Forum bmwbike.com

Hi to all.

I have a strange problem of a bike with VIN plate and frame/engine serial numbers of a 1954 R51/3, but a frame/tank/Earls fork of a R50. The cylinder head and barrel have 9 cooling fins each, and the rocker cover 6 fins, if that helps anyone.

I need new carburettors so I wonder what will happen if I buy R50 carb's, and it eventually turns out to be essentially a R51/3 engine. Will they fit the manifold? Will I get decent performance? Any help is much appreciated

Hello Scott,R51/3 heads have 22mm intake ports and matching 22mm carbies,R50 heads have 24mm intakes and matching 24mm carbies, hope this helps. Can supply numbers of these if you need them, lets know. Regards Geoff.

It will still run just fine with R50 carbs, R51/3 Carbs will be expensive and tough to find.

Do you know whether it is an R50 engine or a R51/3 engine? If it is an R51/3 Engine the serial number will be stamped underneath the embossed BMW letters on a flat spot on the left side of the engine. If it is a R50, the serial number is stamped on the right side of the engine and there is no flat spot under the BMW letters (used for stamping) which is still on the left side of the engine.

If it is a R51/3 engine, someone probably put the engine in a R50 bike, swapped the name plate, and maybe re-serial numbered the frame....