Best way to prevent bolts coming loose?

Unicycles and Equipment
1

Hi, I’m looking for ways to prevent my uni bolts from rattling loose, specifically the bearing housing bolts of my KH uni. I would like my uni to be as maintenance free as possible, always good to go. How do you guys get your bolts to stay put?

I have a bottle of Loctite 242 threadlocker but it’s either counterfeit (I live in China) or it simply doesn’t work well. I apply it and it never seems to fully dry, and it always makes a mess. Threads are still sticky even days after application. Maybe I’m using too much (one or two drops usually). Then there’s the newer and better Loctite 243 (blue) which I haven’t tried, and Loctite 248 threadlocker stick.

My problem with Loctite is that it has a 24-hour minimum curing period, so if you need to take off your wheel to repair a puncture and continue riding, I assume threadlocker is not going to do much good. On the other hand, threadlocker residue from the previous application adds a bit of bulk and increases friction, but I imagine it won’t stop the bolts from eventually coming loose.

My Teliang 19" uni uses Nyloc nuts, while my KH27.5 has threaded housings and split washers (technically termed “helical spring washer”). Based on personal experience with my KH27.5 uni, split washers don’t work. Here’s what NASA say about lockwashers (Source: NASA, 1990, Fastener Design Manual, p. 13):

Then there’s also this interesting video:

Nord-Lock Wedge-Locking Washers - Junker Vibration Test - YouTube

Despite the findings of the video below, the Nylock nuts on my 19er appear to be doing their job. I think effectiveness depends on the intensity of the vibrations. Split washers apply a small amount of preload which may be a good thing because unicycle bearing housing bolts don’t need to be too tight.

Next thing I’m going to try is plumbers PTFE thread seal tape, will it work? Probably not, but it’s worth a try.a

I could buy longer bolts and put Nyloc on the end in addition to the existing frame threads, which would give me a combination of the two most effective friction-based locking methods—Nylock nut and double-nut (as per above video). Maybe I could keep the split washers with a regular M6 washer to protect the frame from carnage (again, from p. 13 of NASA’s manual):

Nord-Lock seem ideal, but I have a feeling the torque required for the washers to bite into the bolt is far greater than the torque required by unicycle bearing housing bolts.

Anyway, ramble ends here, I’d know to hear how you do it.

PS Is there a way to insert a Youtube video in forum posts? Thanks

2

Here’s the link to NASA’s document in case anyone is interested, personally I think this document is pure gold:

NASA Fastener Design Manual (PDF)

3

I have 3 KH unis: 24, 29 and 36, and I have owned various cheaper unis. I have never used any form of thread locking compound and I have never had a problem with them coming loose.

4

The KH should have spring washers under the head of the bolt:

which should be sufficient to hold the bolts in place. I have several KH and none ever caused a problem. The only bolts coming off slowly being the saddle ones.

The bearing holders should be tightened until the wheel doesn’t spin freely, then you back them off a little until the wheel turns freely.

5

This works for me. The bolts can be torqued tight without putting too much stress on the bearings and the bolts do not work loose.

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6

I seem to remember from years ago someone who couldn’t keep his bolts tight ended up getting long bolts, and backing them up with nylock nuts. So basically you just run the bolt through the bearing cap, and secure like you normally would, but use a nylock as a lock nut for the assembly.

I don’t think I could find it if I tried at this point it was probably 10 years ago! Anyway, it seems to be a sure fire solution to the problem.

7

Did that on my 19er and the assembly has been pretty solid from the start. On the KH the gap between the housings is very tight, I will try 0.1 mm shims, a bit more torque and plumbers tape on the bolt thread. I’m away visiting relatives for the weekend so that will need to wait till Monday.

BTW what’s that plate with the cable ties for?

8

Nord-Lock seems a bit like overkill in this particular case. Nyloc nuts have been fine for me, and my 29 has been OK without them. The bearing cap bolts on my 29 do have some blue Loc-tite on them (can’t remember if it was I who put it on), but I scraped most of it off the last time I took that uni apart.

I have never had a problem with Loc-tite getting runny the way Scoox mentions, but I have very seldom used it. I did put some on the little bolts under the seat that hold the saddle horn in place on my 20, but only because I was doing a lot of hopping at that time.

Scoox, since your 27.5 is new and fancy, you might try contacting UDC again. Maybe they can send you some washers or whatever, or at least offer some advice.

9

I there’s anything UDC can about this other than to recommend threadlocker which they themselves sell. All friction based locking solutions are never going to be as good as proper “positive locking” solutions (e.g. a locking pin going through a notch in the bolt head), but it helps if the better options are employed, e.g. Nyloc.

Re. the bolts on the underside of the saddle, I think it’s kinda silly the way they designed that. All my uni saddles had spring washers there do nothing as far as locking goes and do a good job at messing up the plastic. Not to mention the fact that the inner diameter of the spring washers is about 1.5 mm greater than the bolt thread diameter, so the washer is never concentric with the bolt, if that makes sense. A much simpler solution would have been if the holes in the plastic were deliberately made smaller than the bolt thread diameter, so fro example 4.5 mm for an M5 bolt. This way the plastic of the saddle would itself act as a locking ring similar to Nyloc.

10

*That was supposed to read: “I don’t think there’s anything UDC…”

11

The stainless steel plate holds the speedo sensor. It is more secure and easier to get adjusted correctly then trying to attach the sensor to the fork leg. You can just barely see the black wire coming out the top.
Jim

12

Have you had this problem already, or are you anticipating having the problem and trying to avoid it? All my unicycles are Nimbus. I’ve never had a problem with the bearing cap bolts coming loose. I don’t use washers in the gap like JimT. I can imagine there would be more chance of the bolts coming loose while using washers. Without washers, you tighten the bolts to an arbitrary amount of torque. With the washers, you may be effectively “bottoming out” the bolts. When done correctly, JimT’s solution may be superior, but it seems like there is too much chance of over or under tightening the bearing cap bolts. Generally, when I check the tightness on the bearing caps bolts, they need only a tiny bit of tightening. Maybe between 1/16 and 1/8 of a turn (of a single bolt). Trying to adjust the shims/washers by that much seems pretty tricky.

Most of the time I have to tighten parts of my uni, it’s because the stress and weight I’ve placed on the uni has caused parts to deform slightly. Very rarely have parts come loose from vibration. Applying Loctite doesn’t seem like a good solution for me. Locking in something that is getting loose, to my understanding, will cause damage to the unicycle.

13

Those bolts on both my nimbus 26 and 36 came with loctite on them and never came loose.

14

If you mean a patch of dry blue stuff that comes pre-applied to bolt threads, I don’t think that’s the same as Loctite. That stuff seems to work straightaway, no curing needed—it certainly makes bolts considerably harder to turn when even on the first tightening, unlike Loctite which feels almost like a lubricant and requires 24 hours (minimum) to work its magic. Loctite, being an anaerobic threadlocker (I believe that’s the tech term), cannot be pre-applied.

I think the pre-applied stuff is some sort of sprayed-on nylon patch, something like this, if anyone knows what it is I’d be very interested. Every time I google “threadlocker” I just get Loctite. I hate the stuff. Just because they’ve invested heavily in marketing doesn’t mean it’s the best solution.

15

The blue stuff is likely Nylok® Blue Nylon Torq-Patch® Tuflok®. That looks like what was on my Nimbus bearing cap bolts. It did not work, after a few dozen miles the bolts worked loose.
Jim

16

Yeah! That looks like it. You say it doesn’t work though? Isn’t that the sort of stuff bike parts manufacturers use on their bolts? Now I’m worried :thinking:

17

I’ve had this problem already. I started hearing a clicking sound when mounting and later it started to happen when pedalling. I flpped the uni upside-down and one of the housings was loose enough that I could move it.

The bearings will usually start to deform long before the housing threads yield, and yet tightly tightened bolts are less likely to rattle loose. Without the shims you have to choose between screwing up your bearings or bolts coming loose. Adding shims of the right thickness seems like a good best-of-both-worlds solution. Whether the shims help reduce the chances of loosening is open to debate, but they certainly protect the bearings.

In theory medium strength Loctite (blue) shouldn’t permanently lock the threads, at least that’s what the product spec says.

18

Super neato!

19

A bolt that is in good condition and tightened the correct amount (“correctly torqued”) should stay i place. An exception might be if the bolt was in a component that vibrated at a constant frequency for long periods, which might set up an oscillation that gradually loosens it. Another exception might be if the bolt were holding two components together which rotated in relation to each other. However, in most applications, a bolt done up properly will stay done up.

A bolt is held in place by friction between the male thread and female thread. That is a lot of surface area because the thread winds around the bolt so many times. If the bolt is “nipped up tight” the slight elasticity in the metal will hold those surfaces together more tightly for optimal friction.

It should not be necessary to use additional means on a unicycle. However, if you choose to do so, the two options are (1) something that binds the threads together (some sort of locking compound) (2) something that adds friction to the system (e.g. a nylon insert) or (3) something that adds elasticity to the system (e.g. a nylon washer or spring washer, which is compressed as the bolt tightens, and therefore tries to push back, and increases the force between the male and female threads.

In an ideal word, we would all use torque wrenches and correctly torque up all bolts. A unicycle is basically a simple machine and this might be a bit overkeen for most of us. Tighten the bolt until it stops turning easily, then nip it up an extra quarter turn or so. Don’t over-tighten it or it might go “dink!” and break, which is a real nuisance when it happens.

You can get a good idea how much torque to apply simply by looking at what size spanner or allen key the designer had in mind. Look at a rack of spanners and you will see that as the heads get bigger, the shafts get longer. The same with Allen keys and Torx keys. This means that the bigger the bolt, the longer the lever they expect you to use to tighten the bolt.

In my garage, I have 20, 24, 24, 28, 29, & 36 inch unicycles, 3 bicycles and a motorbike. For decades, I have used this approach, never once used threadlock or any similar product, and never had a problem.

That said, it is common sense to check over your unicycle periodically looking for wear and damage, and there’s an opportunity to double check the bolts when you’re doing so.

20

It is highly useful on bearing caps, since you can’t torque them down without deforming the bearings. It’s a desaster from an engineering point of view.