rattling nuts...

[quixoticgeek]

I have a woho anti-sway[1] bottle rack thingy attached to the underside of my saddle. I fitted it originally following the instructions, after a couple of hundred km, one of the bottle cages jettisoned at speed, trashing the SIS bottle in the cage. Fortunately I found all the screws, and bits, but it made me doubt the integrity of the device as was, so I took the other cage off at the road side. A bit further down the road, the whole anti-sway rack came off, and I lost the screws.

Back at home I refitted the cages, this time with a load of blue loctite, and cable tie reinforcement. Where the rack attaches to the saddle, I added nyloc nuts to the bolts as added belt and braces. This lasted a good 2300km. But last week one of the bottle cages came off. The bolts had rattled loose again, as had the screws holding the rack to the saddle. tho the nyloc nuts are holding it in place a bit, but it's kinda lose.

All this brings me to the question, what on earth can I do to stop these bloody screws rattling lose? This rack has cost me 2 SIS bottles already. It's really useful, but if I can't trust it, I'm gonna have to find a better solution.

Thanks

J

[1] http://woho.bigcartel.com/product/pre-oeder-xtouring-2018-standard-percal-service

[Brucey]

I think you did the right thing using longer screws and nylock nuts.   Where the bottle cages mount if there is room to, use a longer bolt and a nylock nut on the back of the fitting (you may need to wrap with tape to prevent the bag from being chafed).  Here and where the thing clamps to the saddle rails, I suspect that it might be a good idea to use some Belleville washers under the bolt head and nylock nuts on the back of the fitting. The belleville washers (which are known as 'disc springs' in the US) provide a joint clamping load that is (to an extent) independent of 'how tight the bolt is' and a stiffness that can be better matched to the bracket that is being clamped.  The bracket stiffness is high where the bottle cages mount and low where the bracket mounts onto the saddle.



 You may not be able to get enough force with a single washer, in which case two or more may be 'nested' to make a spring that is twice as stiff, or 'inverted' so as to make a spring of reduced stiffness and more travel.



If you are going to use loctite on a bracket like that, it is better to use a higher strength grade (e.g. red) than 'blue'.

It seems to me that it is likely that the bracket flexes where it clamps to the saddle, and may deform in such a way as the clamp is going to loosen. With Belleville washers fitted, the peak load seen in the bracket (as, say, you go over a bump) may be reduced enough that the bracket doesn't deform permanently.

cheers

[hubner]

I would use 2 normal nuts locked against each other using 2 spanners. And check and retighten regularly.

I don't see how nylon can give much grip compared with steel.

Yes the thin saddle rails brackets are prob bending and that would loosen the nuts

[Brucey]

using a nylock nut as one half of a locknut arrangement is always a 'win'; it doesn't inhibit you from swinging like a chimp when you tighten the locknuts, but should the whole lot ever come loose, the nylock won't so easily rattle about, spin off and be lost.

cheers

[hubner]

Oh I see, the nylon doesn't actually prevent loosening, it just stops a loose nut from falling off.

[Brucey]

pretty much, yes.  There are a few (mostly very low torque) applications (*) where the nylock action is meant to keep a fastener set correctly all the time, but the main benefit of using them is mostly that they don't spin off and get lost if the fastener ever loses tension. For example nutted brakes have nylocks on them and AK brakes have factory threadlock on the fittings; both are intended to achieve the same thing more or less.

(*) For example on cheap DP brakes, the offset arm often pivots on a bolt that is held captive by a nylock only (no second threaded nut of any kind, just a plain hole through the static part of the brake). Amazingly this seems to work OK (ish); I think they get away with this because the movement is small (when there is load) and if the bolt were to be dragged round, it would only tighten itself.

cheers