Thorn Cycles Forum
Technical => Transmission => Topic started by: Matt2matt2002 on September 28, 2013, 07:05:16 pm
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Just adjusted my bottom bracket to take up excess slack in chain.
Many thanks to all who offered advice.
Quite happy with the result. Not too tight and no where near as slack as when it came off!
This afternoon was sunny and warm in Aberdeenshire so my Raven was treated to a well earned scrub down and thorough clean.
Left to drip dry after a rub down with a towel and then parked in the shed.
As I pushed the old girl into the shed I noticed the pedals revolve. Not all the time but certainly a few times.
Does this indicate the chain tension is........?
Good/bad?
Are factors like chain cleanliness likely to influence this?
More drag?
Thoughts folks please.
Matt
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Does this indicate........?
Most likely it simply indicates the hub seal on the cog side is in good working order, Matt. Rohloff say you can drip a bit of oil between the cog and seal to minimize this "self driving" effect, but that has the drawback of attracting dirt and grit. I've decided to leave mine as-is. Already, the effect is less than it was, and will likely improve with further use/wear.
The fact it doesn't do it all the time is proof you're on the right side of things. A very stiff freewheel action with constant pedal lockup and a quick coast-down would indicate the shims need a single whack of the axle with a soft-faced mallet to reseat and put right.
I think yours is fine at this point.
Best,
Dan.
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Perfectly normal on a rolhoff. Mine always rotate and have done from new. As Dan says it's to do with the seals. It was odd at first but after 7 years I don't think about it. I do a lot of miles off Tarmac so it's probably due to build up of crud as much as anything.
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Checked chain today and the slack has reappeared.
Very strange indeed.
Quick look underneath and the 2 screw adjusters are still there and are tight.
Any thoughts? Time to remove a link and adjust bottom bracket accordingly?
Will I be doing any harm running the chain slack?
Matt
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IME a slack chain is fine, up to the point it starts jumping off the sprocket.
I don't understand why the chain suddenly went slack on you unless something wasn't seated properly, or you have an asymmetrical sprocket/chain ring with one tight spot and one slack spot... Check to see if the tension changes as you rotate the pedals. I'd not heard of this before I bought my current chain wheel / sprocket, one of which is not perfectly round! As the sprocket is made by rohloff my suspicion is the Surly chain wheel.
I'd make sure I used up all the range of the eccentric before removing a link. Remember to remove a link you are effectively removing a pair so you can easily over-shorten the chain. If you use the full range of the EBB you should be OK.
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A Rohloff chain is run slacker than most people ran the chain on their previous bikes. As Geo says, any slack in the chain short of jumping off is good slack. The bad adjustment is making the chain too tight: Rohloff actually has a warning about too-tight chains in the manual.
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Hi Matt!
I can only second the excellent replies of others, but I keep coming back to the re-loosening and suspect the BB bolts may not have been tight enough to hold the eccentric firmly in place under load, so it rotated rearward to the "old" spot.
If you're curious, you might wish to remove one or both bolts and peer down the bosses to see if there are signs of "skidding" -- where the eccentric rotated back to its old place.
The stainless steel bolt ends are pointed and hold fast by embossing the softer aluminum of the eccentric. If only the very points make little divots, it may not be sufficient to hold the lot in place. By any chance, do you have access to a torque wrench?
Best,
Dan.
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Sorry Dan, no torque wrench.
Can you clarify what I should look down and see?
When I last adjusted the bottom bracket I tried to look down the holes with the bolts removed and couldn't see anything. It was so dark! Should I use a torch?
Also, please clarify; the bolts are pointed, and it's the points embedding in the soft aluminium that hold things tight?
Pleased to hear so many folk run their chains slack.
I will,try to measure the rise and fall of the chain.
Matt
Who is 60 today but feels 16 (and who sometimes acts it - says Mrs. Matt)
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Hi Matt!
Happy birthday! This marks the start of your own personal new year, so Happy New Year as well!Can you clarify what I should look down and see?
I...have photos posted here: http://www.thorncycles.co.uk/forums/index.php?topic=5569.msg30297#msg30297When I last adjusted the bottom bracket I tried to look down the holes with the bolts removed and couldn't see anything. It was so dark! Should I use a torch?
<nods> Yes, that helps...or a camera flash, but then one has to look really quick! ;) Also, please clarify; the bolts are pointed, and it's the points embedding in the soft aluminium that hold things tight?
Exactly! Those photos I linked to above should help.Pleased to hear so many folk run their chains slack.
I will,try to measure the rise and fall of the chain.
For the other half of the question -- how tight? -- this thread may help: http://www.thorncycles.co.uk/forums/index.php?topic=5569.0 I run my chain at 10-12.7mm at the tightest, having first worked to remove any tight spots in the chainring mounting. The helpful word from Thorn via Dave Whittle is here: http://www.thorncycles.co.uk/forums/index.php?topic=5569.msg30361#msg30361
Best,
Dan. (...who is well into tomorrow already today)
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Thanks Dan, and as you can see, being 60 makes you do things twice when you,think you've done them once!
Matt
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;D
All the best,
Dan. (...who fixed it for you)
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Matt,
**HAPPY BIRTHDAY**
just think of yourself as two 30 year olds :)
Julian.
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Matt,
**HAPPY BIRTHDAY**
just think of yourself as two 30 year olds :)
Julian.
:D
Thanks Julian. We have the same sense of humour.
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Blow me down!
It's happened again.
The chain went really slack over the past 4 weeks and today jumped off when I hit a bump.
No probs putting it back but what's going on?
I know a slack chain is much better than a tight one but I would like to know what's happening.
The chain cannot be 'stretching' ( I know it's rollers and links etc.) but something must be shifting.
The bottom bracket? But how come?
Anyone else had a chain go from OK ( not too tight - honest ) to so so slack within 3 months.
Checked my mileage and since November last year I have done 1,500 miles - not touring with panniers - just recreational riding.
Matt
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Hi Matt!
It may be the BB grub screws are not (or were not) set tightly enough to hold the eccentric in place.
Or, it could be the eccentric has become scarred from past movement or too-close adjustment and the is no longer enough material for the grub screws to secure properly. I think I'd be inclined to pull the crankarms, remove the eccentric, and have a look.
A 15mm wrench will fit the grub-screw heads.
Alternatively, you could just invert the bike, remove the screws, and have a look down the holes to see what's going on in there.
In any case, the eccentric doesn't seem to be secured properly.
Best,
Dan.
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Good advice. I'll get the eccentric out and take a proper look.
I could never get a good look down those pesky holes, even with a torch.
Am I correct in thinking its the points that bight into the eccentric and stop it moving?
The 2 bolts themselves don't tighten any thing?
Think I've asked this before.
Matt
If I need a new eccentric, are we talking big bucks?
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Good advice. I'll get the eccentric out and take a proper look.
I could never get a good look down those pesky holes, even with a torch.
Am I correct in thinking its the points that bight into the eccentric and stop it moving?
The 2 bolts themselves don't tighten any thing?
Think I've asked this before.
Matt
If I need a new eccentric, are we talking big bucks?
That's correct Matt, the screws bite into the thick aluminium. If they are not tight enough they could move. You'll see this by scoring channels on the EBB. If you need a new EBB they are £30 http://www.sjscycles.co.uk/eccentric-bottom-bracket-insert-fits-raven-tour-mk1-sport-tour-only-prod11656/ (I recall you have the raven tour) but, I have a brand new unused one I could sell on as my new RST frame is different. I doubt you will need a new one but pm if you want to give it a go. Nb you will need to remove the bb from the old shell which can be a challenge! Are you using the C spanner to adjust? Final thought is the EBB in the right way round... Text on sjs site says:
'NOTE: circular manufacturing mark by 3rd cutout to go on chainring side.'
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Thanks.
I have never removed the bottom bracket and since the fault occurred after 2,000 miles I would guess its in the correct way.
I'm not clear on the last line of your post. Where can I read the full text?
Thanks for the offer of yours. I'll remove the bracket and post some pictures Last time I tightened it, I think I felt as if it would slide out ok. Why might it be difficult to remove?
Re the spanner. No. I dont have one.
I loosened the 2 bolts and the turned the bracket by hand. Held it firm and then tightened the bolts. First time the chain finished up too tight so fiddled about a bit and second or third time, it stayed slightly slack.
By using the spanner would I have avoided the fiddling about?
Matt
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Not sure what the problem is exactly. But one thing I would say... do not tighten the bolts and then fiddle about. Once you have tightened the bolts you have committed yourself - you have made a dent in the EBB that is not going anywhere. If you then loosen the bolts and fiddle a little and retighten the bolts, you now have two very closely spaced dents that have most likely merged into a funny sort of oval. You don't want an EBB that has funny ovals. You want nice discrete circular dents.
The EBB should slide very easily through the frame once the bolts are loosened. You might be able to slide it over far enough to get a really good look at the dents. But that is different from removing the "bottom bracket". The actual crank bearings of course are fastened inside the EBB. I have yet to venture into that business myself. I have seen some youtube videos where wrenches go flying. Those threads can be pretty snug. You certainly need the right tool corresponding to the bottom bracket bearing set on your bike.
I use a head lamp when I am messing around with the EBB. Probably that is why I manage to look down those little holes and can see what is down at the bottom. The head light is very close to my eye so I can see down the hole while the light can get down there at the same time. I find this very useful. I unscrew one of the bolts all the way and then fiddle with the position until I like the tension on the chain and also so I can't see any other dent in the EBB down the hole from which I have removed the bolt, or at least any dent down there is barely peeping off to the side. Either that or there is an existing dent right in the middle that I will reuse. I will loosen the chain a bit until I find either open territory or an existing dent that I can reuse. That might make the chain looser than I really want but that's the deal here. Precise tension is not possible. Properly spaced dents in the EBB create discrete steps and you just have to pick from the available steps or create a new step that is plenty far from existing steps.
I generally do end up fiddling about with the chain tension but I don't tighten the bolt until I am done fiddling. Of course this means the stupid EBB can slip while I am fiddling so that means triple the fiddling but c'est la guerre!
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Thanks.
I have never removed the bottom bracket and since the fault occurred after 2,000 miles I would guess its in the correct way.
I'm not clear on the last line of your post. Where can I read the full text?
Thanks for the offer of yours. I'll remove the bracket and post some pictures Last time I tightened it, I think I felt as if it would slide out ok. Why might it be difficult to remove?
Re the spanner. No. I dont have one.
I loosened the 2 bolts and the turned the bracket by hand. Held it firm and then tightened the bolts. First time the chain finished up too tight so fiddled about a bit and second or third time, it stayed slightly slack.
By using the spanner would I have avoided the fiddling about?
Matt
The last line of the text is from the SJS link to the EBB shell. I just quoted it verbatim.
The EBB will be easy to move side to side or remove completely if you take a crank off. It is the bottom bracket inside the EBB shell that I have found more difficult to remove from the EBB shell. You wouldn't need to remove this unless you decided to change the EBB shell.
It is much easier with a c-spanner. I have one I don't need so pm me and I'll send it to you.
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Many thanks to all those who have contributed so far.
I hope the following doesn't try your patience too much.
First pictures shows bike upside down ready for me to attack the EBB
Think you'll agree the chain is on the slack side? It jumped off a couple of days ago.
(https://lh6.googleusercontent.com/-v_RPmuzRKd4/Uwj85Zd6g_I/AAAAAAAABcU/F4KvUIQRGWo/w958-h719-no/EBB+002.jpg)
Next up I tried to remove the crank arm. Bolt out no problem but then it would not slip off. I have a rubber hammer and gently tapped it. Then I bit harder but no go.
Are they tough to remove? Any tricks to this game?
(https://lh6.googleusercontent.com/-cJBPaNQYHFg/Uwj8m_nKnjI/AAAAAAAABcI/2YvMkvQ6Mfc/w958-h719-no/EBB+001.jpg[img]Chain looks a bit rusty but I do clean and oil on a regular basis - honest.OK - next up was removing the 2 bolts. Both can away quite easily. Made me think that they had not been tightened up enough - or not biting as they should.Next 2 pictures show the EBB slid out as far as I could with one crank arm still in place. 2 slightly different angles.I can see where the bolts have been and certainly one indent was well off to the side. ( not me - honest :-\ )[img]https://lh3.googleusercontent.com/-EFt3BVpzUXM/Uwj9L51Jo4I/AAAAAAAABcc/nQijWWPrA5s/w958-h719-no/EBB+003.jpg)
(https://lh6.googleusercontent.com/-Lds7uQkDMjU/Uwj9dFMVzsI/AAAAAAAABck/8AIDAEBqVIM/w958-h719-no/EBB+004.jpg)
Decided to put everything back together and pay attention to centering the EBB through the frame ( bottom bracket hole? whats the correct name please?)
Next 2 pictures show how it sits now.
Even?
(https://lh6.googleusercontent.com/-sfiAu9xrAQU/Uwj97fbg7vI/AAAAAAAABc0/2REVlpdI70c/w958-h719-no/EBB+006.jpg)
(https://lh6.googleusercontent.com/-eS62jnn_gPM/Uwj9r6WSJrI/AAAAAAAABcs/GoKliRCmiTU/w958-h719-no/EBB+005.jpg)
That's it folks.
Chain reasonably tight - well, not so slack I think it will jump off.
Must say it can be very tricky when it happens - especially in traffic.
Comments and thoughts please.
Matt
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You need a crank extractor to remove the cranks, unless they are self extracting bolts which by they aren't by the sound of it.
The indents on the eccentric BB look reasonable but a couple are doubles which may be close enough together to cause slippage in use.
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Just noticed one of the pictures didn't come out. The one showing the bolt out of the crank arm.
I was expecting the arm to come off having removed the bolt.
Am i right or wrong?
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Matt,
Please don't use a hammer in an attempt to remove the crank. The crank socket has been wedged onto the square tapers of the bottom bracket spindle, so it won't simply slide off when you remove the bolt. Rual is correct; you need a crank extractor.
This should help going forward: http://www.madegood.org/bikes/repair/remove-a-square-tapered-crank/
I would suggest removing the chain before attempting to remove the crank.
All the best,
Dan.
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Thanks Dan.
I don't have one of those removers at the moment.
So am I correct in thinking that I won't be able to remove the EBB completely u less I remove the cranks?
I was able to slide out the EBB a little to see the indentations into the soft EBB.
One of the pictures shows an indent off to the side. Not good?
Re relocaring the EBB; just use a good wye to line things up?
The last 2 poctues show slightly different views of my final setting of the EBB. Even?
Thanks
Matt
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You cannot remove the EBB completely without removing the crank. You need a crank puller described above to remove the crank. It's really important to screw the crank puller tightly and squarely into the crank before attempted to extract it otherwise you can easily strip the crank threads. Definitely worth looking at some videos online first or ask your LBS. To remove the bottom bracket from the eccentric bottom bracket shell you need another tool (or ask your LBS). But, looking at the dents I think the EBB is fine. I just line mine up so the vertical surfaces are flat against the edges of the frame as I think you have done.
Sometimes the EBB can move when you tighten the screws and some tension is lost. The bespoke spanner will help!
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So am I correct in thinking that I won't be able to remove the EBB completely u less I remove the cranks?
I was able to slide out the EBB a little to see the indentations into the soft EBB.
One of the pictures shows an indent off to the side. Not good?
Re relocaring the EBB; just use a good wye to line things up?
The last 2 poctues show slightly different views of my final setting of the EBB. Even?
Matt, where are you in the UK? you need to speak to a bike mechanic who can advise you/keep you right, do you have a LBS? ??? Dave
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you need to speak to a bike mechanic who can advise you/keep you right, do you have a LBS?
Agreed. Dave's a good 'un, with many satisfied repeat customers.
Best,
Dan.
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Aberdeen.
Can I walk to you?
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Matt, your welcome at Dave's Bike Shed any time! Its a bit far from furry boots city tho ;D I do back onto the east coast mainline so if you were travelling south get off at Kirkcaldy or Inverkeithing and come along to me KY3 0XE.
I dont know the bike shops out your way but a quick search shows Holburn Cycles as an indie LBS albeit road biased, do you know them? You also have http://becycle.wordpress.com/ (http://becycle.wordpress.com/) who seem to rent workstands to the public and provide advice. My reckoning would be these people could be helpful to you. Why not visit without your bike and have a chat/coffee to sound them out?
Looking at your pictures your eccentric will be ok, at worst with it removed you could dremel off any edges that protrude. Tandems also use eccentrics for tension of chain between pilot and stoker and I have seen well abused ones, but a good mechanic can always have them retain tension; only in extreme cases would a new eccentric be required. Indeed I did a brace of bottom brackets in a tandem today - liking the aliteration!! eccentric was slightly ovalised in the bottom bracket shell but no worries all good again.
cheers
Dave
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EBB holding up well after x3 rides.
No chain slackness detected.
Just wondered what kind of strain is on the EBB to turn / change position, due to hard peddling?
Any thoughts?
Matt
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I think the strain on the EBB is not so small. Actually it must depend on where the EBB is positioned. I would think the worst spots are at extremes of its positioning, i.e. at 3 o'clock and 6 o'clock. In those positions, the entire force of your pedal downstroke becomes a torque twisting the EBB, because spindle is not centered over the bolts. Even at 12 o'clock, the intermediate position... your downstroke doesn't create torque directly, but the chain tension does. Seems like there ought to be a spot where the spindle is a bit toward the front, where the twisting from the crank just balances the twisting from the chain, and the EBB is just balanced on those screws. So probably there is a spot behind 12 o'clock where the twists add and those screws are really being tested.
Of course the spindle is only maybe 5 mm off center, so the torque is not so huge even when the forces are big. Still, I think the torque is big enough that e.g. tightening those screws to spec is worth the bother. I use a torque wrench there because it seems like a critical balance - I don't want to like push too hard and actually damage the EBB, but I want a nice dent that will hold.