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#11
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bottom bracket advice
"Ben Fitzgerald" wrote:
I suspect you may be right. The right hand peddle crank does sit well clear of the frame now, which may well be because the axle has migrated to the right. I will try this and let you know. The axle can't migrate within the cartridge. Whichever side of the unit contains the bearings and axle (the left side in the case of your old model, probably the right in the case of the replacement) should be tight in the frame with its flange firmly against the face of the bottom bracket shell. The other side, just a supporting ring, should then be snugged up to support the cartridge from the other side. If you've replaced the original unit with a longer-axled model that fits from the right, you can't adjust it leftward. If the crank is too far from the centre line of the frame, the axle is too long. James Thomson |
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#12
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bottom bracket advice
"Ben Fitzgerald" wrote in message in... On Thu, 8 Dec 2005 01:36:38 -0000, michael adams wrote: "Ben Fitzgerald" wrote in message in... Hi, My bottom bracket is knackared. The axle on the side of the front sprocket (left side) seems to have shortened ... Bottom bracket axles can't shorten. What's hapened presumably is that the bottom bracket cartridge has rotated on the threads inside the shell and moved across. If the above is total nonsense, then presumably it will be corrected in short order. If it's correct then nothing necessarily needs replacement. Only adjustment. Unless the contact with the derailler wire has caused serious damage to the chainring.( front sprocket) Which can be replaced on its own in any case. Just remove the cranks, and loosen the lockring on the bottom bracket cartridge and then thread it through so the correct amount of axle is showing on the chainring side - just try a loose fit to check maybe and then tighten the lockring. I suspect you may be right. The right hand peddle crank does sit well clear of the frame now, which may well be because the axle has migrated to the right. I will try this and let you know. Thanks! Having looked at the diagram helpfully provided by James Thomson - http://bernd.sluka.de/Fahrrad/Shiman...-CT90_1995.gif ( it was guesswork on my part up until that point ) what appears to have happened with the original cartridge, is simply that the left-hand, non-drive side started working loose. i.e unscrewing itself. Bringing the cartridge, and enclosed axle with it. On a traditional cup and bearing bottom bracket, any such looseness on either side would immediately show up as play in the axle. However with cartridges one side fits in a sleeve inside the bottom bracket. And it's the sleeve, rather than the actual cartridge that threads into the bottom bracket shell. And so what happened, is that the whole cartridge including the axle simply slowly unscrewed itself and moved to the left. So all you need do is replace the original cartridge and make sure the left hand side is screwed on tight. ( I won't confuse things or chance my arm with any further with reference to torque wrenches, thread direction, or lock-rings etc.) michael adams .... Ben. -- Registered Linux user number 339435 |
#13
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bottom bracket advice
michael adams wrote: [snip] Fair enough. So how is it possible to account for the fact that the bottom bracket axle has "shortened" ? Has it really shortened as the O.P claims ? Otherwise how is it possible to account for the fact that it presumably functioned o.k up until recently - the front chainrings were correctly aligned - and now they're not? Just asking. The most likely cause is that the BB bearings were sufficiently goosed that they allowed the BB spindle to rock backwards & forwards. At the edge of the chainring, this backwards & forwards motion is rotated to give a side to side motion, allowing the chain ring to hit the rear stay under the appropriate load. The Luggage |
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