Schlumpf hubs: general discussion

I still do not understand whats wrong when the crank touches the spacer at 18 Nm. What stops you from tightening it the remaining 22 Nm? At which tightening torque would you expect it to touch the crank (40 Nm would be too late!). The spacer is not supposed to just be gently touched by the crank but to be clamped by the crank properly.

I also wonder.
On my Quax non geared 36er there is about no torque until the crank reaches the spacer (by memory, I didn’t measure the torque) , and then I put much torque so that the bolt stays at its place.
I don’t understand the issue with the 18Nm stuff.
Maybe the ramp of the spindle (isis like) is too “flat” to keep the crank from slipping , or the spacer is too weak to support the missing torque from 18 to 40 Nm, or it is too large.

I used gel-type super glue on the inside of the bearing cover. Worked fine for me. (I think that’s what someone else on the forum used, so I just copied them.) It was just the bearing cover on one side. I could see where there was glue there before. It was completely loose, and made a terrible scraping sound as it dragged against the frame. (Sounded worse than it was, but it got my attention!)

Thanks :slight_smile: I’ll give that a shot. I’m assuming that’s what that residue was that I found on there before. If you happen to need to take the bearing cover off to repack later, is it then permanently sealed on? I would assume you wouldn’t want to use any chemicals to break that bond once it’s made or it may dissolve the bearing cover. Perhaps that sound was just coming from the glue working its way loose and that cover scraping the frame.

For 2016 Schlumpf, Hub there is only one Size of spacers which is not appropriated considering the dispersion of ISIS standard on both axis and cranks; it’s why spacers are existing In 4, 5, 6, 8, 10mm for non Schlumpf hubs

The 40 Nm are part of the ISIS specification (see here) and not a special Schlumpf phenomenon. ISIS was originally designed with a crank stop, we use spacers as crank stops. It is not specified, at which torque the crank shall touch the cranks stop (spacer) but there is an amount of preload/ press-fit defined in mm.

(see here)


means: too little or no spacer can damage the interface


(see here)

So, if Silva needed 18 Nm to bottom out the crank, it did definitely not bottom out on the crank stop prior to attaining a press-fit with the spindle and everything shall be just fine!

40Nm Schlumpf specification is for pre-2016 hubs without spacer, I think this too much with a spacer; as soon as you are using a spacer, you don’t need such high tightening torque to avoid loosing your crank

About 40Nm are quite normal for the ISIS interface (the ISIS specification requires a crank stop).

These Bike ISIS interfaces all have an integrated crank stop and are supposed to be torqued around 30 to 45 Nm.

You can tighten cranks against a crank stop (spacer) with higher torque than cranks on a hub without spacers.

Silva has the unicycle/hub right now, so I cannot answer that question. I am relying on their expertise and the fact that they have installed many Schlumpf hubs in the past. They are the ones who told me that their tentative solution was to re-machine a part (spacer?). When Silva informed me of the problem, my understanding was that this problem would apply to any of the most recent batch of hubs. So, I wanted to share that with the forum.

Did they Try to fit another set of cranks ?

I don’t know, but I was wondering if a slight change in the cranks could have caused the problem. My guess, based on the fact that their other Schlumpf build experienced the same issue, is that the cranks were not the problem. But, cranks are definitely a place to consider…

Schlumpf Hubs have been machined surely In a unique batch
ISIS angle is 1 degree so a small difference on the cranks have great impact on the crank position

20" Schlumpf Update

I feel a little bit like Chicken Little, screaming “the sky is falling!” Anyhow, I just spoke to SIlva cycles, and now I’m really confused. Last week one of the technicians there said they could only tighten the cranks to 18nM, and today they told me they were now able to tighten it to 40nM. So, I am not sure what to think right now. Again, I’m happy to be working with Silva on this, but I don’t really understand why their evaluation changed. Sorry for freaking anyone out.

ISIS is a standard - if different cranks need different sized spacers then some of them aren’t meeting the standard. Different sized spacers for different hubs is reasonable, given that the ISIS taper might be positioned differently relative to the bearings. A Schlumpf hub should need a single spacer size for all cranks - the spacer size which provides a crank stop in the right position on the taper according to the ISIS standard.

You certainly don’t need different sized spacers with ISIS in bicycle applications, where you can mount any cranks to any BB with the same crank stop position used for all cranks (I still have ISIS on my mountain bike).

What do you imagine the advantage of using a lower torque value to be? I still see reports of people having cranks coming loose using ISIS - a higher torque value helps prevent this.

I’m not sure if there is Chinese whispers going on here, but as good as they might be, in this case I’m not sure I’d rely on their expertise with previous generation Schlumpfs, given that the ISIS interface has effectively changed, and what might have been necessary and worked before is no longer the case. As several others have queried - exactly what is preventing them from increasing the torque?

ISIS standard tolerances are too large, information from Roger Davies and thé y are machining parts with lover than Max Spec

Bike are using stopper machines directly on the Hub , no spacer. Spacer help to fit tightening torque even if splines contact is not perfect. Without spacer the only solution is to use high tightening torque to aboid crank loosing

Hanging a Guni from the wheel’s rim


Does anyone hang its Schlumpfed uni from the rim (upside down)?
I used to do that with all my unicycles until today, but after installing the schlumpf hub I’m afraid that due to its heavy weight, it may put too much pressure on the attachment point at the rim and weaken it with time.

What do you suggest?

Thanks :slight_smile:

The RIM and the hub are made to survive moderate jumps with a rider on it
Hanghing the uni bottom_up is definitely ineffective on their strenght or life period
Unless you wheeel is already in bad shape

Here’s a bit of background, after a long email discussion between Florian, Roger and myself.

From Silva Cycle’s perspective (as with any good professional dealer), he needs a consistent spec that is warrantee-able.

Some of the initial questions about how hard to tighten came from the question, how much torque is going to damage the spacer or bearing. Florian tested the hub with up to 50 Nm torque without damage to the spacer.

40Nm torque is more than enough to securely seat a greased ISIS axle, plus some redundant tightness to prevent the bolt from loosening. That is more important on the KH/Schlumpf hub than a standard hub because the axle bolt is hidden by the shifter buttons (e.g. harder to check tightness) and a loose axle + loose cranks likely = damaged shifter buttons or shifting rod.

It’s also worth mentioning the different perspective of a typical rider. This forum is a particularly well-educated group, but the majority of riders don’t even know what a torque rating is, let alone own a torque wrench. And no-one I know carries a big torque wrench on a ride. In many rider’s experience (including mine) a torque rating as low as 30 Nm (or even high 20’s by some reports) is enough to securely seat the ISIS spline; any additional torque just better secures the bolt against loosening. One of the good things about ISIS is that it is quite forgiving this way.

Last note: often it seems like newly installed cranks need axle bolt checking more frequently at first, then not so much.

Clarifying on my long-winded response: 40 Nm on a greased ISIS interface for the geared hub was our consensus spec. Up to 50 if you don’t grease it. Plus periodic checking especially after the first few rides.

This has been my experience with my other unicycles. It’s important for owners of new unicycles to understand that they need to check tightness more often…when the product is new…which is counterintuitive, because we may assume that something new doesn’t need adjustment.

I bought the Park TW-6 torque wrench. I will be checking the tightness of the hub bolts frequently on my 20" Schlumpf build. I didn’t realize how big the TW-6 would be; I’ll have to see if I can get it into my camel-bak.

Special thanks to Kris Holm. When I was planning the 20" build, he personally answered an email question I had about the KH long-neck frame Schlumpf compatibility…then I ended up going with the Nimbus Equinox frame. Kris’ devotion to unicycle design has helped raise the quality for all the major brands.