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Old 15 Dec 2006
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Exclamation BMW circlip thread, please contribute!

Hello. I've copied this thread from the Advrider forum. I would apreciate everybody's input

Hello. I would like to start a new thread on the BMW circlip issue. I responded to a previous post: http://www.advrider.com/forums/showthread.php?t=188328 ... i stated that the circlip saves the bearing if the shaft isn't shimmed properly. I was corrected by Anton Largiader, who posted some very informative photographs showing the output shaft having slipped away from the bearing shoulder. (Thanx for the photo's Anton! :clap ) Since then i've delved deeper into this issue and i have a few questions: First of all, if you have the circlip installed, what stops the entire bearing from pulling out of the housing and causing the same linear force? I supose that if the shaft were allowed to slip out of the input-side bearing, it would transmit all the force to the bearing on the shaft side, but with a circlip installed, maybe it divides the load between the two? Is installing the circlip the answer, or is the transmition destined to fail regardless of what you do due to bad design? What if the out-put bearing was changed to a thrust- type bearing?
Ultimately, i,m curious what changes did BMW make to the oilheads to eleviate this problem. Is it the helical angle of the gear, better bearings, stronger housing? Lets amagine for a moment someone (like me ) had an oportunity to play around in his garage and build a new airhead transmition from scratch, what would you do diferent to solve this problem? Do you think it's posible to use the oilhead gearbox internals inside a custom airhead housing? From what i can tell, they are basicly the same idea, just improved gears, bearings and a diferent housing. I would like to here all your opinions on this subject, and maybe we can together create the ultimate airhead transmition :freaky
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Old 16 Dec 2006
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Interesting link with good photos. I was one of those unfortunate guys where the bearing slipped off the shaft due to the missing circlip. With the result that the gearbox had to be overhauled :-(

To my knowledge only the production line between Jan and Aug 1993 was done without the circlip. After loads of complaints BMW returned to securing the bearing with the clip.

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Old 16 Dec 2006
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I agree, the photo's in that link are excellent, but i'm still not convinced this solves the problem. This is my point of view. To install the bearing, the back side of the case must be heated because the bearing has a slight interference fit when the housing is cold. But when your up to operating temp., the housing will loosen it's grip on the bearing, right? So what's preventing the bearing from shifting in the housing causing the axial load on the large output bearing? Hmmm....
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Old 16 Dec 2006
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Talking

My airhead gearbox (with circlip) is still not opened at 180+kkm and I have witnessed more problems with the gearboxes on oilheads then airheads…
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Old 16 Dec 2006
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Really!?! Ali, plase tell me what you know. Since i got into this BMW thing four years ago i haven't heard a thing about oilhead problems, other than the cases breaking where the footpeg attaches.Please elaborate, or send me a link if you can
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Old 16 Dec 2006
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Mr. Ron,

unfortunately I can't be very specific about details, because I had it done at a good small Beemer workshop, not an official BMW dealer.

As far as I know, the bearing is pressed onto the shaft and additionally secured with the circlip. Mine was originally supposedly fixed by some special glue - which didn't work as we see. At 18,000 k's it came off. So the groove for the circlip was machined on the original shaft and since then I've done 90,000 k's without any further mishap.

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Old 22 Dec 2006
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Quote:
Originally Posted by Mr. Ron
This is my point of view. To install the bearing, the back side of the case must be heated because the bearing has a slight interference fit when the housing is cold. But when your up to operating temp., the housing will loosen it's grip on the bearing, right? So what's preventing the bearing from shifting in the housing causing the axial load on the large output bearing? Hmmm....
Possibly the large bearing will also 'foat' with the heat ?
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Old 17 Feb 2007
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5th Gear is culprit

The 5th gear is the cause of the bearing being pushed of. This gears helical design add a lateral force against the bearing and pushes it of. I have even seen cir-clips being pushed of together with the bearing.
BMW have the solution with the new output shaft bearing. This bearing is not standard but have a sharp edge on the one side of the inner race as it fit on the shaft. This area must face outward when the bearing is installed and a new cir-clip fitted to sit flush on this area. The smaller rounded clip that was fitted underneath the cir-clip on the standard type bearing is omitted.
Most gearboxes are repaired without this bearing as it is about three times the price of the standard bearing bought from the local bearing supplier.(and most people does not know of it's existence.) I know dealers that use aftermarket bearings to do repairs.
This small saving in the cost of the bearing is not worthwhile, just fix your box using the genuine part.
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Old 27 Feb 2007
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Are the airheads with bigger engines more prone to this problem? ie higher torques probably mean greater lateral pressures on the bearing? My R65 monoshock had a gearbox overhaul at 120,000 km (as a precaution), and i did it again at 230,000 km (again, as a precaution). There is no circlip on the output shaft, but i have never had a problem with the gearbox.
sean
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