Thorn Cycles Forum
Community => Rohloff Internal Hub Gears => Topic started by: neil_p on February 26, 2018, 09:54:56 am
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Hey folks
I gave my Thorn an overhaul last summer:
Oil change
New chain (KMC)
New sprocket (and slim carrier)
New chain ring
New pedals
New bottom bracket
Ever since then I have had a vibration/grumbling from the drive chain, when pedalling in all gears.
The rohloff wheel has been back to SJS who confirmed it is fine ...
What next!?!? Could it be the chain is dodgy?
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A common cause of groans and creaks (that appear only when there is weight or force on the pedals) is insuffiently tightened crank bolts, so if it were my bike giving trouble, that's where I would start, torque wrench in hand. There is considerable disagreement about whether to grease crank bolt threads. You can ask for opinions here; I grease mine because if I don't, they creak, and I've never had one spontaneously unwind even though I torque them to only the lowest rating, 30N/m (you need to check what's specified for your particular cranks, or torque them to 35N/m which is a common lower limit for alloy cranks and not above the upper limit for any alloy cranks I know).
After that, from the easiest and most obvious causes:
I imagine you have long since checked that the chain isn't rubbing somewhere!
Have you fitted particularly fat tyres? If so, check by dusting the closed ends of the forks with talcum powder or rubbing on wax (one of your wife's decorative candles will do) and riding the bike, then checking what rubbed off from the fork to the tyre.
Does the width of your chain match your chainring? You must be very careful here. KMC makes chains with tiny variations in thickness (which many of us discover when we buy the wrong width of quick link), and the Thorn chainring (if that's what you have) is particularly thick presumably for reasons longevity.
Do you have enough slack in the chain? You should be able with the bike at standstill to depress the middle of the free run of the chain at the top by at least 10mm. A Rohloff flourishes on a much slacker chain than would be acceptable on another drive system.
Have you checked that the chain is running straight? Rohloff advises that the chainline should be within 1mm of straight. I mention this because, while you don't say which KMC chain you have, the single speed KMC chains are deliberately made very stiff from side to side as a factor in their longevity.
You may have a small amount of latitude from side to side in fitting the bottom bracket. After you've measured how far the chain line is off, inspect the bottom bracket; you want to know the length of the axle and whether there are any spacers already fitted, or space for you to fit spacers to put your chainwheel in a more advantageous position vis a vis the chainline to the sprocket.
If there is not enough adjustment on the bottom bracket, Rohloff used to give away with every gearbox a set of spacers which can be used with extra-long chain bolts for spacing the chainwheel; if you didn't get the chainring spacers with your bike, or have lost them in the years intervening, you can buy a packet of spacers from Rohloff dealers like SJS.
The last possibility I want to mention is that somehow you misfitted the bottom bracket. If that is the case, and you have corrected the problem while sorting out the chainline, you'll never know what precisely caused the problem, the chain or the bottom bracket. Small price to pay to have the problem gone.
If the problem isn't solved by this stage, and if you haven't taken off the bottom bracket, now is the time to take it off, and inspect it, and also the thread in the BB shell, thoroughly. When you refit it, use a torque wrench (common automobile type) especially on the nuts that hold in the pedal cranks.
If your bike still emits disturbing noises, it's gremlins, known where I live as leprechauns. Have you toured in Ireland, Wales or the Continental Celtic countries recently?
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i remember on my Look KX light carbon beauty i had this very annoying click every time i hit a certain spot,i was full sure it was coming from the wheel, i completely stripped the bike new cables bar tape regreased everything put it back together and still the feckin click click click :'(
problem was the outer bearings on the bottom bracket the BB shell wasn't faced so once i got that sorted bobs your uncle.
moral of this yarn get a new bottom bracket and be sure the shell is faced before you fit it.
anto
(expert on everything) ;)
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Maybe the new chain is slightly too tight. I have had similar symptoms when installing a new chain/sprocket on an old Sturmey-Archer hub geared bike.
There has to be sufficient slack in the chain at all crank positions - if everything isn't completely round there may be tight points. I forgot to check for these.
Solution (on Thorns) is to adjust the eccentric bottom bracket. On my old Sturmey-Archer hub geared bike, moving the wheel slightly further forward in the dropout solved the grumbling.
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be sure the shell is faced before you fit it.
On an external bearing BB, yes.
On a square taper BB the faces don't come into contact with the cartridge so having them faced would be pointless.
Either way a new BB would've been one of my first things to test, I'd have done that before sending the hub for testing. There's nothing lost if it isn't the culprit, just swap them back and you'll have a replacement ready for when you do need it.
Another thing, as martinf noted, is that chainrings aren't always perfectly round, do a google search on how to centre yours ("centering chainring" brings up plenty of advice) it's pretty simple. I shouldn't think this would cause your symptoms unless your chain is already too tight, but there's no harm in doing it.
Before any of that, I'd make sure the chainline is perfect, and I mean perfect, use the EBB to offset the cranks if need be, you can make long term adjustments later.
Could well be one of those things you kick yourself for when you work it out, we've all been there, good luck.
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Chain is this one:
http://www.wiggle.co.uk/kmc-x1-rohloff-compatible-chain/?sku=5360447194
BB is one of these:
http://www.chainreactioncycles.com/shimano-es51-octalink-bottom-bracket/rp-prod908
Chain is slack, needs tightening soon. The noise is like a purr (as if the chain is rubbing), rather than a creak or a groan.
Tyres very skinny slicks.
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BB is one of these:
http://www.chainreactioncycles.com/shimano-es51-octalink-bottom-bracket/rp-prod908
BB shell facing not required with those.
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Chain is this one:
http://www.wiggle.co.uk/kmc-x1-rohloff-compatible-chain/?sku=5360447194
BB is one of these:
http://www.chainreactioncycles.com/shimano-es51-octalink-bottom-bracket/rp-prod908
Chain is slack, needs tightening soon. The noise is like a purr (as if the chain is rubbing), rather than a creak or a groan.
Tyres very skinny slicks.
For a purr (unless you've run over a cat) I'd suggest something to do with the drive chain, ie the sprocket or chain or chainring has some sort of incompatibility or the chainline is out somehow. I'd swap these one at a time and see if you can eliminate the problem. I'm not familiar with the BB but potentially that could be a culprit.
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The KMC X1 is the top single-speed chain they make, with all the longevity goodies that also make the chain stiffer, so a chainline straight within the parameter or as near as humanly possible becomes even more urgent, and also whether the chain fits the chainring well, which are two closely related issues in that a skew chainline will aggravate any friction between a stiff chain and the chainring teeth.
Could you give us some idea of how loud the purr is, Neil. Your Rohloff sounds well run in, so it should be dead quiet in 11th gear, direct drive.
Dan: Why haven't we heard from Matt yet? Is he on tour out of communication somewhere? I thought he has worn out an X1, so he should know if it causes special problems.
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Dan: Why haven't we heard from Matt yet? Is he on tour out of communication somewhere?
<nods> Yes, he's touring Ethiopia at the moment and comms are scarce. He contacted me last night and is doing fine almost halfway through.
Best,
Dan.
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Neil is that BB new?
anto.
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The BB was new about 1000 miles ago. Chainring is thorn. Purr is quiet enough not to sound too annoying but I can feel it through the pedals. To make matters worse I do most cycling on a very good turbo trainer... So there's no wind / road / traffic noise to drown it out. Hub has had 10k miles use.
It feels like chain rubbing on chainring on sprocket... Or at least has the volume and feel I can imagine goes with that.
I will measure chain line again on the weekend... Surprisingly hard to do with mm accuracy!
When it's a bit warmer I also have old chainring, chain and sprocket... (Screw on type rather than new carrier sort). Will try swapping bits out to see where I get too.
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Ear Plugs - I'd believe SJS
Believe SJS what?
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Ear Plugs (the advice from my LBS when I took one of my bikes in which creaked and I'd changed and greased just about everything)
If SJS say it's OK then it probably is.
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yeah chainline is really tricky to measure. I have tried several times with wildly inconsistent results & no idea why!
Maybe try measuring the chain stretch with a tool... did you somehow get an old chain mounted by accident? Seems like all the obvious bases have been covered, so double checking strange things is probably what you're stuck with.
Did you just switch the type of sprocket, from screw-on to splined?
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yeah chainline is really tricky to measure. I have tried several times with wildly inconsistent results & no idea why!
Maybe try measuring the chain stretch with a tool... did you somehow get an old chain mounted by accident? Seems like all the obvious bases have been covered, so double checking strange things is probably what you're stuck with.
Did you just switch the type of sprocket, from screw-on to splined?
I bought new everything and fitted in one go. Went from a rohloff chain to kmc. Yep went from screw sprocket to carrier type. My first carrier was standard sort, SJS advised a switch to the slim carrier which I did.
The chain has been used for 1000m mostly indoors... If it's worn I want a refund! :)
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Ear Plugs (the advice from my LBS when I took one of my bikes in which creaked and I'd changed and greased just about everything)
If SJS say it's OK then it probably is.
Unfortunately they only checked the wheel which I'd posted to them. They haven't seen the whole bike, so although the hub itself has received a clean bill of health, lots of other factors still to eliminate.
They did say the original carrier (non slim) had worn on the sides, and changed for a slim carrier to improve chain line.
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It's easy enough to measure chainline with a cheap vernier caliper like this:
(http://uk.farnell.com/productimages/standard/en_GB/2311583-40.jpg)
(You can also get ones with a digital read-out)
1. Measure the diameter of the seat tube just above the chainring.
2. Measure the gap between the seat tube and the centre of the chainring.
3. Add half of measurement 1 to measurement 2 to find your chainline.
Even I have done it successfully!
The recommended chainline can be found here: https://www.rohloff.de/en/products/speedhub/equipment/
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They did say the original carrier (non slim) had worn on the sides, and changed for a slim carrier to improve chain line.
Now, by a process of elimination, we're probably there. It's very likely a still-skew chainline, with the effect aggravated by an extra-thick Thorn chainwheel, an extra-stiff X1 chain, and the extra width imposed by the new sprocket fixing method (even the slimmer one is wider then the original threaded one). What you're hearing is rather likely to be the corners being worn off the teeth of your gears by your stainless chain.
You need to fix your chainline by one (or more in combination) of these measures:
*spacers to bring your chainring into a straight line with the sprocket,
*refitting the bottom bracket with spacers to bring the chainring in line with the sprocket,
*or, possibly, if the chainline isn't too far off, a thinner chainring might be a temporary bodge (fit your old chainring temporarily and see if the noise goes away)
MEASURING THE CHAINLINE
The chainline is the distance from the centerline of the bike to centreline of the chain.
To measure the chainline take a measurement with the chain fitted at the front over the chain ring and at the back over the sprocket.
You might find your wife (or mother in law's) hemming measure a useful tool.
To use the bike frame and component hard points (as distinct from guesstimates about centres) as your references:
FRONT: Use vernier callipers to measure from the left side of the seat tube to the right hand side of the chain. Measure the tube diameter and the chain width separately. Subtract half the tube diameter and half the chain width. The result is the chainline at the front.
REAR: You should not have to measure at the rear because the chainline there is a published number you can look up for all the available and heritage sprockets.
RESULT: The difference between these two numbers is the distance you must move the chainring for a straight chainline.
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Plenty of advice for measuring your chainline, it can be a little awkward but take your time and it probably isn't as daunting as it sounds.
But before you start measuring, it's simple to check the existing one, it only requires a known straight edge, I use a piece of angle aluminium that started life as a bit of kitchen edging. If the straight edge sits flush on both the chainring and sprocket (Preferably in several places) it's spot on.
A friend uses a laser pen to check theirs, I haven't seen them do it but if you have one it can't be hard to work out.
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It's easy enough to measure chainline with a cheap vernier caliper like this:
(http://uk.farnell.com/productimages/standard/en_GB/2311583-40.jpg)
(You can also get ones with a digital read-out)
1. Measure the diameter of the seat tube just above the chainring.
2. Measure the gap between the seat tube and the centre of the chainring.
3. Add half of measurement 1 to measurement 2 to find your chainline.
Even I have done it successfully!
The recommended chainline can be found here: https://www.rohloff.de/en/products/speedhub/equipment/
Mine comes out as 56.5mm
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My chainline is off by about 5mm. I intentionally set it that way to have a bottom bracket spindle about 100 mm shorter than I would have needed for ideal chainline.
I suffer no ill effects from that chainline error, but I use standard 8 speed cheapo chainrings and the cheapest KMC 8 speed chains I can find. I have not tried the higher end stuff like you cite.