Hello everyone.
On unicycles (aluminum forks) that have a thread in the bearing shell, the Allen screws can suddenly come loose if they aren’t secured or pre-tensioned. This is particularly annoying if you don’t have any tools with you.
I’m testing my new Fatty forks for the long-term and I’m not sure which solution would be better:
- Use a spring washer to prevent the screw from suddenly coming loose.
or
- Use a locking screw (Nylok) and a regular washer instead.
The spring washer version is available at any hardware store and is therefore easy to obtain.
What are your experiences? Which holds better?
I’m currently using a spring washer, and it seems to be holding up well.
I‘m using Loctite (the product type, not the brand). Works quite well for me. Has to be re-applied maybe every third time I‘m loosening/tightening the screws.
Nyloc should work well, but means additional hassle to deal with, when used in frames with a threaded bearing seat.
Spring washers could work, too, but I have some concerns. They‘re usually used when the bolt is tightened firmly. But we usually don’t do that in order not to squeeze the bearing. If the tension of the washer is stronger than that resulting from the bolt tightening you end up with a spongy assembly.
My idea with the spring washers is to keep the screw under tension so that there is no breakaway torque (sorry, that’s probably not the technical term). Of course, you have to keep an eye on it so that you don’t overtighten or undertighten. I think there are different strengths of spring washers. I also think that the spring would press against the screw if it were to turn anti-clockwise. So it would create additional resistance. But that would mean only fitting the screw and spring washer, without a washer like you normally do. Anyone can put Loctite on it, of course. But that doesn’t work in series production. That would probably be these Nylok screws.
I’d recommend against using a spring washer for anything. When springs are compressed in series, the properties of the stiffest spring dominate, and in a bolted joint, the tensioned bolt behaves like a stiff spring.
In practice, by the time the bolt is unscrewed enough transfer any strain to the washer, it’s already too loose. I’ve linked an article about this below, but you can also test this for yourself by loosening a bolt until the spring washer starts to decompress. Judge the torque required to turn the bolt, and the play in the joint, and I think you’ll come to the same conclusion.
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Thank you very much, this is a very interesting article! If I understand correctly, there are actually only disadvantages. I’m still doing my own tests, though. Funnily enough, it seems to be better for me with the spring washer than without. But maybe I’m just imagining it.
There’s also Nordlock, but they are pretty expensive. And I’m not sure they would really work given the low tightening force of the given application. But compared to simple spring washers they are way harder to unscrew - if tightened firmly.
There’s a hack to keep the bearings running smoothly, with minimal wear, and tighten the screws (then they won’t come loose as easily): Clamp enough washers on each side of the bearing shell to exactly close the air gap. This creates the effect of a sealed bearing shell. However, it’s tricky to get just the right thickness. In the past, there were some unicycles with sealed bearing shells, such as Imholz or Pichler. Anyone who has ridden them can confirm that they rolled very well.
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Yeah, I‘m pondering for a long time whether to go that route or not. It‘s just a hassle to find the correct thickness, as you pointed out. Plus, at least the frame I did play with doesn‘t feature perfectly parallel bearing seats and shells. This means I should scrape them first, but I‘m too lazy and even if I wasn‘t, I don‘t have the time right now.
yes it only works if the screws of the bearing shells have enough distance
I think it’s typically an either or situation. If you had both threads and a nut, you actually would not need nyloc, you could tension them against each other, which solves the whole bolt coming loose issue.
Maybe not pretty enough as a commercial product, but mechanically actually a neat solution.
You can of course also solve this by using a 5mm longer screw and putting the nut on the other end of the bearing shell. At least that works fine with the forks I’ve tested. It just doesn’t look good. For me the normal solution with a spring washer actually holds up pretty well. Of course you should check these screws before a longer tour and tighten them if necessary. Since I never go on a tour without my folding tool it’s not a problem anyway. With nylok I’m bothered by the tightening torque. You somehow have no control over whether the resistance is coming from the screw or whether you’re already squashing the bearings.
I thought that was your initial intention, but I obviously got this wrong.
I tighten the shells until the bearing I‘m working on starts to slow the wheel down. Then unscrew until the wheel turns freely again.
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