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Torque specs on an Urban Arrow adjustable dropout

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Torque specs on an Urban Arrow adjustable dropout

Old 01-28-22, 05:25 AM
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Frkl
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Torque specs on an Urban Arrow adjustable dropout

Hello,

We've got an Urban Arrow and the adjustable dropout assemblies continually slip, creating insane chain tension that is going to put major wear on the motor. I am wondering a) does anyone else also have this problem and how you fixed it, and b) if anyone knows torque that Urban Arrow specs for these bolts?

These specs seem to be a closely guarded secret and our shop just wants me to bring it in (next appointment in March!). The manual for the previous version of the Urban Arrow (without adjustable dropout assemblies) published torque specs for every single bolt on the bike, but there is no such info available for the new version.* More details on the problem and why I think it's happening below.

Here's a picture of the assembly:



The blue arrow is pointing to the M8 stainless pivot bolt, and the red arrows point to the two M6 stainless bolts that (should) keep the assembly from rotating. There is a grub screw that "helps" adjustment. I think what is going on is that, because the pivot bolt is above the axle, tire impacts knock the assembly rearward over time, tightening the chain and stressing the motor. The grub screw is also set up in such a way that it prevents forward rotation but not rearward rotation. The two red bolts thread into captive nuts that can slide in arc-shaped tracks when loosened.

The shop set them too loose to begin with, which caused the original problem, so I don't have a reference value. But I am not sure they can safely be tightened enough in the first place: the fixing bolts are only M6 A2-stainless steel bolts, which have a max torque norm of about 9 Nm. I experimented with this and it wasn't enough. I have carefully tightened them to 15 Nm. If 15Nm isn't enough, my next move will be to get Grade 12.9 bolts rated to 20 Nm.

Thanks so much!

*I think Urban Arrow is trying to discourage people from doing their own maintenance on the bike; they will even void your warranty if you don't do yearly maintenance at an approved dealer! Suddenly, owning a cargo bike feels a lot like owning a car...

Last edited by Frkl; 01-28-22 at 01:32 PM.
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Old 02-09-22, 02:27 AM
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Frkl
Must be symmetrical
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Reposted in Bike Mechanics, please reply to that thead, not here. Thanks

https://www.bikeforums.net/bicycle-m...e-dropout.html
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