Unusual engine number.

[Deleted account 111026]

Started to strip my cafe racer donor R100RS today in readiness for powder coating the frame, etc. The frame number is: 608**** which, from www.bmbikes.co.uk website, means it is a July 1977 bike.
The engine number doesn't match the frame. It is stamped at the dipstick hole, as per normal, and has definately not been modified. The number is:
2946425.
French logbooks do not show the engine number so no information there.
This number doesn't appear to relate to any standard engine range.
I decided to remove the cylinder heads and barrels to investigate further and have found the correct 44mm inlet valves but the welcome plus of Nicosil barrels!
The ignition is still points, not electronic.
Has anyone any idea of how I can date the bottom end or has anyone seen an engine number like this before?
Perhaps the bike has had a factory exchange engine unit at some time in it's life?
The previous owner had the bike for over 10 years and he assured me everything is as he bought it.
If it is a later engine I will be pleased as the 336 camshaft is no longer available for the 1977 models!

 

[Kenny]

My bike is in hiding at VNDprojects at the mo but I'm sure the engine number is stamped at the base of the engine

Nicosil..way to go

 

[Deleted account 111026]

There is a number stamped at the base of the left-hand side of the engine, 823610, unfortunately this doesn't relate to any listed engine numbers.

 

[(RIP) Proff]

Dipstick number is casting number
Engine number lower down


Take a closer look at the number, should be a 6 to start, but kraut 6's look like 8's

 

[Deleted account 111026]

This is getting more confusing
I also have a 1977 R100/7, the frame and engine numbers are identical, the engine number is ONLY stamped next to the dipstick, the plain face on the bottom left of the engine is unstamped.
On the R100RS, the number on the bottom left of the engine, which you believe could be the engine number is only 6 digits, not 7, plus it definately is an 8, not a 6, the number '8' is 'waisted' whereas the left-hand side of the number 6 is a straight line.
I've never had an airhead before where the engine number has not been easy to locate, or date!

 

[brassmonkey001]

Mine is stamped:
**/**/****
***$$
Where *= a number and $= a letter.
I've no idea what it originally came out of or when it was built.

 

[Deleted account 111026]

Thanks for that, I think I'll strip the complete engine rather than just the intended top-end overhaul and check and list everything that's there.
At the end of the day, it is 31 years old and anything could have been changed during it's lifetime.

 

[Rob Farmer]

If you assume the engine and frame numbers should match and put them into realoem you get this http://www.realoem.com/bmw/select.do?vin=2946425&part=&kind=P&arch=0

It flags up as an October 1972 R60/5. This cross references with BMBikes website.

Have a look at the date codes inside the covers, airboxes and other parts to see if theres any common dates appearing. It looks to me as though somebody has rebuilt the engine, for whatever reason, using earlier crankcases. The later barrels are a bonus.

 

[Steptoe]

Dipstick number is casting number:
Engine number lower down


Take a closer look at the number, should be a 6 to start, but kraut 6's look like 8's

Not so - engine numbers were on the dipstick hole up until 1984. Then they moved to the bottom lower left on the engine case.

 

[MikeP]

Not so - engine numbers were on the dipstick hole up until 1984. Then they moved to the bottom lower left on the engine case.

My mate's 1979 80/7 engine number is still next to the dipstick. How long should it take to migrate to the bottom lower left?

 

[Deleted account 111026]

Rob - thanks very much, everything now makes sense! I've been inside the engine and all the internals are as per the 1977 date for the cycle parts, I'm inclined to agree that at sometime the crankcases have been changed, (and the barrels and pistons).
I'm not concerned as everything appears to be in good order, it's good to be able to discover a bit of the history of a bike!
(If the engine number starts sliding down the casings, I'll let you know!).
Thanks again.

 

[(RIP) Dennis]

All very interesting, but I still can't find a number of any description on my 1995 R110GSPD !!!

Anyone any ideas wherelse I should look?

 

[Steve]

All very interesting, but I still can't find a number of any description on my 1995 R110GSPD !!!

Did you buy it from Kenny?

 

[Wreford Miles]

It's when I read threads like this I realise that although I own an Airhead I'm not really an Airhead owner.

When I know and care about engine numbers, I'll know I've become one - well that and the fact that that people will start pointing at me and saying that man smells of wee.

 

[Mick13]

In 77 normally engine and frame are matching numbers
If you put your engine number on a internet win decoder, you find what ?