Forum bmwbike.com

Hello to all,

I bought a bike in Vietnam with frame plate 1954 R51/3. However the engine and frame serial no. is 540 776 which does not fit with a R51/3. It also has leading link front suspension and appears to be an r50/2.

I suppose it is possible the bike is a copy but it appears very genuine BMW to my mechanic.
Any suggestions on the serial number issue?
Scott Wilkinson, Australia

My tables from Mobil Tradition's Motorcycles from Munich 1923-1969 show engine and frame numbers for the R51/3 to be 522001-540950, so the numbers are OK.

I've never seen an earls fork fitted to a plunger frame, however, but I suppose it is possible. Does it have a plunger rear or a swingarm?

Best regards,

Bruce

Thanks Bruce,

I have just had word from BMW Germany to say this bike is a R51/3 delivered to Saigon in 1954 (according to the serial no.)
.
I cannot explain the fact that it has Earles forks, a rear swingarm and no manual gear shift at the back of the engine...Also it has 3 fins on the rocker cover, not 6 like an R51/5.
it looks like an R50 from pictures on the web.....

I must admit it is very confusing when I need to buy new carb's and don't know what model it is.

Are the numbers stamped into the frame and engine, or just on the builders plate?

Bruce,
the numbers are stamped on frame and engine, with the little round BMW logos either side. They look original to me but I am no expert.
Also the cylinder barrels have 9 fins, heads have 9 and rocker cover 3 fins. This is also apparently an R50 feature?
Cheers

Are the rims 19" or 18"... All R51/3's had 19" rims and then the R50 (which started in '55) had 18" rims. My guess is you have a really early R50. The valve covers sound like they are from a R69. I doubt someone converted a R51/3 frame to a swingarm and added the earls forks... but who knows..
Is the tank teardrop shaped, with a tool box lid on the top? (another R51/3 feature) and is the drive shaft exposed and chromed? (R51/3) or enclosed? (R50)

Thanks for the tips. The tank has a left sided tool-box (not on top), and a sealed driveshaft.
So I think you are very likely correct about a very early R50 although I still don't get how BMW and the VIN plate say it's a 1954 R51/3.

I am writing another thread to ask whether it matters if I buy R50 carburettors for it and it has an R51/3 engine.

Upgrading a plunger frame to swing arm frame means necessarily a new rear drive which requires a drive shaft rotating in the opposite direction. So also a new gear box was mounted without the manual leaver.

Cheers
Han Verhagen