Hi All,
Not an e-bike specific question but I hope you can help... I have a Dahon 7 Speed with a 3 piece bottom bracket hub. This is becoming loose, I tighten it and then after a ride it is loose again (shaft moving up/down).
So, either the bearing/cage are faulty and/or I'm not tightening the lock nut tight enough? just how tight does the lock nut have to be please?
Thanks,
Brian
When you say "3 piece bottom bracket hub" do you mean an axle and 2 threaded cups (Ball races) that screw into the bottom bracket shell?
Getting the torque right on the lock nut is important but so is the torque on the fixed cup (right hand side). That has a no lock nut but is screwed into the bottom bracket shell as tight as you can. The motion of the axle when riding can unscrew it if it is not really tight.
The left hand cup, has the lock ring on it. It should only be done up tight enough to allow free revolving movement on the axle WITHOUT ANY END FLOAT OR SIDE TO SIDE PLAY.
The lock ring should be done up as tight a sensibly possible: since this tends to pull the adjustable cup out a little (a thou or two): trial and error is required.
Having the right spanners (wrenches) greatly facilitates this exercise since they need to be a fairly precise fit to get the right purchase. Perseverance in getting the free movement of the axle right is also useful.
When you have made the adjustment turn the axle a few revolutions and check again for end float and side-to-side movement.
If after another run you find slackness or movement in the axle, check the right hand cup first to make sure it has not worked loose.
You may have a broken ball bearing in the race(s) or a ball missing. This would contribute to the inability to keep the remaining balls in their place.
On the other hand, it may be that the races are worn. Even more "bad news" is that the threads in the B.B. Shell have become damaged or worn and will not keep the cups where they should be.
All is not lost: just buy a Bottom Bracket Cartridge with the right axle length. Make sure it has the right threads (some are left hand/right hand). I doubt if the threads are French or Italian, but that's no problem if they are - just get the right foreign Cartridge: they are all available in the UK (though I doubt that the perfidious English threads are freely available on the continent).
A phone call to Dahon (or AtoB) will tell you what you've got.
Good luck!
Peter
P.S. Check that the "faces" of the B.B. Shell (where the races are screwed in) are square to the B.B.Shell. If they are not, everytime you tighten the lock nut the adjustable cup will be pulled out enough to create slack in the axle.
