Museum of Transportation at 4303 Brighton Blvd., Denver,
Colorado.
Information is from Wikipedia, the free encyclopedia.
Photos were taken in February 2009.
The Isetta was one of the most successful microcars. Although the design originated in Italy, it was built in a number of
different countries, including Spain, Belgium, France, Brazil, Germany, and Britain.
Because of its egg shape it became known as a bubble car, a name later given to other similar
vehicles. Other countries had nicknames. In Germany it was das rollende Ei ("rolling egg"), Sargwagen ("coffin car."
The name apparently came from the small (or rather nonexistent) distance between the passengers and oncoming traffic). It
was also known as the Knutschkugel ("snogging ball"). In France it was the yogurt pot. In Brazil it was the bola de
futebol de feneme (soccer ball of FNM [a truck]), and in Chile it is still called the "huevito" (little egg).
BMW made the Isetta its own. They redesigned the power plant around a BMW one-cylinder, four-stroke, 247 cc motorcycle
engine. Although the major elements of the Italian design remained intact, BMW re-engineered much of the car, so that
none of the parts between a BMW Isetta Moto Coupe and an Iso Isetta are interchangeable. The first BMW Isetta appeared
in April, 1955. In May 1962, two years after launching the BMW 700, BMW ceased production of Isettas. A total of 161,728
BMW Isettas were built. In Germany the Isetta could be driven with a motorcycle license.
In October 1956 the BMW Isetta 300, Isetta Moto Coupe DeLuxe, was introduced. The bubble windows were replaced by
longer, sliding side windows. The car continued to use the single-cylinder, 4-stroke engine from the BMW R25/3 motorcycle
which was enlarged to a 72 mm bore and 73 mm stroke, to give a displacement of exactly 298 cc. The compression ratio was
increased from 6.8 to 7.0:1. The engine generates 13 hp (10 kW) at 5200 rpm. The maximum speed is
85 km/h (53 mph).
The crankcase and cylinder are made of cast iron, and the cylinder head is aluminum. The car features a Dynastart unit
which combines the generator and self-starter. The fuel mixture is provided by a Bing sliding throttle side draft
motorcycle carburetor.
The power train from the four-speed gearbox to the two rear wheels is unusual. Fixed to the gearbox output drive
is something called a Hardy disc, which is a cardan joint, made of rubber. On the other side of it is a cardan shaft,
and finally a second Hardy disc, which in turn is located at the entrance to a chain case. A duplex chain running in an
oil bath leads to a rigid shaft, at each end of which are the two rear wheels. Thanks to this elaborate power
transfer, the engine-gearbox unit is both free of tension and well soundproofed in its linkage to the rear
axle.
Manufacturer: BMW
Name: BMW Isetta 300
Production: 1956 to 1962
Predecessor: BMW 250
Successor: BMW 600
Engine: single cylinder, 4-stroke, based on a BMW R25/3 motorcycle engine
Displacement: 298cc
Bore: 72mm
Stroke: 73mm
Compression Ratio: 7:1
Power: 13 brake horsepower (10 kw)
Top Speed: 53 mph (85 km/h)
Transmission: 4-speed, manual
