BMW Isetta 300

4-wheel

BMW made the Isetta its own.

They   redesigned   the   powerplant   around   a   BMW   one-cylinder,   four-stroke,   247   cc   motorcycle engine   which   generated   10   kW   (13   hp).   Although   the   major   elements   of   the   Italian   design remained   intact,   BMW   re-engineered   much   of   the   car,   so   much   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,   three   years   after   launching   the   conventionally   modern-looking   BMW   700,   BMW ceased production of Isettas. A total of 161,728 units had been built.

BMW Isetta 250

While   it   retained   the   "Bubble   Window"   styling,   it   differed   from   the   Italian   model   in   that   its headlamps   were   fixed   separately   to   the   sides   of   the   bodywork   and   it   carried   the   BMW   badge below   the   windscreen.   The   car   was   also   redesigned   to   take   a   modified   version   of   the   250   cc four-stroke   engine   from   the   BMW   R25/3   motorcycle   and   the   front   suspension   was   changed.   The single-cylinder   generated   9   kW   (12   hp)   at   5800   rpm.   The   crankcase   and   cylinder   were   made   of cast   iron,   the   cylinder   head   of   aluminium.   However,   the   head   was   rotated   by   180°   compared with   the   motorcycle   engine.   The   twin-bearing   crankshaft   was   also   different   in   the   Isetta   power unit,   being   larger   and   featuring   reinforced   bearings.   One   of   the   reasons   for   this   was   the   heavy Dynastart   unit   which   combined   the   dynamo   and   self-starter.   The   fuel   mixture   was   provided   by   a Bing   sliding   throttle   side   draft   motorcycle   carburetor.   In   addition   to   further   changes   of   detail, the   BMW   engineers   enlarged   the   sump   for   installation   in   the   car   and   cooled   the   engine   by   means of a radial fan and shrouded ducting. The   power   train   from   the   four-speed   gearbox   to   the   two   rear   wheels   was   also   unusual:   fixed   to the   gearbox   output   drive   was   something   called   a   Hardy   disc,   which   was   a   cardan   joint   made   of rubber.   On   the   other   side   of   it   was   a   cardan   shaft,   and   finally   a   second   Hardy   disc,   which   in   turn was   located   at   the   entrance   to   a   chain   case. A   duplex   chain   running   in   an   oil   bath   led   finally   to   a rigid   shaft,   at   each   end   of   which   were   the   two   rear   wheels.   Thanks   to   this   elaborate   power transfer,   the   engine-gearbox   unit   was   both   free   of   tension   and   well   soundproofed   in   its   linkage to the rear axle. In   Germany,   the   Isetta   could   even   be   driven   with   a   motorcycle   license.   The   top   speed   of   the Isetta 250 was rated as 85 km/h (53 mph). The   first   BMW   Isetta   rolled   off   the   line   in April   1955,   and   in   the   next   eight   months   some   10,000 of the "bubblecars" were produced.

BMW Isetta 300

In   1956,   the   government   of   the   Federal   Republic   of   Germany   changed   the   regulations   for   motor vehicles.   Class   IV   licences   issued   from   that   time   onward   could   only   be   used   to   operate   small motorcycles   and   could   no   longer   be   used   to   operate   motor   vehicles   with   a   capacity   of   less   than 250   cc.   At   the   same   time,   the   maximum   capacity   allowed   for   the   Isetta's   tax   category   was   300 cc.   Class   IV   licences   issued   before   the   change   in   the   regulations   were   grandfathered   and   allowed to be used as before. This   change   in   regulations   encouraged   BMW   to   revise   their   Isetta   microcars.   In   October   1956, the   Isetta   Moto   Coupe   DeLuxe   (sliding-window   Isetta)   was   introduced. The   bubble   windows   were replaced   by   longer,   sliding   side   windows.   The   engineers   had   enlarged   the   single   cylinder   to   a   72 mm   (2.8   in)   bore   and   73   mm   (2.9   in)   stroke,   which   gave   a   displacement   of   exactly   298   cc;   at   the same   time,   they   raised   the   compression   ratio   from   6.8   to   7.0:1.   As   a   result,   the   engine   power output   rose   to   10   kW   (13   hp)   at   5200   rpm,   and   the   torque   rose   to   18.4   N·m   (13.6   ft·lbf)   at   4600 rpm.   The   maximum   speed   remained   at   85   km/h   (53   mph),   yet   there   was   a   marked   increase   in flexibility, chiefly noticeable on gradients.

1956

Engine 295 cc 2 cylinders Power 13 HP Top speed 85 km/h Lenght/width 2,29 m/1,38 m Weight 340 kg