1951 BMW R51/3

BMW started to offer a 500cc motorcycle after the war beginning in 1950. They dusted off their design from 1938 for the engine, frame and suspension and the pre-war R51 was reborn as the R51/2. BMW redesigned the engine and in 1951 an all new engine was put into the same pre-war plunger frame and the R51/3 was born (see a trend?) An example of this new engine in an old frame is on sale now here on eBay.

From the seller

It  has  been  restored,  but  needed  some  parts  to  finish;  proper  controls,  tail light,  a  few  small  parts.  I  drove  it  around  the  back  roads  of  CT  over  the  summer,  putting  on  about  200  miles.  Odometer  now  shows  700,  clearly  not  original  miles.   The  bike  starts  easily  and  runs/ idles  as  it  should.  Clutch,  brakes ,  transmission  are  fine.  the  bike  is  a   pleasure  to  ride,  although  not the  fastest  thing  around ( maybe  it  was  in  1951…) The  restorer  installed  alternator/  electronic  ignition  unit,  which  is  12  volt.  This  makes  for  bright  lights  and  eliminates  the  magneto.
In  conjunction  with  the  alternator,  there  is  a  pull-push  switch  on  the  bottom  of  the  headlight (  which  is  otherwise  correct),  the  lights  are  controlled  by  the  key  switch.

From 1951 until 1954, the R51/3 was offered as a sport/single as a companion to the 600cc R67 that was often attached to a sidecar for the family. Performance came from a squared bore and stroke of 68cm and would produce 24hp at 5800rpm and gives you a top speed of 83mph. 18,420 were produced in the four years of production with some changes being made over those years.

The bike offered here on eBay has the half hubs and metal shrouds over the front telescoping fork springs, each original 1951 items. They were replaced with full width hubs and rubber gators by 1954. The mufflers for 1951 would have originally been either the stylized fishtail, or swallow tail muffler, the change to the cigar style in later years mandated by noice restrictions. These later mufflers can be considered original as many early bikes were retrofitted back in the 1950’s when the factory had to comply with bikes still unsold. The rear plunger suspension on this bike are also topped off with a mushroom shaped cap, were later frames had a large threaded nut capping what was considered suspension in the day.

If you were to look at the R51 or R51/2 sitting next to the R51/3, visually the only difference would be the engine. Prior to the new design, the generator sat on the top of the engine, under the gas tank, the R51/3 engine moved this under the front engine cover. The old design also gave each cylinder its own cam shaft to operate the push-rods, and the new /3 engine only has one cam to operate all four valves. The R51/3 even kept the hand shift lever on the transmission that was a hold over from pre-war bikes.

This is a very nice example of the post war BMW and is very collectable when compared to the R50/2 (confused?) that replace this model in 1955 and offered until 1969. If you are already a BMW owner this is likely high on your wish list, but if you are looking for your first BMW, this would not be a bad starting place.  BB