What could cause a clutch to break like this...?

I had a problem with my bike not getting any power to the wheel, took it into the shop, and then when I went in to see if they had found the problem, they said that it had broken. Apparently the arms that hold the center of the clutch plate where the splines fit in, are no longer attached to the outer portion of the clutch. It all came apart apparently. Here's a picture of a clutch plate I borred from Hassenwerk, modified to show where the clutch plate came apart. Note the red lines.


How can something like this happen? The clutch has only about 6K miles on it.

Is the gearbox all right? is the bike used for heavy offroading or stunting?

Stewart

No stunting, I have been off road, I did the first half of the White Rim trail in May, just like a half day in and then back out. Nothing I would consider to be hard on the bike. The wheels never leave the ground or anything like that.

I believe the gearbox is good, haven't had any problems getting into gear or out of gear.
edit - Other than the regular finessing that comes with a GS.

That area is designed to slightly flex and absorb harmonic vibration.
make sure your brakes are not dragging firstly, after that i think could only be improper adjustment. likley too much travel when disengaged (lever pulled in) causing overflexing. is it also possible that it could have been installed upside down? if the input splines have a similar height on each side but not exactly the same? not an expert but i have seen this very type of damage on autos with seized brakes, good luck

I seem to recall reading somewhere that the motor and gearbox on some bikes does not line up properly and can possibly cause this type of problem, were the bolts all snug and any dowels in place ? either that or a problem with the metal of the clutch hub, does the wear on the plate seem normal for the miles ?
Stewart

Well I'm sure I'll find out soon, they are going to see about a warranty replacement because the clutch is so new. Either way, it's gotta be replaced.

Ask the shop to check for excessive rear main bearing wear, They can do this without disassembling the engine by gently prying the flywheel in different directions while measuring the flywheel motion with a dial indicator. The clearance measured this way at the flywheel should be only maybe .003 inch in any direction. The engine specs say .002 inch at the main bearing but of course the flywheel is outside the bearing set.

A skilled mechanic for that matter could even just get an idea of the bearing slop in a couple of minutes just by feeling the motion of the flywheel. Be sure to check it in a couple of directions.

If there is a serious engine-to-transmission alignment issue, the result can be wear on the rear main bearing. Once that bearing gets sloppy, the firing pulses of the cylinders will have to be reacted by the transmission input bearing rather than the main bearing. At that point there would be a lot of radial fatigue in the clutch spider (that's what it is called).

Looks to me that the clutch did not slide on the splines of the shaft.

Check the shaft and splines.

I guess since the clutch is toast, they are going to have to replace it anyway, so when they have it off they can check out the splines etc, and then the alignment of the engine and gearbox, they would do all of that as a matter of putting it all back together wouldn't they?

What happend to the old one? Did it die from normal wear? Could the new one have been improperly installed? Just wondering.

Can you get pics of the actual clutch plate?

So anyway... All turned out well. The clutch was relatively new, only 6K miles on it, so the shop replaced the whole thing, parts and labour, under warranty. I was very impressed with that. I didn't get the plate back, they had to send it away for the warranty. Didn't manage a picture of it either, didn't have my phone with me. I saw it though, and the lines I drew in the picture above aren't really in the right place. They should have been further inward, towards the shiny circular metal bit with the 8 bolts in it. The break was more of a circle that went around that center part.

I truly hope this is the last chapter on this.....

What more could go wrong?

Did they give you an explanation for the failure?

I had an identical problem on my '06 1200 ADV... actually, I broke the clutch THREE TIMES before they realized the problem was in fact elsewhere, and the broke clutch plate was just the effect of it.

In my case, they had to replace the entire gearbox shaft, that was out-of-tolerance and therefore producing excessive vibrations.

Damn, I hope that's not the issue. They didn't have an explanation other than to say that there was a defect in the clutch plate. They have had the trans out of the bike a couple of times in the last year but have never mentioned that the gearbox shaft. Is that another word for the input shaft?

I'd guess that the rear engine main bearing is loose for whatever reason and that the alternate firing pistons (from the boxer engine) are fatigue loading the clutch plate spider.

The rear main bearing may be loose in the transverse axis because that happened to be the direction of radial misalignment of the transmission axis with respect to the engine crankshaft. This could be checked with a dial indicator by removing the starter and measuring the crankshaft backlash motion with a moderate prybar force while the clutch is held disengaged.

The main bearing clearance should be only a couple of thou, but if it is much more, the alternating piston forces are being reacted not by the rear main bearing, but thru the clutch disk, the clutch spider, the spline, and into the transmission shaft input bearing.

Just a theory, but it is easily checked.

Good lord. That sounds terrible. :eek1

I will share this info with my mechanic at the shop though. Thanks! :)

Yes, exactly!
(you have to forgive me for my english, it's not my mother tongue...)

Anyway, my long story short:

I broke my first plate while riding around my town. Same outcome as your: clutch disc literally torn apart with no apparent reason. The bike had nearly 7.000 km at the time.

They replaced it under warranty, blaming a defective part. "Shit happens" they said. :huh

But after another 6.000 km or so, I broke it again.
This time they replaced the entire clutch assembly, saying that there "probably" was a problem with the flywheel (sorry, not sure about the word...in the picture below, it's the upper-right disc. Don't mind the writings... )


So they replaced everything and all was fine until it broke AGAIN 6.000 km later, this time in the middle of the Ruta 40, in Patagonia!! :eek1

Back in Italy, the bike was disassembled for the third time and THIS time they finally found the problem: the two parts circled in the picture below (sorry, I not sure about the english name for them... "dumpfer" maybe?) were slightly out of tolerance and were generating too much vibrations on the input shaft. The result of these vibration was the failure of the clutch plate.



They replaced the entire input shaft assembly and I finally rode more than 10.000 km without further problems:



Then I sold the bike for the 2010 model!

No way. There would be many other things going on besides a broken disc.