KH Spirit crank loosening

Hey there,

Yesterday on the first ride on one of my unicycles, I noticed when I reached the bottom of the trail that my right hand Spirit cranks (with the disk mounted) was loose enough that I could wiggle it, though the bolt was still in.

I tightened it about 1/4 turn or so, and it seems tight now after riding around the parking lot real quick to check.

I’m using the stock spacers supplied with the hub, so that shouldn’t be a problem.

My biggest concern is that I don’t know how long I rode with the crank loose. I stopped at the top of the trail because I felt something moving, and ended up tightening the bearing clamps (that were a little loose too). Now I’m wondering if that crank could have been loose up there. That means that I would have ridden ~4 miles of down hill with it that way.

What are the chances that I could have damaged or stripped the crank?

It does seem like usually on a new unicycle I have to tighten the bearing clamps and cranks a couple of times before they stop working loose, but this is the loosest I’ve ever had a crank.


I can’t speak to damage but I have four unicycles with Spirit cranks and one set was just bad and needed to be replaced. The behavior was that the bad crank would sink down to a certain point before tightening and its (good) mate would not sink nearly as far. It was like a 5mm difference. It was obvious when I swapped the cranks as a test.

Best way to know about damage to the threads is to inspect them closely. Clean the threads on the bolt and inside the hub (my favorite spray of all time is brake cleaner for that), and then look for damage with a lamp.

If the threads are fine, I would just reinstall everything and use blue Loctite on the threads. One thing you could try before that is to reinstall a crank without its spacer and see how far it would go. That will tell you if you can go one size down on the spacer - in theory, hubs are slightly conical, so the further the crank can go, the tighter it would be. Try that on the opposite side of the brake, that’ll be easier.

I noticed that KH cranks are machined just a touch over the hub size. In other words, I don’t need a crank puller to remove them - unlike on my Nimbus. Which means they can become loose, and when they do, they quickly get a lot of play.

You need a thinner spacer between your crank arm and bearing. If your crank is loosening or when you pedal you feel a slight creek from your crank, the spacer is to long. What’s probably happening is your tightening the crank to the spacer but the crank arm is not fully seated. Try a couple of mm smaller spacer.

ISIS standard has too large tolerance for mass production, depending on your hub and cranks combination, you might adjust the spacer, I have the full set at home (4, 5, 6, 8mm)
One useful thing to check it : put your spacer and adjust your crank with hand (no tool), usually I consider 2mm gap between spacer and crank is fine for tightening with my wrench, if you have less than 2mm gap, put a thinner spacer
You can realize your own spacer using a 27.2mm KH seat post
Enjoy !

Okay so pretty much what I figured.

If I back the bolts off, I can wiggle the cranks but can’t pull them off (they just move).

I currently have 4mm spacers on it (which are stock with the hub). I put some 2 mm spacers on, and could no longer move the cranks.

Problem is, with smaller spacers, my rotor rubs the disk caliper adapter. So basically 4mm is what I can use.

If the bolts are tight there is no movement. Should I just loctite them and check periodically that they are still tight?

No other choice without changing your cranks !

The stock KH have indeed 4mm spacers, and having thinner is probably doable without a disc brake. In theory, it was worked out when the uni was designed and the tolerances are pretty low.

So yep, Loctite is the way to go. You can always flip the wheel around before doing that, maybe the non-disc side of the wheel has less play.

Yeah and I’m not aware of any other crank choice unfortunately.

That’s more of a hub/crank combination.
I recently put together a franken-uni with parts I had laying around, and a complete wheel bought on this forum (KH rim and Nimbus hub). When I put my KH cranks on it (Spirits, like yours), I was surprised to see that they were sitting pretty tight before I even put the bolts in, and I definitely needed the extractor to remove them.

I would drop red locktight on the ISIS interface. That will make the crank tight on the interface of the hub. That’s what I do with my spirits so I’m 100% sure the disk side doesn’t move and rub on the brake. My first set of spirit came loose a few times. It was annoying. I’m not taking any chances now.

Jakob, thanks! I will definitely do that.

So next question is what are the chances I rounded out the cranks to some degree riding on it loose?

Just got done putting red loctite on the isis interface and blue loctite on the bolts. Hopefully it stays and I didn’t drip any loctite into the bearings :roll_eyes:

Sounds like a good idea, but what is “red locktight”? I only know the blue and in particular I presently only have the German brand “Uhu” or something like that (which is also blue). Is the red different and less strong or something? Or can I use normal blue locktight on the ISIS/crank interface?

I am not having loosening problems per say, but I have some pretty significant creaking on my 36 and I don’t think it’s the spokes… everything points to the crank-bearings interface as the source of creaking. I think I reduced my spacer width a while back, but maybe the locktight idea is worth a shot. Next question: if my cranks are staying on and not actually loosening where there is any play (that I can feel), is it damaging anything to creak? i.e. if it is just annoying then I can live with that, but it seems like the creaking would be wearing something more than it should…

Loctite comes in three (maybe more?) strengths: purple (low), blue (medium), and red (high). Red is supposed to be for joints that you never want to take apart. Or hardly ever. Like, things may break rather than come apart. But in some instances, it’s the stuff to use. Just be judicious. And careful.
You can use blue Loctite on the crank/axle interface if you like, but you may not notice any improvement. It’s main job is to prevent vibration loosening.
edit: for best results, make sure the surfaces are clean before applying.

And green. This stuff is like water, and made to wick in to preassembled fasteners. It is stronger than blue, but still removable (not great on super fine threads).

pretty sure the green is for bearings etc
I’ve never tired it on threaded things…

and if red is used correctly it requires heat to remove the nut/bolt.

Loctite makes many products and there are only so many colors! Numbers can help to avoid confusion.

290: Medium strength wicking threadlocker (green)
609: Bearing mount retaining compound (green)

222: Light threadlocker (purple)
242: Medium threadlocker (blue, the most common stuff)
271: Heavy duty threadlocker (red)

Etc, etc, …

Either way it has seemed to work so far (knock on wood).