non-matching serial for R51/3

[Scott Wilkinson]

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

[Bruce Frey]

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

[Scott Wilkinson]

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.

[Brue Frey]

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

[Scott Wilkinson]

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

[stacey]

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)

[Scott Wilkinson]

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.

[Han Verhagen]

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