Author Topic: Anyone else had a problem with the new sprocket?  (Read 565 times)

onebikeoneworld

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Anyone else had a problem with the new sprocket?
« on: August 20, 2017, 09:42:00 PM »
I am now in South Africa, near Cape Town, and was riding down a hill on Saturday when the pedals stopped turning/locked up. I hit the brakes immediately and looked what had happened. The Thorn-installed Rohloff sprocket was loose and the metal clip that seemed to have been holding it in place had somehow come loose (the chain hadnít been super tight but also not that loose, and if a loose chain were enough to make what happen happened then itíd be a serious design flaw). I positioned the sprocket back where I thought it was supposed to go, used my leatherman to lever the clip on to hold it in place and tried to replace the chain. As you can see in the 3rd picture, that failed as the force had been strong enough to bend the chain, and in the 4th picture, you can see the damage to the chainring.

I fixed the chain but got picked up before I got to test the bike out (Iíll do so properly later on Monday). We got to the house I leant it against the other bikes. We get back from a day out today (Sunday) and my friends find a small lake of Rohloff oil had leaked out of the hub. Iíve had drips out of it before, but this was probably 10cm long and 2-3cm wide? I didnít get a good picture before my friend wiped it up. Iíll check the hub tomorrow but Iím hoping this is just because somehow that clip coming off caused the paper seal to stop functioning properly and caused it to leak out rather than actual damage to the hub.


Danneaux

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Re: Anyone else had a problem with the new sprocket?
« Reply #1 on: August 20, 2017, 10:19:26 PM »
I sent Dave Whittle at Thorn Workshops a tickler on this one.

My idle speculation is the sprocket retaining ring may not have been fully seated on the carrier when a stick or something may have flipped into the lower chain run, causing the chain to derail bending the links, popping the sprocket loose and damaging the area below the chainring tooth. This would have had the effect of stopping the cranks/pedals from turning and also resulted in the damage we see.

Just a thought, but it would explain the chain of events.

Best,

Dan.
« Last Edit: August 21, 2017, 04:10:28 AM by Danneaux »

martinf

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Re: Anyone else had a problem with the new sprocket?
« Reply #2 on: August 21, 2017, 06:01:23 AM »
I can see a small piece of wire through one of the chain links in the first photo. Could that have caused the problem?

Danneaux

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Re: Anyone else had a problem with the new sprocket?
« Reply #3 on: August 21, 2017, 06:48:40 AM »
Quote
Could that have caused the problem?
Sharp eyes, Martin. Maybe could've. It is right next to the sheared inner link plate. If it got sucked in, there might not have been enough room for the inner link and wire all on the same sprocket tooth.

I recall a post on the Forum some years ago, where someone rode through a grassy field and a bit of grass managed to prop open a seal, causing his Rohloff hub to leak.

Sometimes, it is the little things that get you.

All the best,

Dan.

onebikeoneworld

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Re: Anyone else had a problem with the new sprocket?
« Reply #4 on: August 21, 2017, 09:44:41 AM »
Good eyes indeed! Didn't see that at the time or even when I looked at the photos.

Dan, reading your theory makes sense. My only thing is I don't see how the retainer ring wouldn't have been seated properly. It was installed by Thorn themselves back in March and I can't think of anything that could have dislodged it since then. I like having an easier to remove sprocket, but if it can be ripped off, leading to the destruction of the chain and a complete oil leakage, simply by something jumping off a tar road into the chain then I'm not sure the design is as good as it could be.

If all of the oil leaked out is that a case of shouldn't ride at all? I've not got any spare oil with me as I recently did an oil change and am flying hope in 2500-3000km, but I can get in touch with the distributor in Johannesburg to see if they know any local bike stores where I can get enough for an oil replacement.

geocycle

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Re: Anyone else had a problem with the new sprocket?
« Reply #5 on: August 21, 2017, 10:37:24 AM »
Sorry to hear of the problem, the bit of wire looks likely to be the culprit.  if so, I'm surprised the chain didn't break before the ring popped off.

On the oil, the general advice seems to be that there will always be some oil in the hub coating the innards and enough to prevent damage until you get somewhere you can do an oil change.  One thing I'm not sure about is why the oil came out just be removing the sprocket as I didn't think this acted as a seal as in the old design, but I might wrong on that.
 

onebikeoneworld

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Re: Anyone else had a problem with the new sprocket?
« Reply #6 on: August 21, 2017, 01:49:01 PM »
Sorry to hear of the problem, the bit of wire looks likely to be the culprit.  if so, I'm surprised the chain didn't break before the ring popped off.

On the oil, the general advice seems to be that there will always be some oil in the hub coating the innards and enough to prevent damage until you get somewhere you can do an oil change.  One thing I'm not sure about is why the oil came out just be removing the sprocket as I didn't think this acted as a seal as in the old design, but I might wrong on that.

Do you think that's supposed to have the ring pop off?
The oil didn't come out immediately. My host-to-be came and picked me up to drive me the last 15km and it wasn't noticed until 24 hours later when the house had a funny oil smell. So glad that they didn't have carpet so it wiped straight up.

geocycle

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Re: Anyone else had a problem with the new sprocket?
« Reply #7 on: August 21, 2017, 03:20:34 PM »
Sorry to hear of the problem, the bit of wire looks likely to be the culprit.  if so, I'm surprised the chain didn't break before the ring popped off.

On the oil, the general advice seems to be that there will always be some oil in the hub coating the innards and enough to prevent damage until you get somewhere you can do an oil change.  One thing I'm not sure about is why the oil came out just be removing the sprocket as I didn't think this acted as a seal as in the old design, but I might wrong on that.

Do you think that's supposed to have the ring pop off?
The oil didn't come out immediately. My host-to-be came and picked me up to drive me the last 15km and it wasn't noticed until 24 hours later when the house had a funny oil smell. So glad that they didn't have carpet so it wiped straight up.

I'm just surprised that the ring was the point of failure, I would have thought the chain side plates would have gone first.   My guess would be that the wire jammed between the chain and the sprocket although I cannot understand why the split ring pinged off.
 

martinf

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Re: Anyone else had a problem with the new sprocket?
« Reply #8 on: August 21, 2017, 06:57:40 PM »
My own theory is that the wire, probably picked up on the tyre, derailed the chain, which then got caught between sprocket and hub, causing the circlip to jump off.

I've never looked very hard at the gap between Rohloff hub and sprocket - if my theory is correct there would have been substantial leverage in this gap, which might explain the oil leak - maybe some damage to the seal.

But perhaps less overall damage than would have happened with the old system, where the steel screw-on sprocket would in all probability have stayed on, and the chain plus bit of wire might then have chewed up the alloy hub shell.

I think this kind of thing is a rare occurrence on a hub-gear bike. Had it happen to me once on a derailleur bike, wire got caught in the derailleur, derailleur twisted into spokes and was ripped apart, causing slight damage to spokes. And seen it happen once to a rider in the same group as me.

I've had one chain derailing problem on a hub-gear bike in about 4 decades of hub-gear use - a very slack and very well worn chain jumped off the sprocket and into the gap between sprocket and dropout. Not sure whether I had picked up any debris that might have triggered the derailment. I remember it was hard getting the chain back on, but I managed it without removing the wheel, so the chain was very slack indeed.

Over the same time period I've had lots of chain derailing problems with derailleur bikes, with overshoots into the spokes or into the gap between small sprocket and dropout, and on bikes without front derailleurs the chain coming off chainring when shifting the rear derailleur.
 
If compatible with the chainring/sprocket combination, a Chainglider should be effective on a hub gear bike to prevent derailments caused by wire or other debris, but it might make a spontaneous derailment due to too much chain slack more likely, as it hides the chain from view.




 

onebikeoneworld

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Re: Anyone else had a problem with the new sprocket?
« Reply #9 on: August 21, 2017, 07:35:17 PM »
There was a bit more of an oil leakage today, so I'm not sure if the seal is damaged itself. I've taken the wheel off, removed the circlip and sprocket and looked at the seal and... I've no idea what it should look like so it's hard to say if it's damaged. Thoughts? Also as it's night it's hard to get good photos. When removing it, and cleaning the area, I did find some flakes of metal that you can see came out of the shell.

Danneaux

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Re: Anyone else had a problem with the new sprocket?
« Reply #10 on: August 21, 2017, 08:32:38 PM »
Just a word of kindly meant empathy here: 'Sure sorry this happened no matter the cause.  :'(

Bike scars are Tough; Rohloff scars moreso.

All the best,

Dan.

onebikeoneworld

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Re: Anyone else had a problem with the new sprocket?
« Reply #11 on: August 24, 2017, 09:46:17 AM »
To update people, the opinion is that the seal is damaged (it's still leaking oil a few days later) and that the cause was a loose chain. I'd tightened the bottom bracket maybe 800-1000km earlier, and if it's the case that whenever the chain drops you risk ripping off the sprocket and damaging the seal then I'm tempted to go back to the old style sprocket.

Thorn, with theire regularly wonderful customer service, have a parcel in the post to me to resolve the issue. Last I checked it has gone from Bristol to Brussels and has now departed Amsterdam and expects to be here in Cape Town on Monday (and hopefully gets through customs quickly). Then it's off to a local bike shop with some instructions in hand so they can give me a hand getting it going again. When I'm back in the UK at the end of October, the wheel will take a visit to Bridgwater and they can do a more thorough examination of the hub.

j-ms

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Re: Anyone else had a problem with the new sprocket?
« Reply #12 on: August 24, 2017, 10:41:04 AM »
Hi Dominic

How long did you go before you adjusted your BB  and how loose was the chain ?  I ran our chains for about 7000 or so kilometers before adjusting and the chain on my bike was pretty loose, Leigh's not so bad.  Almost all of those kays were on loaded bikes in touring conditions.  I was under the impression that so long as the chain wasn't falling off it was OK.  I know Thorn have their 40-60mm guidelines but I would prefer to adjust the BB as seldom as safely possible but if a loose chain was the cause of your sprocket coming loose I might have to re-assess my approach.

One other question.  Is there any way that the fall from Lionel's truck might have caused some damage ?

Jean-Marc


onebikeoneworld

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Re: Anyone else had a problem with the new sprocket?
« Reply #13 on: August 24, 2017, 10:49:57 AM »
I'd last adjusted the BB when I did the oil change, checking my GPS files that was 1200km of riding earlier. I don't think the chain was particularly loose, and when I fixed the chain (swapped 6 new links for those around the bent link) it didn't seem to be in a state where I'd have felt like it was going to come off repeatedly. With the old style sprocket, I'd usually go with the idea that the chain needed tightening when it fell off twice. If the theory that a loose chain caused this and can potentially damage the seal (which needs replacing using a specialised tool) then I'll have to tighten it more frequently than that. Dave said to me that he tightens his own bottom bracket quite frequently and my concern of two marks next to each other leading to grooves is less serious than I thought.

As far as the fall, that happened more than 3500km earlier so I don't think it should have been relevant, but obviously can not be 100% certain. However the leaking from my hub definitely did not start until the sprocket came off.

StuntPilot

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Re: Anyone else had a problem with the new sprocket?
« Reply #14 on: August 24, 2017, 11:45:25 AM »
Hi Dominic

Sorry to hear about the new splined cog problem. Been following with interest as I am considering moving to the new splined cog.

As for adjusting the chain I try and tighten it quite often but do not tighten it if I can still see the old indents through the eccentric bolt holes. This so far has ensured that the holes do not join up to make the eccentric unusable. I never wait till the chain comes off.

Hope you get it all sorted soon and enjoy your fantastic travels in Africa.

Cheers Richard (we met in Edirne, Turkey)