Originally Posted by isdt BMW
/3 twins stopped in 1954, this bike is not a /2, it is a R-50. the /2 started when an extra gusset was added to the frame in front of the swingarm. there are a few subtle differences between the first series and the /2 series. the twin cam motor stopped with the 1950 R-51/2. The bike looks clean and is well worth 2500. set the front fork in the solo position before riding without a sidecar. GET THE SLINGERS DONE, they are your oil filter. Get the books and talk to vintage BMW guys. good luck, they are great bikes.
I thought that the / number related to the engine? I believe the R51/3 engine was basically the same until some redesigns made it the /2? For instance, I have been told at service school and other places that the R69S engine really wasn't a /2 anymore after getting it's rear main bearing redesigned in '63 I believe? I know it's just semantics and engine design but . . . . Maybe they said it never was for the different heads?