loose crank...solution?

My left crank is loose and I have to carry a socket wrench with me as I ride.

I’m sure I am not the first one to experience this, so I am asking what you more experienced unicyclists would do in a case like this.

I think putting blue loctite on the threads is what I heard.

Much simpler: fit it properly.

Whatever you do, don’t ride with it loose. You’d damage your hub.

Remove the crank. If it works really loose, you might be able to do this by hand, or it can be achieved with a suitable combination of blocks of wood and a mallet.

BUT, as with every job, the best way to do it is with the proper toll, which is handily designed for the job. A crank remover tool is an essential part of my tool kit.

Remove the crank. Clean the mating surfaces on the inside of the crank, and the tapers of the hub. Put the crank on neatly, then tap it into place with a rubber or wooden mallet (or a big block of wood and a hammer). A couple of sharp taps will do more good than lots of tappity taps.

The idea isn’t to force it on really hard, but to make sure it is properly seated.

Now tighten the nut or bolt (varies depending on what type of hub you have) with the 14 mm socket.

Rid for a few hundred metres, then get off and tighten it again. Check it again a few hundred metres later, and then it should be OK.

Every ride, just check it hasn’t started to come loose - especially if you ride hard, do big drops or fall off a lot.

Re: loose crank…solution?

On Tue, 26 Jul 2005 14:36:22 -0500, “Mikefule” wrote:

>Put the crank on neatly, then tap it into
>place with a rubber or wooden mallet (or a big block of wood and a
>hammer). A couple of sharp taps will do more good than lots of tappity

Dangerous advice!

I destroyed a set of cranks (Bicycle Euro, steel) by repeatedly
hammering them in place with a metal hammer, with a thick wooden block
in between. The damage isn’t immediately obvious but you develop tiny
hair cracks in the corners of the square hole in the crank, and they
irreversibly grow during riding/jumping/etc (due to stress
concentration) to such an extent that your cranks work loose all the
time. The only remedy is new cranks.

There is a complete (and proper) description for the correct crank
installing procedure if you SEARCH for it. John Child and Harper have
posted it repeatedly. It involves only gentle tapping on the crank,
and only so much that the nut engages. Then let the nut to the rest.
(Or use a press but not many people have one at their disposal.)

Klaas Bil - Newsgroup Addict

I ride like a princess. - john_childs

I do the same as Mike Fule, but with the addition of putting vasaline on the axle prior to putting on the crank. This, in theory, enables the crank to become seated better on the axle. I do use a hammer and wooden blocks, but take care not to hit it too hard or too many times.

Prior to using this method, my cranks used to come loose; since using it, they don’t. Although I always carry a crank nut spanner on rides just in case, i think I’ve only needed to use it once in several years of riding.

U-Turn has a good writeup for crank installation on his web site: LiveWire Unicycles: Square Taper Crank Installation and Maintenance

Note that there is no need to pound the cranks on. The grease and the torque wrench will allow the crank to get properly tight with no pounding needed.

My procedure is slightly different than described but close enough that it doesn’t make a difference.
Two keys:

  1. Use a torque wrench
  2. Use Loctite threadlocker

I use Red high strength (permanent strength) Loctite threadlocker. It’s trivial to break the bond by hand with a regular 6" socket wrench. But Blue medium strength threadlocker is plenty strong enough. Use what you’ve got on hand.

There is no need to check the tightness before each ride if you use this procedure. In fact, pulling out a socket wrench and tightening up the nut just to be sure they’re still tight will break the Loctite threadloker bond and negate usefulness of the Loctite. Just leave it be. They should stay tight. That’s what the Loctite is for.

If your cranks come loose fairly quickly after using this procedure then the taper on either the hub or the cranks is likely damaged and the cranks are never going to stay tight.

A torque wrench isn’t necessarily expensive. I found a Craftsman torque wrench for under $25 (see the thread I’m Torqued). You can also find inexpensive torque wrenches at places like Harbor Freight. The torque wrench eliminates the guess work and really is important. It’s the quality control to make sure your cranks will stay tight. Otherwise it’s all guess work.

Re: Re: loose crank…solution?

All advice is dangerous because it relies on the advised interpreting it properly.

I have changed my cranks more often than most and so far have never damaged one. A sharp clean tap with a mallet rather than a series of tappity taps or massive thumps is perfectly OK. The idea isn’t to hammer the crank onto the taper, but to make sure it is properly bedded. It’s a question of degree and common sense.

That said, I don’t usually bother with the mallet these days, and they don’t usually come loose. As with any job, the answer is to do it carefully and cleanly.

As for Loctite - so far, I have gone through a whole life of bicycling, unicycling, motorcycle maintenance and fencing club armoury without relying on this stuff, yet everyone recommends it.