Vintage BMW Motorcycle Owners

Hi!

Can anyone tell me the exact difference between a R11 series 5 engine and an R12 engine?

Best regards, Frode

My understanding is the only difference is the serial number.

I think the cam followers and engine breather have minor differences.

The BMW Profiles book indicates that the R11-5 has an engine with a designation of M 56 S 5 while the R12 1-carb has a designation of M 56 S 6 (or 212...that might be associated with the frame). Not sure what that might translate to as internal differences.

The pictures in the respective parts manuals look identical to me, even the cam gear cover with its breather arrangement looks the same, and the "breather ring" that is on the front of the cam has the same part number for both models. However, the R11/5 and R12 crankcases have different part numbers, M56A150 and M56A160, respectively. And although the the cam follower bushings have the same part number, the followers themselves have different numbers. Unfortunately, they are not pictured in either parts book, so I have no idea what's different.

(The 212 numbers reflect the renumbering of all parts that the German Wehrmacht required in order to make things easier on their quartermasters. The leading 2 indicates that it's a part for a motorcycle, and I believe that the 12 indicates BMW.)

My understanding of the S5 breather…. it breaths through the tube in the casting all the way down into the filter cover under the engine. The “bung” in the engine front facilitates this. The “bung” in the R12 allows a banjo type breather fitting at this point.

The S5 cam follower bushings allow the follower to directly fit into them like the earlier R62/52 (different length). I thought R12 had a guide fitted where this bush fits and a smaller diameter cam follower runs in this guide. If you remove the R12 barrels can the cam follower slide out like the early models?