Dear Mister Loctite

Hi Folks!

This one is just to give thanks to Mr. Robert Loctite (or whatever his firstname is :slight_smile: ).

I’m the happy owner of a N36, but still I’ve been damaging cranks and cranks over the last 2 years, and shouting every day at those crappy square tapered axles/cranks. The cranks were systematically getting loose after some time - yet I tried quite a few different models, in aluminium, steel, of different brands, etc.

This - until I decided, on last week-end, to (at last) make use of the Red Loctite tube I had bought from UDC quite a long time ago - without having since then taken the decision to “do it”.

Well… even though I read from RSU archives that the Blue one seems to be strong enough and that the Red Loctite was perhaps too strong for my purpose, at least I can testify after a few days of use that my problems are (fingers crossed) gone!

I would therefore really recommend this Loctite trick to those of you who are desperate at owning square tapered axles/cranks.

Cheers, MadC.

PS: this being said, I am still dreaming about an ISIS-compatible wide hub to equip my 36er - NO DOUBT! May the new N36 from UDC be ISIS-based… :roll_eyes:

There’s more to solving this problem than locking your bolts…

I’ve found that aluminum square taper cranks will fail when large torques are applied, either slowly or catastrophically. Hence, I will only recommend using steel cranks on square taper hubs.

I’ve also found that, unless one has access to an arbor press, installing square taper cranks isn’t as simple as tightening a bolt… it’s more of a process. The crank and axle must first be cleaned, then lubricated. The bolt must also be lubricated. Once tightened, the bolt must be re-tightened after every ride for some time until the crank “finds its seat” and stays put.

If you only tighten your crank bolt once, you’re running with a crank that may not be fully seated. That increases the risk of damaging the crank, ultimately leading to premature failure… and that’s never fun when you’re 10 miles from the nearest trailhead.

Just my two cents.

In short, Loc-tite works great for a short-term fix, but unless you install that crank correctly on your first try, you may be in for trouble in the long term.

which loctite did you use? as far as i know loctite sell atleast 100 different products which are red, usually there’s a large number on the front of the pack i.e loctite 272

That would be, “Thanks, Vern!” From :

“More than 50 years ago, Loctite® brand adhesives were developed in a Connecticut basement laboratory by Dr. Vernon Krieble.”

That’s actually the 262.

Cheers, MadC.

Sure - I can definitely confirm this.

Oh, really? I’ll do as if I had not read this one… :slight_smile:

Very interesting… I may have underestimated this process from the beginning - not that I was doing it in a neglecting way, but for sure not as carefully as what you are describing.

Cheers, MadC.

I don’t know why people get so much trouble with square-taper cranks coming loose. I’ve only ever had two instances of cotterless cycle cranks coming loose in my life (which is a lot of riding, believe me) - once on my coker, with steel cranks, and once on the only splined set I’ve ever owned (on my winter commuting bike). Never had one problem with aluminium square-taper cranks on any cycle (bike or uni).

I’m not a huge jumper or dropper and my xc riding style is to roll everything, but even so my muni cranks get a considerable amount of vibration on the rocky trails round here and are often dropped hard on rocks. I’ve had cracks developing in my muni cranks (prowheel 152s) but never any problem with the crank/hub interface.

Am I just incredibly lucky, or unusually careful installing cranks (quick wipe clean, grease tapers, dab of mild thread-lock on the bolt, do up to 35lbf, never touch again for years), or not cool enough to break stuff (although I think the original poster was referring to road riding, not extreme muni or even xc)?


The problem with the square taper design is that there is no stop on the hub/spindle to keep the cranks from sliding further up the taper when you pedal really hard. When you pedal really hard (or land a drop) the cranks will want to take some of that force and slide further up the taper. When you relax your pedaling the cranks will slide back down the taper. When the crank slides up the taper it reduces force on the bolt or nut that is holding the crank from falling off the tapers. If that force is reduced enough the bolt/nut can loosen by a fraction of a degree. Then the crank slides back down and the bolt/nut is tight again. That cyclic process means that the bolt/nut that holds the crank on can eventually become loose enough for the crank to fall off or the crank to become wobbly.

Medium strength Locktite (or generic threadlocker) on the threads of the bolt or nut is enough to keep it from loosening on its own. If that bolt or nut stays tight, and the cranks were properly installed, and the taper on the cranks is not worn, the square taper setup can be reasonably reliable.

There is no need to Loctite the taper itself. A little bit of grease will do fine there. The Loctite is just needed on the threads of the bolt or nut.

Dave Stockton wrote up a procedure for installing square taper cranks. Follow that guide and your square taper problems on a Coker or other unicycle will be mostly solved.

It is also important to use good cranks. Some cranks just have a wrong taper that doesn’t properly match the taper on the hub. Other cranks are too soft and that allows the crank to move farther up the taper during hard pedaling and are more of a problem. Some steel cranks have a bad taper.

I’ve been using Kooka cranks on my Coker and have never had a problem with a loose crank and I never expect to have a problem. They’re the custom Kooka cranks with three pedal holes (130, 150, 170). I installed the cranks with Loctite when I first got them and haven’t touched the retaining bolts since. When I want to change crank length I change the pedal position rather than changing cranks. I haven’t touched or checked the tightness of the retaining bolts since installing the cranks (checking the tightness would break the Locktite bond and require that I re-Loctite the bolt and if the Loctite is holding there is no need to even bother). The steel square taper cranks I have on my freestyle unicycle have also never come loose. They’ve been on the unicycle for several years without me ever checking the tightness of the retaining nuts (checking the tightness would break the Loctite bond).

ISIS Drive would be preferable to the square taper. An ISIS wide Coker hub would be nice especially now that there are suitable range of lengths and styles of ISIS unicycle cranks available. With ISIS you can forget about pretty much all of what I wrote above about square taper cranks.

I had my pedal on my 24" Torker come loose and ruin the threading on my cranks. I’m now on my wife’s 20" until I fix it. I’m a new rider, so I’m just getting initiated on the equipment and whatnot. I did however put some loctite on my wifes 20" and haven’t had any problems so far… I will prob use loctite for insurance from now on, it’s gotta be cheaper and easier than replacing crank arms and pedals.

To reiterate…

Loctite alone won’t ensure your crank arms stay put… they’ll only hold the crank bolt in place.

If you didn’t install the crank arms solidy to begin with, then no amount of Loctite will keep the crank arms in place.

Thanks for the insight onto ‘why’ !!!

I’m not convinced at all by that explanation. Why would the crank try to force itself further onto the taper when under load? If anything I’d expect it to be pushed off the taper as it twists (i.e. against the bolt, not away from it). It can’t move because the bolt is there. I agree that multiple shocks do eventually loosen the bolt, which is why threadlock helps. The continuous flexing of the crank-axle interface eventually wears the inside of the crank (which is always softer than the axle) and it will start to become loose, by which time it’s usually too late so save them even if done up again (when it will indeed go further up the taper). Doing the crank bolt up very tightly in the first place stops the crank from squirming and prolongs the life (as long as the crank isn’t such poor quality that it cracks when you do it up, like Maestro suggested - prowheel cranks are pretty meaty round the axle end and I’ve never had a problem with one cracking when done up tight [although I have had cracks in the middle of a prowheel crank]).

As for the comment that square taper cranks are bad because they don’t have an end stop to tighten against, I disagree with that as well. When you do up a square taper crank it goes up the taper until it is a tight fit against the axle faces. After a number of removals and refittings, it will go a bit further up the taper due to slight wear and distortion and will eventually reach a point when it touches the bearing holders or the bolt bottoms out, when the crank is scrap. But at least up until that point (which can be a very long time if you don’t remove your cranks often) they fit perfectly.

Splined axles with an end stop assume everything is perfect. There is nothing to take up any manufacturing tolerances or slight wear, so it’s pretty much always slightly loose even when new and works the bolt free as it moves. The splined setup on my winter commuting bike is really quite nasty (it’s not ISIS I don’t think - some sort of proprietary Truvativ BB) and needs the bolt really firmly locktited up to stop it coming loose every few hundred miles. Presumably ISIS is a bit better, being a tapered design - and presumably doesn’t use end stops (but I haven’t really looked at an ISIS axle so I may be talking bollocks).

I have honestly never had a problem with aluminium square taper cranks coming loose on bikes (including xc mountain bikes when I used to ride them) or unicycles. The only problem cranks for me have been steel ones on my coker and the Truvativ splined set I mentioned.


It’s the explanation that Jobst Brandt came to after studying the issue. I’ve read several articles and old newsgroup posts about what he had to say about square taper cranks and his explanation makes the most sense from an engineering standpoint. Here’s one of his articles on the subject: Installing Cranks. There are others that you can find with web and newsgroup searches.

Metal can have elastic deformation. Aluminum cranks moreso than steel cranks. The elastic deformation would allow the cranks to slide up the taper and then slide back down while still being snug and tight. Because there is no stop on the taper to prevent the cranks from sliding further up the taper the cranks are free to elastically deform and slide up the taper then relax and slide back down.

OK :confused:

It still makes no sense to me that the crank would try to slide further onto the taper when it stretches (I know about elasticity - I’m not an idiot). I could imagine it stretching (OK, elastically deforming if you like) and moving slightly over the corners of the square taper, but forcing itself further onto the taper just sounds ridiculous.

But I see no point in arguing - the point is that fit cranks properly and do them up tightly and they don’t just fall off.


Too late to edit…

I read the Jobst Brant article John linked to and he(?) does indeed suggest that the crank will “elbow itself away from the bolt and up the taper as it sqirms around” (not an exact quote but those are the words he uses). Very weird.


It is weird. The force components are not intuitive or obvious. Mix in the effects of torque (right-hand rule), precession, and other factors and you can end up with force components going in directions that you don’t expect.

Maybe Harper can explain why?

Must admit that i tend to agree with Rob, but as i respect your opinion I’m prepared to be open minded. As I’ve just got my hands on CAD/FEA software I thought I might knock up a model to see what happens, does anyone know dimensions of a standard square taper, particularly the angle of the taper?

I trust Jobst Brandt to have done the analysis correctly and come to the correct conclusion. The details as to how and why it gets the force to move up the taper is beyond my engineering knowledge.