Frame/Engine numbers.

[yan1114]

I bought my R65 a few weeks ago and after her long hibernation(16 yrs) I got her up and running, I've done about 60-70 miles and I can't believe how well she goes! Now I'm not new to bikes, I've had lots and lots, I thought these smaller Beemers were supposed to be under powered! After my last ride I checked the engine number to see if it was a 750 or 800, I soon found a website to cross reference the R series numbers only to discover she's got a 450 motor, well bottom end, I can only assume there's been a bottom end failure at sometime, curiously  both engine and frame number are from the same year and month.

[jp9094]

Due to various regulations in Europe and the UK, an r 65 in 450 cc was marketed in those markets. That is obviously what you have!

FWIW,

[yan1114]

She's registered as a 650, maybe had a top end swap, I never knew the previous owner, he passed away and I bought the bike at auction, so nobody to ask.

[Kelvin]

The barrels are cast with their size, on mine the "6.5" at the base of the barrel on the upper leading edge indicates 650. Visible on this pic upside down. What do yours look like?

[georgesgiralt]

Enter your serial number into RealOem and it will tell you how the bike left the factory... If the engine number stamped on the oik dipstick is the same as the frame number, then the mystery will deepen ....

[yan1114]

Interesting, on RealOEM.com :-
 Frame number  R65  06/79 Type code 0353
 Engine number R45  06/79 Type code 0351
The two numbers are not the same, frame starts 634 engine starts 630.
I'll have a look at the cylinders for casting numbers when I get home.
Thanks for the help so far folks.

[yan1114]

The barrels are cast with their size, on mine the "6.5" at the base of the barrel on the upper leading edge indicates 650. Visible on this pic upside down. What do yours look like?

  Had a look at my cylinders, one has 6.5 the other has an A, I assume the 6.5 is on the lower side, I didn't have a torch to hand to look, so deffo a 650 top end on a R45 bottom end, I suppose a lot can happen in 40 years and 76,000 miles.
    Next job.....New back tyre.....Then investigate the Tacho/rev counter as it only moves up to about 1000-1500.....

[georgesgiralt]

Interesting, on RealOEM.com :-
 Frame number  R65  06/79 Type code 0353
 Engine number R45  06/79 Type code 0351
The two numbers are not the same, frame starts 634 engine starts 630.
I'll have a look at the cylinders for casting numbers when I get home.
Thanks for the help so far folks.

Mr BMW at the factory, install the same number on the frame and on the engine. So your engine was removed at some point and another one was put into the frame. It was not done by a knowledgeable professional otherwise, he would have erased the engine number and stamped the frame number into the engine. (engine have their own serial under the left cylinder, so stamping the frame number on it is legit if done properly and with the correct paperwork)

[Kelvin]

I'm more inclined to think that it's a bottom end swap (including the engine serial number) rather than the whole engine. For peace of mind I'd confirm that it has 32 mm carbs (R45 has 28mm) and that the final drive is for an R65 ("31/9" stamped on the housing near the shaft oil fill hole, cf. "35/9" for an R45 unit).

[yan1114]

Carbs are 32mm, can't find a stamping on the final drive, number under left cylinder not the same as engine number.

[Bob_Roller]

Congratulations !!!!
You have a 'frankenbike' !!!!!
Perfect for a Halloween cruise !!

[georgesgiralt]

Normal. the engine numbers are not related to the frame numbers. It looks like there was an engine production unit and that the engines where randomly picked up to assemble bikes.
IMHO, BMW numbered the engine to keep trace of variations or default in the making and be able to point the culprit if a warranty claim came. Gearboxes are also numbered. The serial is on the left side under the air box.  This is also normal given that Getrag made these and supplied them to BMW.

[yan1114]

Deffo 650