My RT took a crap today...

[SWB]

Amazing. We don't even know what the failure is and the thread has taken a life of it's own full of spline failure rants. I'll go on record as saying up front (on another discussion board where thatman posted his failure first) that my guess would be NOT a spline failure. I won't be shocked if it is but my guess it that is isn't.

 

I recalled your comment earlier. Just for the record, this is in fact, yet another case of an early final-drive/spline failure.

 

And on it goes.. and on .. and on.

[Stan Walker]

I'm wondering if it's as simple as screwing up the guide pin and shaft alignment when the tranny is mounted. Or, if it's something more "permanent", like a poorly formed transmission or engine case casting, or the bushing installation where the drive shaft passes through?

 

We would all like to know that! I believe that it is the more "permanent" type but no evidence to support my belief.

 

Stan

[smiller]

I'm wondering if it's as simple as screwing up the guide pin and shaft alignment when the tranny is mounted. Or, if it's something more "permanent", like a poorly formed transmission or engine case casting, or the bushing installation where the drive shaft passes through?

 

We would all like to know that! I believe that it is the more "permanent" type but no evidence to support my belief.

I would tend to agree (that it doesn't seem to be a simple assembly error) if only because it seems pretty difficult to screw up the mating of the engine/transmission. As long as you don't get any large rocks in there I don't see what would prevent the surfaces from aligning correctly.

[Paul Mihalka]

One thing that points toward a "permanent" type of defect, most likely in the gearbox housing, is that when you have a early spline failure, and you squeeze BMWNA warranty hard enough, you get a new gearbox, not just a input shaft replacement in the old box.

[nrp]

I am a mechanical engineer - and many of you are dead right.

 

I have a 1975 R900/6 that stripped its splines at only ~20K miles, which was driven the same as my 1979 R1000 which

at 20K miles was still perfect. Why the difference?

 

I contend the wide variation in spline failure frequency is due to accumulated runnout errors from the manufacturing tolerances.

 

Another premature spline failure posting on another thread described a fixture he built that measured the runnout between the engine axis and the transmission input bearing mounting bore. It was about .005 inch, which is enough to cause a lot of fretting on a hign speed marginally lubricated (i. e. one shot of antiseize on assembly) spline.

 

Now look at the number of potential machining errors between the transmission and the engine. Machined parts that can be made in a single chucking operation can easily have pilot diameters that are essentially of zero runnout, just due to the process. The only errors are in the machine itself, and that is usually very small. However, parts that have to be remounted in the machining process, or which have difficult-to-measure dimensions are not so inherently accurate. Large parts (such as the clutch bell housing) that are stressed when mounted in a machine also have a way of coming out of manufacturing with errors due to chucking deflections.

 

In the BMW bike design, the alignment between the engine and the clutch housing is based on dowel pins - not something inherently accurate like pilot diameters. What's more, there are several points where errors could creep in. The design is really such that there are no alternatives other than a very precise manufacturing process. The process is not inherently accurate.

 

Maybe these accumulated errors happen to cancel, or just maybe they happen to add. In one situation you'll get excellent spine life, in the other you get a premature failure. The only thing certain is that any premature failure suggests an accumulated alignment error that suggests the need for frequent future spline lubes. The only way to find out the accumulated alignment error is to disassemble and look at the splines for condition.

 

Of course if any of the critical stationary parts are replaced, it becomes a whole new ballgame unless the everything is checked for alignment as was done on the other poster.

 

In summary - yes there are lemon bikes.

[Thatman]

Just wanted to let everyone know I picked up the bike today. Wow...my shifting before was much more difficult than it is now. Now it will basically fall into the gear where before I had push it into gear. Something I never noticed as it just happened gradually.