OMG! We Have TINY (Spline) Shafts!

[dnat928]

With the continuing saga regarding the clutch spline shafts, I was inclined to take a peek at mine. I have been a regular reader of the various topics relating to those that failed, those with wear and those still clean and sharp. Intriguing was the topic that provided a way to look at the spline shaft by removing the starter. Last weekend's oil change got me into the cycle-work mode. Removing said starter, there it was. And to my amazement - it was TINY! I was shocked and emmbarrassed!

Apparently, all those posts about spline shafts - with photos - were CLOSE-UPS, giving me the impression that our shafts were BIG. OK, as a mechanical engineer, one look was all I needed...no doubt, these things are way too small, aside from all the other issues on lube and alignment.

Just to get a feel for possible wear, I did the clutch-play exercise to see of there was a growing gap between the spline components. Per the thread, play of about 1/8" at the outer edge of the clutch plates was nominal/low. My check showed that or less. Also of note: those photos of failed splines seemed to have a fair amount of iron oxide powder in the vicinity of the splines. One thread noted that upon loss of lube properties, oxidation commences - and iron oxide powder is itself an abrasive, hastening wear on the spline surfaces. Of note - there was no iron oxide powder in the area and my spline was shiny. A dental mirror check saw no undue wear or indications of wear. I feel better now, but a full disassembly and lube is still somewere in the not-to-distant future...now at 49k miles.

[AndyRR]

I had the same reaction when I first saw the splines in person. I should have given it some scale before. If your measurement was at the toothed edge of the flywheel, you have about 1.5 degrees of backlash. If I am reading you right, you measured 1/8" at the edge of the clutch. With an approx diameter of 164mm that gives you about 2.2 degrees. My splines had not yet failed and were at 5.1 degrees.
I was about to suggest that you take a closer look before spring gets here, but then I noticed your location. Nevermind - ride it.

[NoRRmad]

GadZ! Considering that about 85 pounds-feet of torque goes through that.. That is tiny!

[Beemeridian]

11

[cricman]

"U.S. Currency
The Counterfeit Detection Act of 1992, Public Law 102-550, in Section 411 of Title 31 of the Code of Federal Regulations, permits color illustrations of U.S. currency provided:

* The illustration is of a size less than three-fourths or more than one and one-half, in linear dimension, of each part of the item illustrated

* The illustration is one-sided

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[AndyRR]

fixed

[NoRRmad]

[Beemeridian]

=11

[awagnon]

OK, as a mechanical engineer, one look was all I needed...no doubt, these things are way too small, aside from all the other issues on lube and alignment.

Not only are they small, but they only engage the clutch splines by about 2/3 rds which makes their effective size smaller. I assume as a mechanical engineer, you wouldn't have made them too short either.

[sweatmark]

The extended spline shaft option is intriguing:
http://www.advrider.com/forums/showthread.php?t=301863
Project initiator GSaddict states that he received deposits for only 2 input shafts.

Mech.engr. 6th sense (hex-sense?) is telling me that Mrs. Sweatmark's 26k miles Roadster has some sick splines that will need TLC this season. My 15k Rockster is still too young for regular spline-oscopy, maybe next winter.

Thanks to AndyRR for the great pics and troubleshooting references in his thread.

[awagnon]

The improved ( ie, long splined ) input shaft has been discussed on various forums for over a year. To my knowledge, no one except the guy that makes them has gotten one. At first he needed five orders to justify a production run. Now it's 10 and he still hasn't sold any. I would have purchased one when my splines failed last winter, but he wasn't making the new shaft then, either. Even if he did manufacture them, there is still a question whether the new splines will still fail if there is a significant misalignment between the shafts. Perhaps it will just last 1/3 longer since more of it engages the clutch plate.

[Sunbeemer]

I thought the same when I saw a picture of the shaft being pointed to with a pencil eraser, and thought it must have been a photographic illusion - I couldn't believe BMW would under-engineer such a stressed member.