How to tell cranks are tight enough?

Hello all,

I did a search and found nothing that helped me ease my mind :stuck_out_tongue:

Here’s the thing: I own a Sun 24" MUni. Within a few weeks of riding, the original cranks pedal threads stripped and the pedal came off while riding! Scary. I went to the bike shop and they were able to “helicoil” the threads so I was back to riding. Unfortunately, it did not last long and the helicoil stripped the same as before. Instead of dumping money into these cranks, I picked up some 165mm Nimbus cranks.

Here’s the thing: the ISIS spindle off the hub was too long… it extended past the crank so the bolt that holds the cranks on tightened against this rather than against the cranks. (I should note at this point that the cranks slipped on and off with little effort.) Perhaps it was not a good choice, but after much frustration i took a handfile and filed off 2-3 mm of the spindle so the bolt tightened against the crank. This helped and the cranks weren’t as wobbly.

So now, in the last week, I decided to buy new cranks. They are 127/110 mm dual hole Moment’s. To my surprise, these cranks would barely push onto the spindle (as opposed to how the Nimbus cranks slipped on and off.) So I pushed them on as far as they would go, then tightened the bolt down on them as tight as I could. (Here’s praying that none of this was the wrong thing to do :))

Now my question: Is there a way to tell if my cranks are tight enough? I’d rather not ruin another set of cranks, especially not KH moments!

Sidenote: I have rode on these cranks for about 10 miles since installing them and haven’t noted any wobbling in the cranks or creaking noises.

Thanks for your help!

Are you sure the Sun is ISIS?

It sounds like the parts are not compatible. Can you post pics?

I certainly can, I will have to wait until I can get home but I will get pictures up.

Although I am a newbie to unicycles and unicycle maintenance, I’m fairly certain they’re ISIS drive!

Happily, I was able to get back from the University sooner than I thought! I took a few pictures. Unfortunately I lack a crank puller and was unable to get the crank off (perhaps a good sign?) Anyway, here’s the pics:
First Image: Attempted close up of the interface.

Second Image: Shot from further away to give the “big picture.”

Third Image: Top view to show how far the crank is on.

*Edited for image size.

Some cranks and axles are not a good match as the taper is very slight so any slight difference in tolerance or worn surfaces can make them go on too far. Also due to the bearing size Unis use the required crank stop step that should be machined into the axle that the crank should butt up against isn’t able to be used so a spacer ring that slides on the axle between the crank and bearing inner race should be used (which you do not have).
Without this spacer cranks will creep further down the axle taper until as you found you bottom the bolt out on the axle

You seem to have a very long axle on that hub so you would probably need a two spacers on each side (maybe a 2x 5mm? but you may want to measure the gap and get two that take up the space plus a fraction more so the cranks can be torqued against them). With these and some blue loctite on the bolts you may be able to save the situation but you may have to get some new cranks that are less worn (the cranks are soft Aluminum unlike the hard CroMo steal axle so the cranks will most likely be the worn part)

Cranks and Hubs are a bit hit and miss to be honest I have lots of different cranks and none of them it in the same place on my hub hence I have a collection of different spacers with different widths

Hope that helps

Thanks, it help so much! As I said, I’ve only rode about 10 miles (this was all one very long ride) so there I don’t believe the KH cranks I have on should be damaged much, if at all. I didn’t know about the “spacers” because the only unicycles I own are cheap Sun’s. I will look into it and make sure to invest in some.

Thanks so much :slight_smile:

Edit: Right after I posted this I went on UDC and found some spacers :slight_smile: I ordered them and I will have to hold off on riding until they arrive.

Thanks again!

Sounds like your earlier “crank tightness” problems were at the pedal end. This usually happens because the cranks are on the wrong sides. Make sure you’re riding with the right crank on your right, or your pedals will come loose again.

With practice/experience, you learn to notice when pedals aren’t tight. There’s a little bit of movement as you pedal. If you ever notice this, stop riding immediately and try to get the pedal tightened. Otherwise you’re eating threads with every stroke.

At the hub end, sounds like you’re plenty tight now. I don’t do much with ISIS since most of my unicycles are older, but a general rule of thumb is to check the tightness after the first few rides, to make sure nothing’s coming loose. Both pedals and at the hub.

When I ride my square taper unicycles, either on road or trail, I always give those axle nuts a little yank to make sure they’re tight before starting out.