Another Broken KH Muni Schlumpf hub :(

Unicycles and Equipment
1

How much did I not want to join the broken GUNI club! :frowning:

AFAIK I’ve done everything by the book, even purchased a torque wrench ($$!) to tension everything correctly.

Waiting to hear back from Florian but the disease is:

With the crank nuts and buttons ON:

On the side with the knurled bearing, there is no spring loaded play in the shifter shaft. It engages gear then stops hard. (the button isn’t bottoming out, there is ample room for play)

On the side without the knurled bearing, there is spring loaded play in the shifter shaft but engaging the gear only results in freewheeling.

I thought it sounded similar to a problem Ken described earlier but:

With the crank nuts and buttons OFF:

On the side with the knurled bearing, there is now spring loaded play in the shifter shaft. It engages gear ok.

On the side without the knurled bearing, there is spring loaded play, engaging the gear still only results in freewheeling. OUCH.

In all instances the shifting is not as smooth or easy as it was when the hub was functioning, sounds different also. Something is not happy inside the hub I guess. No external sign of problems

Maybe I’ve somehow messed up, or it’s just one of those things. The hub has had less than 20 hours use on a 29, light easy stuff, getting used to the geared hub, learning shifting technique etc. I just had it built into a 36 wheel.

The main bummer atm is that I have been working on a long distance charity ride in a few months time, the geared hub is an important piece in that being possible. Due to weather conditions there’s really only a small window each year where the ride is possible.

I would’ve had a spare GUNI wheel made as a back up for the ride just in case - hard to find a Schlumpf tech in the middle of nowhere, but separate to the time involved in shipping the hub back and getting it repaired I guess it’s only natural now to wonder if the trade off in reliability with a GUNI is worth it for that kind of event.

Fingers crossed.

2

That’s a huge bummer. Keep us informed of what happens. I for one am very interested to find out what happened.

corbin

3

I am sorry to hear your hub has failed. Hopefully it can be fixed soon.

I was hoping to see one in action, I don’t think there are too many others in Victoria.

4

There are at least three I know of in NSW :stuck_out_tongue: Two of them sitting in my living room.

Sorry to hear about your hub Mal! Have you overtightened the bearing holders? I have a feeling that contributes to the freewheeling also.

5

Ken did the alternative set of buttons and crank nuts help the problem with your hub?

The bearing holder on the knurled side was tightened less than recommended in the manual, still tight but not enough to noticeably effect the spin of the wheel. (TBH the recommended torque settings in the manual seem excessive, 40 lbft on crank nuts especially… eek!)

It’s been quite hot here the last two days ~40C/105F… it’s a bit far fetched but is it possible excess heat could mess with the performance of the hub? The wheel sat in my wife’s car for several hours yesterday.

I wonder about the oil too. There was quite a lot of oil seeped into the paper when the hub arrived in December and it seems to weep oil. Could it hurt to give it a needle of oil now… I guess not. What do you think doctor? :slight_smile:

6

I’m not a doctor, but I do have some experience with this problem. My Nimbus 36 with the KH schlumpf hub had the same problem, and I showed it to florian in person at RTL (including the freewheeling). It happened when excessively tightening the bearing holders along with excessively tight cranks.

So, things to try, in this order:

  1. Does shifting work when the hub is out of the frame?
  2. Try loosening the bearing holders a bit
  3. Try using 30 ft-pounds on the crank bolts, not 40. I think 40 is too much. I use 30, and it has been working for me on my munis. I think James uses 25 ft-lbs on his, and hasn’t had any trouble with cranks coming loose.
  4. You may want to try another set of cranks – alumn will deform with too much force, and I think part of the problem is having the cranks too close to the frame, causing the inner shaft to hit the inner circle on the crank, allowing the wheel to freewheel.
  5. Use blue locktight!

Overall, I do think there is a problem with the hub – it should NEVER freewheel, but it seems possible to get it into this state.

corbin

7

Oh, and Hi Mal! I forgot that lunicyle was your login :slight_smile:
corbin

8

I think it is Pete actually. Mal is onebyone. Don’t worry, all these Aussies look the same to me too:)

9

You know those aircraft disaster shows, how they often point to a series of things that lead to the failure - I got to thinking last night and also had some luck! I think the above is all good advice, thanks Corbin.

Main thing I got to wondering is ‘how accurate is this friggin expensive torque wrench?’! I bet you it isn’t… I’m going back to doing things by feel for now. I’d never tighten anything up on a bike/uni that crazy tight without one of those things.

One the KH cranks I had on the 29 GUNI did appear to deform and slide way way too close the frame when I tightened it up to the spec of the manual after the first rides, just missing the frame. Warning sign.

Similarly the bearing holder on the knurled side at the recommended torque seemed way too tight. Another warning sign.

Getting that deformed crank off when it came time to get the hub built into a 36 wheel was a problem. I used an ISIS crank puller, from UDC here in oz. I was as careful as I could be not to mess the shifter shaft. Another warning.

The good news though is that the hub at least seems to work ok again for now anyway, how much is relevant to the outcome below I don’t know:

  • I gave the hub a needle of oil figuring it couldn’t hurt and might help.

  • I set the torque wrench aside and applied far less pressure on the bearing caps. The bearing cap on the knurled side is tight enough to hold the bearing steady, but not so that it impedes the spinning of the wheel.

  • I decided to try every combination of the 2 crank nuts and 2 shifter buttons (after reading Ken’s problems and the possible solution including crank nut/buttons). The initial attempt didn’t change the shifter shaft behaviour, but then a combination of nut and button worked!!!

  • I fitted a new set of cranks and applied far less pressure than via the torque wrench at the recommended setting.

  • I gently changed gears back and forth by hand, doing a few rotations of the wheel, checking the cranks after each gear change to make sure it was all ok. It didn’t seem to be shiftly gears sweetly but it seemed to be working ok enough to give riding a go.

Not feeling too confident though I put on some leg armour (for the first time!) and went for a ride for a couple of hours at the local reserve, in the process changing gears back and forth 50-100 times I’d guess, along with some low and medium speed runs in 1:1.5 (including one good crash in the dirt just from going too fast - glad I had that armour on!).

Everything seemed to work ok.

I really enjoy the feel of the 36 GUNI, much more than the 29 GUNI. The rotating larger wheel seems to even out 1:1.5 much better than the 29l, and you seem to have two genuinely useful gears on the 36. Though I didn’t ride the 29 GUNI for long, it almost seemed like I had no genuinely useful gears for the terrain I ride in - just one too high and one too low.

Not sure yet of Florian’s point of view, but from the initial email it’s sounding like at least some of it is shifter shaft/button/nut. I’m waiting to hear if he thinks it is worth sending it back for repair/examination.

TBH with the hub working I feel bad about having posted!

10

hehey, yes it isn’t Mal! Sorry Mal! :stuck_out_tongue:

11

LOL, oops! You guys need to sign your names more often :slight_smile:

corbin

12

I think it is good that you posted! It helps proove that “too tight” of a torque can be bad. I think that may have been the source of the problem, and I think Florian’s spec for ft-pounds is too high.

corbin

13

Aw :frowning:

And I’ve been thinking you were Mal for ages. I forgot it was onebyone.

14

I agree and maybe it is being made worse by the cranks.

I dug around and found the crappy photo I took after tightening the KH cranks to less than 40. One of the cranks slid in way way too close to the frame and hub (this crank was very difficult to remove). The other crank didn’t do anything like that at the same torque, was just as it should be.

I agree it’s possible to deform the cranks, and fit variations crank to crank, but I’m wondering if for GUNI we need cranks with ultra industrial precision ISIS fittings.

crank_deformed.jpg

15

I have pretty much no Schlumpf experience, and most of my cranks on bikes or unis have been square-taper, but FWIW:

My two new unicycle hubs are both Nimbus ISIS ones (the only experience of ISIS I’ve had), and they came with spacers to go between the bearing and the crank. When the crank bolt is tightened, the crank pulls onto the splines then stops against the spacer, rather than being forced really tightly onto the splines like a square-taper crank. The taper on ISIS looks shallower than on square-taper to me, so I’d expect it to be easier to over-tighten ISIS and force the crank too far down the taper (which is why I assumed the spacers were there). I’ve seen lots of pictures on here of ISIS cranks with no spacer, so perhaps it’s not the norm to use spacers.

I suspect the 40ft lb torque is probably for square-taper cranks and that he just hasn’t updated the instructions for the ISIS hub.

Would it be possible to use spacers between the bearings and the crank on the Schlumpf hub, like on a Nimbus (and presumably KH), or is it not practical on that design? Seems like it would stop all the “crank on too far/not enough” problems people are talking about.

Rob

16

I think it’d be nice if the schlumpf hubs had slightly longer axles. The original hub is the same - if the crank is slightly oddly shaped, or slightly overtightened, it rubs on the frame. Even a couple of mm would do the job nicely.

Joe

17

The Schlumpf hub doesn’t have spacers, and I specifically recommended this to florian, but he said there was a reason he couldn’t use them (I forget why).

The 40ft-lb was for the new muni ISIS hub. Older instructions didn’t have the torque rating; he added it in later after people started having trouble with cranks coming loose all the time.

corbin

18

Rubbing on the frame is bad, but the issue seems to be the inside of the crank having a slight lip – tightening the crank too much requires the buttons to be tightened further in, and they can catch slightly on this lip, letting it freewheel. That’s the real problem :slight_smile:

corbin

19

It seems like spacers are a violation of ISIS specs. ISIS has a tapered spindle, and as with square-taper cranks, the crank is held onto the spindle by the pressure of the two surfaces; the crank bolt is there to keep the surfaces pressed together. If there is a spacer between the crank and the frame, the bolt will press the crank against the spacer, not against the spindle. It might work temporarily, but there would probably be slop in the system (since the crank isn’t tight against the spindle), and it would probably work itself loose over time.

The problem is poor tolerances on the hub spindles, the cranks, or both. I’ve never seen an ISIS-outfitted bike with spacers on the cranks.

20

Torque wrenches can cause more trouble than they are worth. The recommended torque settings for a component are often the dry torque amount but in reality you may be using threadlock, anti-seize, or whatever, at which point the torque wrench will register after more turning of the fastener. Also, you want a torque wrench where the setting you are after is more or less in the middle of the range, otherwise the accuracy is nowhere.

Norbar do a bike specific model. It is pricey, and you have to use it wisely, but it can be useful eg, for carbon parts.