BMW R90/6 throwout bearing

Lots of new BMW parts!

Getting this very stiff rubber piece on the piston is tough!   I had to resort to using a small jewelers screwdriver for leverage to pry it on there and it still took about 15 or 20 minutes to get it on straight in the underlying groove.   Just keep at it you’ll get it eventually.

Here is what that blasted needle bearing looks like and the reason for all of this mess.   This is a bad design, BMW dropped the ball here.  The outside edge of these rollers will always try to spin at a faster rate than the inside edge causing these things to partially slide and slip along and eventually wearing out and turning to dust as I found out.

Previous versions of this clutch actuator design instead used a roller bearing with round balls, much better way to go in my opinion.  I have been thinking of a way to use the old bearing in my clutch, I think it can be done by just machining down the face of the piston and a bit of the end that contacts the adjustment screw to compensate for the thicker roller bearing.   More info on the differences and changes of the design over the years on this excellent website here.

With all the new parts assembled in my hands I now understand how this mechanism works, from the drawings I couldn’t quite understand what kept the end of the rod from drilling through the pressure plate (like mine did) without needing to be lubricated.   Now I see, when under pressure to open the clutch the whole rod spins freely (from the silvery bearing forward) and the piston remains stationary.

Like I mentioned before the washer on the end of the pushrod was fused to the shaft on one side and the other end mushroomed and flared out which made the removal of the old rod impossible from either direction.   I had to cut it apart to get it out.  Cue picture of sparks flying because it looks cool.

The aftermath:

I have heard several accounts on about using floss around the felt part to get the rod back through the transmission without it being removed.  So I decided to give it a try to see if I could do it for the future when I may need to do this..

Supposedly if you wind floss tightly around the felt (much tighter than in this picture) then you can squeeze the rod through without the felt coming off, then you just need to carefully unwind the floss leaving the felt intact.    Try as I might I could not get the @#$%^ floss to come off once inside.  I’m not sure if I was doing it wrong.

Looking at the old felt on the other rod I found it also had some string wrapped around it still, so maybe its ok just to leave the floss on.  It was a extremely tight fit even with the felt squeezed down with floss.

I also discovered that I had to put the rod through from this side as there was a ridge and groove inside the tube on mine which prevented it from being inserted from the other side, I have no idea what caused this, possibly bits from the old bearing when it cratered.

They say to lubricate this bearing when reassembling with lithium grease I believe, it gets lubricated with oil from the transmission which will wash the grease away once it is started up.   I didn’t want to go out and buy some so I used this Lucas Assembly Lube instead, great stuff.  Assembly lube is very tacky and will stay put while putting pieces together to give bearings like this essential lubrication on the first startup before they start getting oil on their own.  Should do the trick.


While the transmission was out I decided to do a fluid change and found this on the magnetic drain plug, a bit concerning.   I have read in many places that this much filings from the gears is “normal”.  I’m sorry but that much metal loss from anything should not be normal in my view,  regardless every airhead guy I’ve talked to and threads I have read on have said not to worry about it.

They say just to rub this in your fingers and make sure its a very fine sludge with no big pieces which could mean eminent bearing failures and expensive fixes ahead.

This is what I found, a few small flakes of metal inside all of that sludge.  The biggest piece is about the size of a sesame seed for scale.  It does look like bearing material to me, I don’t know if this means that I should get the transmission rebuilt or not.    My airhead mechanic friend says for that not to worry about it and  just ride.  “They will have a clunky shift like a tractor when new and they will still clunk when well broken in so don’t worry about it”  he says.

Ok….      I’ve put new fluid in it and slapped everything back together and the bike runs just as good as before the clutch broke so I guess all is well for now.

I will most likely send the transmission in to get rebuilt next winter or when I don’t have as much expensive projects going on at the same time just for peace of mind.  Almost everything on a BMW airhead can be fixed by the do it yourself mechanic at home but rebuilding a transmission I’d leave that for the professionals to do.



Fall Ride

We went for a nice ride today to get a picture for a scavenger hunt from the CC&D forum which ended up taking us into new territory that I didn’t know existed.  The fall colors of all the cotton woods and aspens were spectacular, quite a surprise.  The colors visible from Santa Fe up on the ski hill had already faded, they usually peak the week of Columbus day and we’d had an early snow which knocked all the leaves off.

We went from Glorieta to Pecos along the old Route 66 winding through the amazing colors and from there we came to a crossroads where I had no idea where we were or where any of the roads went.  We decided to head north and see where the road took us where we found a cool monastery and down a dirt road a lake surrounded by orange and yellow.

There were fishermen everywhere!  All along the road cars were parked on the shoulders and any little pullout and down in the river were fly fishers in waders and even more along the shore.   This guy had one nice catch and 4 smaller ones, he said someone had pulled a big one out just a week earlier.  Further up the road from the monastery lake was a fish hatchery, I bet they keep the waters around here very well stocked.


We saw several tiny tiny towns and some cool old buildings along the way.

Be sure to fill up ahead of time, highway 63 dead ends up the mountain and you have to back track to get down.  This old Conoco pump looks like its been dry a very long time.

Up at the very top was Jack’s Creek Campground.   Very cool!  Can’t believe I had no idea any of this was back here, this would make a good place to go camping close by.

Eventually we made our way to Las Vegas where we met up with my former boss and got some of his home grown squash!   Pretty awesome day for a ride.

BMW R90/6 Clutch

Just a quick follow up on putting the clutch back together after checking for damage and getting new parts in.

I am impressed that the OEM parts come in such heavy duty packaging. You don’t see that much anymore.

Siebenrock clutch disks come pre greased with something.  I went ahead and added a touch of Honda Moly 60 paste on top of this just to be safe.

  • If you have gotten the clutch apart as mentioned earlier reinstalling the parts is pretty easy, just reverse the process.   You will need this special clutch alignment tool, I got this one from Jeff Trapp at Northwoods Airheads.  Use the shorter end for pre-1981 bikes and the other end for post ’81 bikes when they changed the clutch design.
  • Simply install the long screws you used in removal to hold the assembly together while using the alignment tool to make sure all of the pieces are lined up properly. If things are out of alignment you won’t be able to get the transmission on later.

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