R100 oil pump question

I picked up a short block from a '79 R100RT to replace the blown engine in my '76 R90/6. While migrating pieces from one block to the other I found that the oil pump from the older engine won't work in the newer one. Instead of a round shaft with a slot for a woodruff key, the R100 cam end has two parallel flats instead (see the photo). So... the outer and inner rotors fit just fine, but there's nothing to drive the inner rotor. I'm new to Airhead rebuilding and would appreciate it if someone could tell me where I can find the right inner rotor. My local BMW dealer's parts guy wasn't able to help me, since his fiche showed the replacement rotor for the R100RT uses a woodruff key. Sigh...

Thanks in advance for any and all help.

Steve Mustoe
Eugene, Oregon

Not sure where to get one, but do you need #9 in this picture:

http://www.realoem.com/bmw/showparts.do?model=0393&mospid=47882&btnr=11_1973&hg=11&fg=35

The table indicates it's "from 9/1978". Try ordering it from your dealer or other BMW supply places - Bob's, Hucky's, etc. I just looked....Hucky's doesn't show it...

Thanks, but... the one indicated in the diagram still requires a woodruff key (and is identical to what I already have). What I'm trying to find is an inner rotor that does not have a slot for a woodruff key

Steve

diagrams not accurate

Remember that BMW fiche drawings do not always represent the exact part as it has been modified. Old parts drawings are often used, but you will note that there are several part numbers with qualifiers for various years. So the fact that a key is shown probably indicates that the drawing is for the early type oil pump with the key, and the second part number is the modified one.

Look, for example, at the 0-rings shown on the oil filters for many Airheads. The filters have had their end 0-rings bonded on since the mid seventies if not before, yet the original drawing showing separate 0-rings persists.

NB the key driving the oil pump was a wear point -- I have seen /5 engines with the key worn half away -- so the later square-drive pump is certainly an improvement you want to have.

I agree with CellarRat. The data indicates that a different inner rotor is used beginning with the '79 models, or from 9/1978. So, I wouldn't necessarily go by the picture. You need to see if the part number given and the actual part you see will work.

Thanks guys! I'll go by part number and not by fiche.

Steve