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Old 2018-08-04, 04:27 AM   #1
Scoox
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Best way to prevent bolts coming loose?

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):

Quote:
The lockwasher serves as a spring while the bolt is being tightened. However, the washer is normally flat by the time the bolt is fully torqued. At this time it is equivalent to a solid flat washer, and its locking ability is nonexistent. In summary, a lockwasher of this type is useless for locking.
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):

Quote:
Although this washer does provide some locking action, it damages the mating surfaces. These scratches can cause crack formation in highly stressed fasteners, in mating parts, or both, as well as increased corrosion susceptibility.
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
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Old 2018-08-04, 04:59 AM   #2
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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)
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Old 2018-08-04, 08:08 AM   #3
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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.
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Old 2018-08-04, 09:04 AM   #4
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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.
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Old 2018-08-04, 02:24 PM   #5
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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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Old 2018-08-04, 05:39 PM   #6
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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.
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Old 2018-08-05, 02:50 AM   #7
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Quote:
Originally Posted by JimT View Post
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.

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?
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Old 2018-08-05, 03:14 AM   #8
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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.
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Old 2018-08-05, 04:35 AM   #9
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Quote:
Originally Posted by song View Post
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.
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.
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Old 2018-08-05, 07:25 AM   #10
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*That was supposed to read: "I don't think there's anything UDC..."
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Old 2018-08-05, 02:56 PM   #11
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Quote:
Originally Posted by Scoox View Post
......BTW what's that plate with the cable ties for?
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

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Old 2018-08-05, 07:10 PM   #12
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Quote:
Originally Posted by Scoox View Post
Hi, I'm looking for ways to prevent my uni bolts from rattling loose
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.
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Old 2018-08-05, 10:23 PM   #13
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Those bolts on both my nimbus 26 and 36 came with loctite on them and never came loose.
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Old 2018-08-06, 03:13 AM   #14
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Quote:
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Those bolts on both my nimbus 26 and 36 came with loctite on them and never came loose.
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.
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Old 2018-08-06, 03:25 AM   #15
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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.
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