Problems

Corvus · Post by **Corvus** » Fri Sep 27, 2013 6:23 pm

Quote: "Are we ignoring tyre wear?"

I keep trying to.

But it just keeps coming back.

££££

Being all scientific though, if you're prepared to take it into account, you're working to closer tolerances than me.

Can't we just factor it in percentage wise?

Tapio · Post by **Tapio** » Fri Sep 27, 2013 7:36 pm

Corvus wrote: I was surprised to see ball bearings used. I thought bevel gears usually produce a substantial axial load? Unless I'm getting confused and another bearing carries this burden?

Ball bearings can carry thrust load too. There are angular contact ball bearings. Centreline in pics go through ball and contact points. Bearing on left can only take load in one direction, but the one on the right in both directions.

Corvus · Post by **Corvus** » Fri Sep 27, 2013 7:42 pm

Tapio wrote:
Corvus wrote: I was surprised to see ball bearings used. I thought bevel gears usually produce a substantial axial load? Unless I'm getting confused and another bearing carries this burden?

Ball bearings can carry thrust load too. There are angular contact ball bearings. Centreline in pics go through ball and contact points. Bearing on left can only take load in one direction, but the one on the right in both directions.

Hi.

Are angular contact used in this application?

I think even deep groove ball brgs have some capacity for axial load, albeit small in proportion to the radial load capacity?

Tapio · Post by **Tapio** » Fri Sep 27, 2013 8:17 pm

Yes.

Yes.

Corvus · Post by **Corvus** » Fri Sep 27, 2013 8:29 pm

Tapio wrote:Yes.

Yes.

Ah!

Um.

In that order.

fatnfast · Post by **fatnfast** » Fri Sep 27, 2013 9:34 pm

some good info on the FD and bearings here:
http://www.bmwra.org/otl/finaldrive/

Corvus · Post by **Corvus** » Sat Sep 28, 2013 7:29 am

fatnfast wrote:some good info on the FD and bearings here:
http://www.bmwra.org/otl/finaldrive/

Thanks for that.

Am i right in saying the assembly shown is from the first incarnation of paralever, used on the airheads? The large bearing behind the bevel wheel I take to be the angular contact ball brg mentioned by tapio? This would make sense as it would counter the taper roller brg on the opposite end of the shaft. Shimming being critical.

Frustratingly, it seems the assembly pertaining to the opening post is only briefly mentioned at the end? Have I got that right? They mention a needle bearing and ball bearing setup. I take it the needle bearing replaces the taper roller brg and the ball bearing replaces the angular contact ball bearing. By inference I take the ball bearing to now be a deep groove ball bearing? The other option would be a double row angular contact ball or pair of angular contact ball brgs, but this would be quite wide. I'm slightly confused on this last bit as I would find use of a deep groove ball surprising, given its quite limited capacity for axial load? However, if they found room for a double angular contact setup then this would be a decent solution in my eyes (not as if that would count for much!). Although even here clearance in the angular contact pair would be important, especially with regards to rear wheel play, but diminishing clearances due to expansion wouldn't really be a problem?

Maybe I'm completely on the wrong tack?

I apologise to anyone who has knowledge of this assembly from having worked on it. I apologise for my ignorance!

Corvus · Post by **Corvus** » Sat Sep 28, 2013 7:44 am

Reading it again, no mention is made of an angular contact ball brg and repeated reference is made to it as being simply a ball bearing. I take that to be a deep groove ball bearing. There's no wonder the damn things don't always last. It is a flawed design from the start and not made any better by changing the smaller bearing from taper roller to needle. Yes, this removes some loads off the large ball brg caused by the necessity to shim to zero when cold, but surely introduces all the axial loads, acting to the right, from the rear wheel? Barmey, on the face of it. Ok, space is at a premium and so you can't always fit in the best arrangement.

I stand to be corrected.

fatnfast · Post by **fatnfast** » Sat Sep 28, 2013 9:45 am

Yes, its just a caged ball bearing and your right in that its of a deep grove construction. I would agree that it is a somewhat flawed design from the start and would easily have its life reduced by incorrect shimming. From various threads on other sites it looks like its fairly common for the cage holding the bearings to fracture which then leads to total failure.
Strangely enough I ran a K100 for many years and miles and never had a problem, which seemed to be the norm for any K bike. I guess this points to the way the Rs deliver their power being twins?
Some folk treat it very much as a consumable which they replace every 30k or so.
I would imagine that the way, and where, the bike is used was also contribute to early failure. It wouldn't surprise me if there were more failures in the GS series than the other beemers that use this set up.
The picture looks just like the internals of my 1150gs.
At least its pretty easy to change and still cheaper than replacing a set of chain and sprockets

Tapio · Post by **Tapio** » Sat Sep 28, 2013 11:24 am

What I meant was; there’s thrust load, thus angular contact in brgs. What the bearing looks like, I don’t know. Will soon find out, hopefully. I’m off to the garage now. I have a FD lying around there. I’ll take it apart and see. Will take pics.

//T

Tapio · Post by **Tapio** » Sat Sep 28, 2013 3:02 pm

Taken it apart now. Bearing is FAG 61917 c3. Not an angular bearing. Mind you, the FD is from a K 100 ’90, but chances are, the design and the bearing is still the same.
It was way past expiration date. Tapered bearing was ok, as was wear pattern on pinion and crown wheel. Fd was run for 100 000+ km.

Corvus · Post by **Corvus** » Sat Sep 28, 2013 4:32 pm

You can imagine that there is a lot of pressure on the designer(s) to save on unsprung weight and come up with a compact and aesthetically pleasing result. Can't be easy. Lots of compromises I guess.

On the later designs, the ones with the hole up the middle of the wheel, I wonder if the pinion is overhung? To make way for the larger outboard bearing on the final (hollow) shaft?

Can't help thinking that thrust loads in both directions could be supported by a pair of taper rollers or angular contact balls on the outboard end of the output shaft. Leaving the large ball bearing behind the bevel wheel free to look after radial loads only. Make the pinion an overhung design, freeing up space to achieve that. Easy to comment from the armchair!

Corvus · Post by **Corvus** » Sun Sep 29, 2013 10:43 am

Tapio wrote:Taken it apart now. Bearing is FAG 61917 c3. Not an angular bearing. Mind you, the FD is from a K 100 ’90, but chances are, the design and the bearing is still the same.
It was way past expiration date. Tapered bearing was ok, as was wear pattern on pinion and crown wheel. Fd was run for 100 000+ km.

Took me a while to track this catalog down, but this should explain a lot of things for anyone interested. Not bedtime reading!

http://www.phufart.pl/_struktura/katalo ... TAWOWE.pdf

Steptoe · Post by **Steptoe** » Thu Oct 17, 2013 4:44 pm

You must heat the bearing up so it drops on the output flange.

Then you absolutely must heat up the final drive cover, and drop the bearing and flange into it.
You must not "knock" the bearing/flange into the final drive cover.