so upon first sight of the new K100 I noticed a leak at the rear drive. I was told it may just need a new crush washer, but having just refreshed the oil there and replaced the washer, I still get the oil dripping down the inside of the drive, onto the brake disc, and pooling on the wheel!!!  


So the Haynes manual said to fill it to the inside most threads of the filler cap, but that it shouldn't touch the bottom of the filler (how you know that with the damn filler on I have no idea!!)  It said if overfull it would come out the overflow tube. 

now you don't suppose this is overfilled and just coming out the overflow (where is the overflow anyways?)  or do I have seepage around my drive cush?

The usual suspect for a final drive leak is a drip of oil onto the floor from the bottom of the unit or where it joins the drive shaft, not from the top of the final drive unit. 
Take the filler plug out again and with a torch peer down into the fill hole. The oil level should be just touching the bottom of the screw thread. Sounds to me like it is overfull and forcing out the breather cap.
Good luck

no, it seems to be coming either from the lower drain plug or the inside of the unit, between the wheel and the drive...

more than likely the output bevel drive seal .(fits right near the bolts of the housing to wheel mount shaft )

easy fix .....you can buy the right seal almost anywhere ...

don't forget to linish up the main output shaft a little bit to let the new seal bed in properly
looks like I have to do mine again pretty soon ....(might have to check that output bearing whilst im at it too ...though cant see any movement so far )

Well seems like I might be in the same boat just a little smear of a leak around the seal.
Let me know what part you order charlie so I don't make a mistake with mine and snowbeard can be happy he has set us off on a mission.
I'm not doing mine till it gets too hot to ride, have to get a big trip in before xmas.

Take the wheel and disc off the back and have a look at the big seal behind the disc that is most likely where it is leaking. The breather is right at the top of the drive and you need to have a lot in there for it to come out there and you will see it all over the outside of the drive.
Take care with the 2 countersunk socket head bolts that hold the disc on the may need heat to release the loctite.

If you do need a new seal, buy a new O-ring too. They often need replacing once they're disturbed.

aye indeed mike !

great advice, glad to hear its not too big of a job!  

So Charlie, if you have a part number, or a good online source I'd love to hear it, for the seal and the o-ring (?) that Mike mentioned? 

Also, what was that about "linish" up the main output shaft a little bit to let the new seal bed in properly


I assume linish is a typo but I can't imagine what you meant? lube? finish? line up?  


Thanks!!!

Hi Snowbeard, 





From Wikipedia......


Linish is an engineering term that refers to the process of using grinding or belt sanding techniques to improve the flatness of a surface. The flatness may be two-dimensional, i.e. with the view of achieving a flat plate, or one-dimensional, e.g. with the view of achieving a perfectly cylindrical shape. The machine that does this may be called a linisher or a linish grinder. The technique may also be used, with finer grades of grindstone or sanding belt, to polish a surface.

Mike

oh, don't I feel silly now!  

so is this something safe to do by hand with just a piece of 1500 grit sandpaper?  are these drives often not finished cleanly enough?

Snowbeard - Yes and Yes,  it is recommended to clean off any residue or crud which may be on the shaft.

hi snowbeard

the linish process is to
1> take off the sharp edge where the old seal has been running into the metal (soft things wear hard things ) and will form a groove of somewhat pitted appearance  ...this could damage the seal edge of the new seal if left intact, either by the installation process ...or further long term wear in the same location

2> clean up the shaft across its length towards the installed position of the seal ....this will remove crud that accumulates (often over years of being exposed to the atmosphere and all the rest of the things that corrode metal things )

all that is necessary is to get a strip of  wet and dry (fine grade ) maybe 1 foot long by about 1 inch wide and use it in a manner of wrapping it partially around the shaft and using a pulling motion to kind of seesaw  the material back and forth

maybe worth mentioning that that shaft is really hard material (possibly heat treated for case hardening ?)

you might have to do the process with several strips of wet and dry to get a good finish

ill look up the seals guys ...

the outer seal around the bevel box housing is a fairly standard o ring ....(just need the right length and diameter )

the big shaft seal is another fairly common size
from memory ..the original is 10 mm thick ...although the local guys stocked a 12 mm one which I got ....advised by the bearing guys that it would be safe to cut off a small area on the inner part of the seal face (away from the seal side ) which brought the dimensional width back to about 10 mm  and lined up with the seal housing edge  and depth

I posted my refurb in here some where ....a while ago now ...maybe 2 years ...ill go have a look and see what I can find ...

back soon

link for some pics .....theres more out there somewhere
https://www.k100-forum.com/t1833-85-rt-resto-my-attempt-hey-im-not-into-making-a-show-bike#16702

the housing seal o ring is  171 mm  by 2.62 mm thick ...so easy to find

the shaft seal  is 85mm x 110mm x 10 mm  
sorry don't have the part numbers that I bought
but look for the ones that have some form of nitrile component in the seal for long duration oil and heat resistance


or have a look in this same section (bevel drive ) for the parts listings
http://realoem.com/bmw/showparts.do?model=0504&mospid=51753&btnr=33_1565&hg=33&fg=76

hope that helps

Hi snowbeard,
Just a tip.
 If the seal bearing surface is pitted and won't clean up by linishing, fit the new seal slightly proud (say 2mm) of the casing so that the seal lip runs on an unworn section. 

Paul.

It it was factory installed, getting the rear brake disc off can be a hassle.  Between the uber-Loctite the factory installed those two bolts with and a little corrosion over the years those can be a bear to get out.

Do it before you take the final drive off so you can get some good leverage on them. Heat them lots with a torch, use a GOOD Allen wrench (like the one in the factory toolkit) and pray.

Even then the Allen head may strip so be prepared to drill the heads off.  If you do it carefully then there's plenty of threads left so you can use Vise-Grips to get the rest of the bolt out.

When I re-install them I use anti-seize in case I ever need to remove the rotor again.

+1 duck, also they don't need to be tight, they're only there to hold the disc for assembly and when the wheel is in place they can't come out anyway.

Paul.

Thanks Tons!! That really helps and I find a few seals using the RealOEM site to have part #33121241938. I can find this on some sites as well as Ebay so I will order it and go forth  




may as well do  the spline lube while I'm in there, and hope I can get those pesky rotor bolts out  :-/  

so I just want to be sure that I'm ordering the right part here, it came up with the part number I found from REALOEM, but the seller doesn't list it as K100, only R100... it has the dimensions that Charlie specified so I'm assuming its correct... ?

http://www.ebay.com/itm/BMW-Motorcycle-R65-R80-R100-Differential-Shaft-Seal-33121241938-/171096634233?pt=Motorcycles_Parts_Accessories&hash=item27d6277379&vxp=mtr

Thanks tons!

Oh!! that's a great resource, didn't realize I could do that!! 

bit expensive

I got one out here for $15.00

non genuine

That one is a directional seal and for $15 I will bet my leftie that yours wasn't.

rick, are you talking to Charlie or me?  is this one I linked to good?

thanks!

Sorry mate, the one you show is the best to use as the cheaper seal won't have the directional serations on it.
If you look at the picture of the seal you listed you will see on the inner lip serations that go counterclockwise to the inside that helps keep the oil away from the seal lip so it doesn't have as much to deal with.
The $15 one Charlie fitted would do the job but probably wouldnt last as long and that was what I was betting my leftie on (safe bet considering it aint worth much nowdays).

cool, thanks for the clarification!

As I always say "I'd give my right arm to be ambidextrous"