Problem with the crank-bolt.

Is it normal that cranks bolt keep coming loose?
Maybe I need to buy news cranks, but they are so expensive for me :thinking:

The photos:


Not normal.

Take the crank off, clean the surfaces, fit the crank carefully, strike it firmly with a wooden or rubber mallet to bed it on, tighten the bolt, ride for a few minutes, tighten it again. It should not come loose in normal use.

It shouldn’t come loose, but it’s not an uncommon problem. Are you installing and torquing the cranks per the Schlumpf instructions?

It also looks like your brake pad doesn’t sit in the right position and only touches the outer half of the surface it is supposed to break on. Maybe you used the wrong adapter? Or used the right adapter upside down?

Looking at the picture, I don’t see any additional spacer in your setup. Is your Schlumpf hub one of the most recent, 800 series? Florian redesigned the latest hubs so spacers can be used. Neither I, nor the bike shop who built my geared unicycle – were aware of this design feature – when I first got my guni. I learned about it a year after getting the 800 series hub from an email Florian sent to the 800 series owners. Perhaps the information was there all the time, but I didn’t take seriously enough the need to learn the mechanics and specs of the hub. Shame on me…

Anyway, I installed spacers, and since then, loosening of the bolts has stopped being a serious issue. As Florian and others explained, the 1% flare in the ISIS specification, sans spacers, is not enough to avoid the cranks easing their way inwards toward the hub. That may be the reason your bolts are coming loose.

I carry the following tools with me when I’m riding on my Schlumpf: A small socket wrench for the crank bolts, the torque driver for the buttons, and the small tool for stopping the buttons from spinning.

Aren’t the 800 Series hubs delivered with spacers? And weren’t these even special spacers?
Look at the Pictures here:

I put some another pair of spacers on my hub. I guess there are spacers on the 800 series, though they don’t look like the spacers I’m used to. When I tightened the crank bolts to the proper spec, with the original spacers, there was still a gap between the cranks and spacers; this, I think, was the cause of the loosening. After installing the second set of spacers, the problem disappeared.

Sorry for the confusion.