something amiss here

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something amiss here

Postby Unity » Wed Jul 31, 2013 10:12 pm

Everything else in this picture is pretty much plumb.
Image

There was suddenly a bunch of smoke; Jody said it smelled hot. The first thing we saw was black stuff piled on the driveshaft housing (blue arrow). Then we saw the groove in the sidewall of the tire (red arrow). The wheel is freely suspended in the picture. If it were carrying a little over half the weight of the bike and rider and rider's stuff, the groove would be right beside the charcoal canister. The radii of the groove and the canister appear to be about the same. Hmm.
Image

On the right is the stub of one of the two pivot pins that keep the rear wheel fork and the rear axle housing together. Next to it is an example of one that would go on the other side of the housing (not from this bike). From the bevel up the two pivot pins should look alike (instead of "there" and "missing").
Image

This parts diagram is looking toward the rear of the bike. The broken pivot pin above is #7 on the diagram.
Image

The tail of the rear wheel fork encloses the forward part of the rear axle drive and the pivot pins fasten them together.
Image

Why would a sturdy piece like that -- one that doesn't get a lot of stress -- break that way? George asked if I had hit a big pothole; no, nothing that stands out in memory. George drove one of the bushings out of the rear axle housing. "Did you buy this bike used?" he asked. "Yes, with about 1,000 miles on it; it had a defective clutch plate and the first owner traded it for an LT instead of waiting for it to be fixed," I replied. Then George explained that my RT originally had needle bearings carrying the pivot pins, but the aftermarket was promoting bushings instead of bearings. I guessed they must have been switched -- upgraded -- at the same time the clutch was rebuilt.

The needle bearings (#2 on the second parts diagram) are basically non-maintenance items (snug them to torque occasionally) but the bushings need to be greased. Because they are non-standard, bushings requiring grease are not on the service schedule. George is confident, if needle bearings had been in there as they should have been (and as they are now), nothing would have gone wrong. This is the first instance he has seen of this kind of failure.

--John
(I was doing 70+ mph when the great gout of smoke billowed out. If that sidewall had worn a little bit deeper ... :shock: )
Last edited by Unity on Thu Aug 01, 2013 10:56 am, edited 2 times in total.
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Re: something amiss here

Postby biometrics » Thu Aug 01, 2013 9:01 am

Parts can be replaced and things can be fixed... just glad you are okay!
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Re: something amiss here

Postby Chiba » Thu Aug 01, 2013 4:39 pm

Wow, what a weird thing to go wrong!!
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Re: something amiss here

Postby BKling » Thu Aug 01, 2013 5:15 pm

Wow, glad you are unscathed, that failure could have been a disaster.
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Re: something amiss here

Postby Maria V » Sat Aug 03, 2013 5:26 pm

What Bryant said. Damn.
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Re: something amiss here

Postby endobobdds » Sat Aug 03, 2013 7:33 pm

Thank you for posting and your detailed write up. This is scary and speaks to sticking with original BMW parts in most cases.
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