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Franklin, please share the circumstances that led to the failure! I wouldn't want that to happen on a stormy night 200 miles from nowhere.
 

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Discussion Starter · #4 ·
2005, K1200S, with 7500 miles.

As I understand it, it's not the speed but the amount of torque applied to the shaft.
Wacking the throttle open from the light will twist the hollow shaft like a pretzel.

Franklin
 

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Francois5200 said:
2005, K1200S, with 7500 miles.

As I understand it, it's not the speed but the amount of torque applied to the shaft.
Wacking the throttle open from the light will twist the hollow shaft like a pretzel.

Franklin
If just hitting the gas hard is twisting the shafts, I wonder how many drive shafts out there on the road may have some amount of torque twist in them right now?
Probably no need to get alarmed yet but, this is something we should watch closely.

If this is accurate, then I'd say BMW needs to issue a service bulletin and replace them all with a stronger drive shaft.
 

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Francois,

I hope this is not a real issue. I don't think it is since we have heard nothing about it. That said, I never "pop" the clutch from a dead stop; I always start rolling for a second or so and then wack open the throttle. These roll ons probably are less stressful on the drive train. I've never experienced a problem riding this way (with a K75S, R1100RS, K1200RS or the K1200S).

Ken
 

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Make them call it what it is....

That shaft should not be hollow. Weight does not seem to be a factor with that bike, so what gives? Looks like Beemer has gotten caught with their shorts down........ again! Poor design! Wonder what type of shaft is in that Bavarian Beast that they advertise?
Ride that Beemer, don't let it ride you...
Murph
 

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bmwknight256 said:
That shaft should not be hollow. Weight does not seem to be a factor with that bike, so what gives? Looks like Beemer has gotten caught with their shorts down........ again! Poor design! Wonder what type of shaft is in that Bavarian Beast that they advertise?
Ride that Beemer, don't let it ride you...
Murph
I may be wrong but I think that a hollow shaft is stronger than a solid one in terms of resisting torque forces.

After all prop shafts on cars are all hollow. Against that the drive shafts from the differential to the driven wheels are not AFAIK.

Any engineers around care to comment.
 

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Most of the load is carried on the outer portion of the shaft so a solid interior is just dead weight, ie hollow = the right design. Figure maximum torque transfer, throw in a safety factor, pick a material for strength ... calculate preferred diameter and wall thickness.

Now IMHO the subject case is either a production line defect (rare fluke or questionable QC), BMW are minimizing their safety factors for the sake of saving weight (Formula 1 influence), or somebody miscalculated. Take your pick. I favour the rare fluke because this defect hasn't shown up on the Powercup bikes or Press workhorses where 'gentle' isn't in the vocabulary. Time will tell. Although this shouldn't have happened on an unmodified production unit, at least the shaft deformed and didn't break (very bad).
 

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Um, this may be a stupid question, but how did you know the shaft was twisted?
I mean, just because it's twisted doesn't mean it won't turn in the housing.
Lenny
 

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Discussion Starter · #11 ·
Lenny said:
Um, this may be a stupid question, but how did you know the shaft was twisted?
I mean, just because it's twisted doesn't mean it won't turn in the housing.
Lenny
Good question Lenny,

You are correct. It did turn in the housing, but I knew that there was something wrong because I could feel a slight rub, rub, rub, rub as the bike moved.

After seeing the shaft yesterday at the shop, it was obvious that though twisted almost perfectly, it was no longer true and was rubbing against the shaft housing.


Franklin
 

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Maybe if you refrained from clutching up wheelies with fat chicks sitting on the handle bars this wouldnt happen!! LOL
I would think this was a singular metalurgy style problem as someone said above there are alot of the drive lines out there getting heavy abuse with no failures.
 

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zzrman said:
I may be wrong but I think that a hollow shaft is stronger than a solid one in terms of resisting torque forces.

After all prop shafts on cars are all hollow. Against that the drive shafts from the differential to the driven wheels are not AFAIK.

Any engineers around care to comment.
Hollow drive shafts are common for good reason, they are lighter or stronger than solid shafts. Comparing two shafts of the same weight, one hollow and one solid. the hollow one can be made with a larger diameter and it will carry more torque than the solid, smaller diameter shaft. Comparing two shafts of the same diameter, one hollow and one solid, the solid will carry more torque but will weight more.

Ron
 

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Discussion Starter · #14 ·
"Racing" Cardan Shaft

I found this Adobe pdf document on the K1200R forum. It's the Technical Regulations of the BMW Motorrad Power Cup 2005.

http://www.bmw-motorrad.co.uk/com/e...ascination/motorsports/powercup2005/home.html

Click on the link that's titled "technics."

Page 4 of this document contains a list that's called "Racing Kit." One of the items in this racing Kit is what they call a "Racing Cardan Shaft."

The "Race Cardan Shaft" is mentioned again at the top of page 10 in the section that describes the rear wheel drive.

I don't want to jump to conclusions here, but it looks to me that the Power Cup Bikes get a stronger shaft.

What exactly is a Cardan Shaft? Is that a general description of the type of shaft that's in our bikes, and a "Race" version of that is in the Power Cup bikes?

I'd like to know what other's think.

Thanks,

Franklin
 

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Solving the clutch problem

Wouldn't the clutch slip before this piece would fail if this were a design problem? Seems early to assume this is a design problem rather than a unique situation. Either that or they really did beef up the RS clutch! Curious failure.

Velomaxx
 
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