Loose Crank

A few day’s ago while commuting to school I felt a strange wobble on my left pedal which was accompanied with a sqeaking sound whenever the pedal was weighted. Assuming it was the pedal I posted below - see ‘Pedal Wobble’ - and after receiving John’s suggestions decided to switch to another set of pedals and work on checking over the original pedals on the weekend.

Lo and behold, this morning I set out for the usual ride to work and there it is, more than ever, the squeaking and wobbly feeling on the left side. Almost totally new Wello go B-37 pedals graced my Doteck 140 mm cranks; it couldn’t be the pedal! Sure enough it seems like my crank is loose…:frowning:

So now I am heading to school with the four wheels and motor and going to have to try to tighten the crank tonight.

any ideas? I expect I just have to take off the pedals, sandwich the cranks in wood and ‘whale on the crank’ with a padded hammer like I did when I was first installing them, right?

Would my LBS have a better way of getting the cranks on more securely, I wonder? :thinking:

As always, I appreciate and rely on the advice of the folks on this board.


get a torque wrench and get thoes suckers tight with 40 ft/lbs Darren Bedford recomended this to me and it seemed to work great. Since than I’ve been using this method non stop.

I’m glad I will never have to do this again with my uni though, profiles are on the way :smiley:

Put a little bit of grease on the crank taper before installing the crank. The grease will allow the crank to slide on all the way on the hub and will get the crank seated more securely.

If you’re paranoid or if you’re having problems with the crank nuts getting loose you can use red (high strength) Loctite threadlocker on the retaining nut. This will keep the retaining nut nice and snug.

If you go to a bike shop make sure they use grease on the tapers. Some bike shops might not be willing to use grease on the tapers because they believe that it may damage the taper. Scott Bridgman has an excerpt from one of the bicycling FAQs that disputes that. <http://www.muniac.com/emuni.htm> and scroll down to “Crank Installation”.

If you were riding with a loose crank you may have damaged the taper on the hub or on the crank. Aluminum cranks are more likely to get damaged than steel cranks because the aluminum is softer than steel.

I’ve been using 35 ft-lbs but thinking of moving it up and 40 sounds good. Grease on the spindle; blue (or red) loc-tite on the threads; like John said you’re all set. Best to redo it every couple of weeks or so, or whenever you suspect them. When you redo, you need to remove everything, wipe them down, and refresh the gooey stuff.

The torque wrench runs $90 USD and is worth the piece of mind IMHO.

you need either a torque wrench or just a decent socket, don’t put them on with one of those weeny crank remover / putter onner tools and a little spanner.

Joe R told me that with my nice big socket handle I’m gonna be able to put it on much better than whacking it with a hammer, so basically the whacking the crank bit is pretty useless if you’re using a decent tool to tighten the cranks.


Ok, so the first thing I am going to do is pull off that left crank and see how much damage I did to the crank and/or hub by riding 30+ km’s without knowing that it was the crank that was loosening! :astonished:

Then I’ll decide on one of the following:

  1. if there is damage to the crank - dig out my orginal 127’s and have my LBS install them (so that I am sure they are tight enough)
  2. damage to the hub - think about ordering a new wheel as I don’t think it would be worth the expense to have the orginal Sem XL freestyle wheel rebuilt

that’s the plan for now, what do you think?


Joemarshall wrote:

Search for a post by Phil called "potentially expensive " to see what could happen when installing a crank with the above mentioned method.

I have a related, recurring crank problem, if anyone would care to comment…

My right (only) crank “loosens” every ride – within an hour, it’s creaking and needs retightening. So far, it hasn’t gotten loose enough to feel any wiggle, just the creaking noise. 170 mm Dotek. Here’s what’s different though: the nut does NOT seem to be backing off any; rather, the crank nut needs an additional approx. 1/8 turn – about 2 “clicks” of the nut (each click being one movement of the built-in locknut inner facing). So I’m slowly exposing more and more thread as I keep tightening the nut from ride to ride. I’ve looked for tiny cracks in the crank, but can’t see any. Not sure why it keeps going on deeper and deeper. Do I just keep tightening it, or am I missing something?




If you reuse the Dotek cranks, check their tightness frequently for awhile. If they are slightly deformed you may not see it. The steel taper on the axle will reform the taper in the aluminum crank somewhat, but won’t do it all at once. Put on the cranks and tighten them. Ride half a kilometer and then retighten them. Ride a kilometer and tighten them again. If they are noticeably loose (can be tightened) each time, you are gradually reforming the square taper without rounding it. If you let them get too loose, they will start trying to round out again. After two or three iterations they will no longer tighten.

Look at jerry’s post, above. This is what is happening when the aluminum female taper is being formed by the steel male taper. Initially these two parts don’t fit too well. As the crank is stressed, the aluminum starts to ooze around. Eventually the two surfaces will fit very nicely and you won’t be able to tighten the crank nut anymore. All of the gaps between the crank and axle tapers will be filled. I have done this on Dotek cranks, Lasco cranks, and Shimano cranks, all of them aluminum.

Don’t put grease on your saddle. You’ll slip off the unicycle.

Whether or not you bash on the cranks, the point at which lots of force is put on the thread (assuming you’re sensible and have greased the spindle, so the crank goes on okay) is surely when the nut is being tightened at the end. I don’t see how bashing the crank with a hammer does anything to change that fact? You could overtighten it either way, although my nice socket handle is only 170mm or so, so it seems unlikely.


I’m not advocating “bashing” with a hammer as the only method of crank installation, but a C-clamp or rubber mallet used judiciously (with grease) to assist the crank further down the taper, seems to lessen the load on the threads.
I’m not saying that it can’t be done without a hammer, but I learned the hard way that the threads seem to be the weak link when put up against the harder retaining nut.
I too suffered the same fate as Phil, actually worse, both left and right threads were gone on one of my Suzue hubs. I’m much more careful now. In my case, I was used to years of installing and removing cranks from bicycle bottom brackets with internal threads and retaining bolts rather than the external thread and nut found on unicycles.

Thanks Harper! I too have been experiencing the forever-loosening crank nuts. Now I know why.

Re: Loose Crank

On Wed, 26 Mar 2003 16:58:21 -0600, U-Turn
<U-Turn.kx7qz@timelimit.unicyclist.com> wrote:

>I’ve been using 35 ft-lbs but thinking of moving it up and 40 sounds
>good. Grease on the spindle; blue (or red) loc-tite on the threads;
>like John said you’re all set. Best to redo it every couple of weeks
>or so, or whenever you suspect them. When you redo, you need to remove
>everything, wipe them down, and refresh the gooey stuff.

U-Turn, are you saying that I should take the cranks off every few
weeks for maintenance purposes? I would be wary. Isn’t that in itself
bad for the threads? (Not the being wary but the frequent overhaul.)

Klaas Bil - Newsgroup Addict

“I thought about how mothers feed their babies with tiny little spoons and forks, so I wondered what do Chinese mothers use? Toothpicks? - George Carlin”

sorry to be negative but has anyone actualy cured a case of wobbly cranks?
in my experience the hub is destined to die as soon as the first wobble happens.
can they survive?

erin, i realise your talking about a freestyle unicycle but,
for trials rider the cycle seems to happen like this:

learn to do drops,
complain about wobbly cranks.
break/bend cranks.
buy trials unicycle with cotterless cranks
complain about wobbly cranks.
break cranks.
save for profiles.
buy profiles.
worry about somthing happening to expensive cranks/warranty etc.

unless your sensible of course and resist the temptation to risk breaking stuff.

Re: Re: Loose Crank

Yes, I’m saying that. More often depending on how you ride. That’s what I do. I ride between 10-20 hours a week.

It’s not bad for the threads. Bad for the threads is:


letting the crank nuts loosen and riding that way,

not using a proper fluid on the threads,

letting the crank nuts rust,

not riding the unicycle. :wink:

By periodically doing this, you have a chance to clean things up, ensure that the cranks are on properly, make sure that the uni is not rusting, check the pedal tightness, and so on. While you’re at it go over the entire uni checking your wheel for trueness, tire for proper mounting, air pressure, seatpost clamp for proper position, and so on.

It’s also a good idea to grease-up the seat post once in a while to keep it from seizing in place.

You’ll find that your uni is tighter, more responsive, breaks less often, and is generally in better health.

Oh, and when you replace the cranks, move them back a quarter turn; you’ll even out the wear on your tire.

Thanks for all your suggestions guys :slight_smile: . I took the cranks off this morning and amazingly the damage doesn’t look to be too bad at all :smiley:

I am going to put a set of different cranks on nevertheless. I’ll throw on a set of 127’s that orginally came with this Sem XL. Then I’ll see how everything settles in. If all goes well with the Sem cranks I may go back to the Doteks at a later date and go with your suggestion about letting them get reformed by the taper, Harper.

I am still hoping to find a torque wrench that I can borrow otherwise I’ll put the cranks on the greased taper with the ‘wood sandwich and hammer’ method. BTW, the right crank, which I had installed in the wood sandwich method three months ago, was just as snug as anything. In fact it took a bit of a muscle to even get it off, so I guess I have the knack at least 50% of the time :sunglasses: .


You may borrow my EXCELLENT torque wrench anytime you like.

I’m interested in the idea of applying loctite to the threads and then using a torque wrench. From my understanding, you should be using some type of molybdenum sulfide lubricant ( MoS ) on both the taper and the axle threads (and the nut). Otherwise your torque reading is meaningless. Applying the correct torque to properly lubricated parts is the only way to ensure that the parts are assembled according to design.

However, I personally question the taper specifications. I’m not sure that all cranks are given the proper taper. Without any banging or hammering, the crank should slip on to the axle approximately the same amount.

humm, nice offer… yeah, Seattle is only three hours drive away on a Sunday… :wink:


I’ve never heard of any MoS requirement (is that the abbreviation for molybdenum sulfate?), but if you supply a source, I’d be glad to look at it. The torque reading isn’t meaningless; it’s simply force applied at a distance. The torque is the torque. There’s no design spec that says 35 ft-lbs or 40 ft-lbs. That’s a number we’ve arrived at experimentally after guessing that it should be more than a bicycle’s bottom bracket. In contrast, the Magura brake installation manual has specified torque readings for this and that part; it says nothing about lubrication, let alone an exotic one.

By using a torque specification of our own with a given lubricant, and watching the results over many consistent installations on different cranks of different types and lengths, we come up with something practical. This is part of unicycling.

Using a torque wrench is much more consistent than pounding with a mallet. Greasing the spindle helps the nut push the crank on in a symmetric way so that the crank is more likely to be oriented properly. This method also avoids differences in strength, feel, and wrench length/style between unicyclists.

There is a lot of variation in parts. By using this installation procedure, we ensure only that the force exerted on the axle threads is consistent. I have had to return cranks merely on the basis that they did not fit on the hub properly.

If it doesn’t go on right, send it back. If you say that you pounded on it with a hammer, they might not take it back.