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BMW Design Flaws

those that have had the recurring and frequent failure issues have found that by careful measurement and relocation of one or more dowel pins (remove, fill and re-drill) that their failure issues due to misalignment were eliminated.
 
If it was only about misalignment, we would all see the same failure intervals, yet we don't.

While I agree that misalignment isn't the only factor, assuming that if it were only misalignment, the result would be similar failure intervals is incorrect. first off, it is safe to assume that every bike has misalignment to some degree in the crank shaft / clutch / input shaft interface. The more severe this misalignment is, the faster the splines will wear. When you work from one end of the clutch to the other, you see a whole lot of potential for misalignment:
  • clutch disc runout
  • input shaft runout
  • bearing runout
  • transmission housing bolt and dowel hole to bearing bore positioning
  • transmission housing bearing bore to mounting face perpendicularity
  • engine case bolt and dowel hole to bearing bore positioning
  • engine case bearing bore to mounting face perpendicularity
  • bearing runout
  • crankshaft runout
  • flywheel / clutch housing runout
  • clutch cover mounting face to clutch face parallelism

When you figure there are allowable machining tolerances for every one of these parts / assemblies which will stack together to cause varying degrees of misalignment on each motorcycle ever produced, you can expect there to be variations in spline life and lube requirements. Maybe the really short lived splines were on bikes where some of the machining was out of spec or where the spec was deviated in order to keep production going. Unless you have access to BMW's drawings and production records, you'll probably never know the full story. It is possible that the design was great, but the tolerances were never quite achievable in production. It could be that the design was compromised. At this point, it doesn't matter that much. BMW isn't going to fix it for us and it is up to each owner to decide how they want to deal with it.
 
There are 2 locating hollow dowel pins that align the transmission to the engine. The assembly technique has no options.
I'm speculating that the oilhead clutch housing is structurally weak and easily deformed - so much so that even if the two alignment pins are in place, spline alignment isn't assured. The clutch housing is a thin aluminum alloy die casting and has a major cutout for the starter.

The alignment problems may well be at the factory where the fixture for machining the raw casting allows things to be deformed while being machined. Next it may be a factory assembly technique where the clutch disk alignment tool isn't being properly used. Lastly it may be a field re-assembly error. Mixed in with all this is the factory's spline lube question itself.

The reason I doubt a casual machining error is that the clutch housing etc is most certainly made on a numerical machining center. These things are very accurate but only as long as the part isn't released from the fixture. It is especially suspicious that this problem has been ongoing over such a wide range of production years and would surely have caught BMW quality control attention via excessive warranty repairs.
 
There are no springs needed because the cushion is achieved on the input shaft inside of both the 5 and 6 speed transmission.
A quick look at the appropriate parts fiche will confirm this.
http://www.maxbmwmotorcycles.com/fiche/DiagramsMain.aspx?vid=51668&rnd=08102012

I checked the drawing. It does look like there is a spring right inside the housing on the 5 speed M93-M94 transmissions. I assume that does the trick. That, and the comment by Bikerfish that they aren't recommended means I will be getting the stock disc, if needed. Good. I usually prefer stock components, and in this case they are in fact cheaper. Interesting that RBS is another aftermarket company/repair shop touting the fact that they know more than the BMW engineers, and that we are fools to buy the German designed stuff.
 
I checked the drawing. It does look like there is a spring right inside the housing on the 5 speed M93-M94 transmissions. I assume that does the trick. That, and the comment by Bikerfish that they aren't recommended means I will be getting the stock disc, if needed. Good. I usually prefer stock components, and in this case they are in fact cheaper. Interesting that RBS is another aftermarket company/repair shop touting the fact that they know more than the BMW engineers, and that we are fools to buy the German designed stuff.
Besides - there is much more torsional compliance (which is good) in the gearbox spring system than there is in the alternate clutch disk model.
 
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