Loose chain

[Matt2matt2002]

Hi folks.
I ride a Raven, 2 years old, third owner.
Best bike I have ever ridden.
Recently rode from Inverness to Fort William on the Friday and did return trip on the Sunday.
Raven was a dream to ride  and even coped well with a bit of off road stuff when given wrong directions.
Used front Ortliebs on the rear. Stayed in Youth Hostel. Met some marvellous folk and marshalled a mountain bike ride around the foot of Ben Nevis.

I have asked in the past about the apparent slackness of my chain and folk have advised to leave well alone.
I was tempted to tweak the bottom bracket but held off adjustment.
Sorry, no pictures since camera was lost a few months ago.
If you search some of the pictures I have posted under, Matts Old Bird, you may see the chain situation.

It is not so slack as to touch the rear stay but getting that way.
No jumping of gears and runs sweet.

However, coming home from work tonight the chain skipped off the cogs as I went over a small curb. By the time I had stopped to investigate, the chain was off front and rear cogs. Not sure which one jumped first.

Managed to sort things out and arrived home, slightly shaken. I thought I had bust the chain when I felt it go!

Suggestions please folks. Is it time to turn the bottom bracket a touch? '
(Advice on direction of turn please)
Should I contemplate removing a link?
If so, I have an original German chain with no easy link to remove.

Many thanks folks

Matt

[Planet X]

Chain stretch? Maybe time to replace it with a new one?

[Matt2matt2002]

Chain stretch? Maybe time to replace it with a new one?

Yes, no problem with dong that. Just wondered about adjusting the bottom bracket to take up the slack?
I have heard it should not be rotated so that there is a thin part against another part? Or something like that.

Matt

[jags]

wait until you get advice matt it might just need a turn on the bb.i reckon our man Dan will be along shortly to advise.

[Matt2matt2002]

wait until you get advice matt it might just need a turn on the bb.i reckon our man Dan will be along shortly to advise.

I can already hear the distant rumble of the Schwalbes.
 

[geocycle]

Yes, time to adjust EBB if the chain is falling off.  Chain stretch is not a big problem on hub gears but you do eventually have to take up the slack.  I tighten the chain fully then let it slacken slightly. I just use the finger method but the handbook has some measurements as to how much play you need.   It's important not to run it too tight that it damages the rolhoff.  Tightening is really straightforward, go for it!

[Matt2matt2002]

Yes, time to adjust EBB if the chain is falling off.  Chain stretch is not a big problem on hub gears but you do eventually have to take up the slack.  I tighten the chain fully then let it slacken slightly. I just use the finger method but the handbook has some measurements as to how much play you need.   It's important not to run it too tight that it damages the rolhoff.  Tightening is really straightforward, go for it!

Thanks. I'll give it a go at the weekend

[JimK]

yeah the main thing is to rotate the EBB so the spindle is going up away from the ground and toward the saddle. This keeps the thick part of the EBB down by the screws that push into it to hold it in place.

You want to tighten it so there is maybe just an inch of play, roughly. Turn the cranks and make sure there is no rumbling of bearings, that it's smooth.

Another thing to watch for - you don't want the indents on the EBB to start running into each other because then the screws can't hold the EBB in place properly. What I do is to take one screw out all the way so I can look down the hole and see what indents are already there. If there is an indent pretty close, with just a bit extra slack, then I will reuse that. I position the existing indent right under the hole and then tighten down the other screw, which should land right on the corresponding indent on that side of the EBB. Finger tight is good enough to keep things in place. Then I put in the other screw finger tight, check that the slack is reasonable, then tighten down to 10 Nm or so.

If there is not an indent where I need it, then I position the EBB to make sure that no existing indent is very close and then tighten the other screw pretty hard to lock the EBB in place then put in the screw I took out and tighten that. You just want the indents to be cleanly separated and not to run into each other to make a groove.

[Danneaux]

i reckon our man Dan will be along shortly to advise...I can already hear the distant rumble of the Schwalbes.

Whew! Matt, I was out of town for much of today, at my dentist's located in the state capitol of Salem, getting a new crown fitted to one of my lower-rear molars. Her practice is the best, so when she relocated from my hometown, I followed. Well worth it for top-quality service and makes a nice little journey three times a year -- occasionally by bike (260km round trip).

Matt, you've already received some really good advice: Time to reduce the slack and you can go about it by...
a) tightening the EBB (provided the chain hasn't stretched beyond what can be taken up
b) shortening the existing chain *and* adjusting the EBB
...or...
c) replace the chain.

You now know what "too loose" is, and may be wondering what would be "too tight".

I was in a similar position when I changed my 38T chainring for a 36T. I removed some links and reset the EBB, but then carefully read and re-read Thorn's instructions and worried about what constituted a too-tight chain. You can see how things played out in this thread:
http://www.thorncycles.co.uk/forums/index.php?topic=5569.0

Matt, be sure to pay particular attention to the discussion of tight spots in that thread. Not all chainrings and drivetrain components are perfectly concentric ("round" or "centered), so the chain can bind at places if you get things too tight and that is To Be Avoided.

I minimized the tight spot, then *at mid-span with the chain at its minimal remaining very small  tight spot*, I ended up setting my eccentric to allow 12.7mm/0.5in of chain slack, as I have successfully done with my tandem timing chain and EBB over many years of use.

This seemed a good compromise for my used chain with little wear/stretch. I feel sure I could have gone as tight as 10mm with no problem (but no tighter!), and indeed this is what a number of makers of Rohloff-equipped bikes recommend for proper tightness. I've been pleased with the 12.5mm and things hum along nicely with no binding or excess tightness even when standing on a climb with a full touring load.

As mentioned in the above link, Thorn's recommended measurement procedure goes into the intricacies of adjustment and how to measure the result: http://www.thorncycles.co.uk/thornpdf/ThornBikeOwnerManual2Web.pdf )

Congratulations on the Fort William trip, Matt; it sounds like a wonderful tour, and it is hard to imagine a better bike for it.

By the way, did you happen to see my PM to you on 16August re: your rusty stem bolt?

Hope this helps. If you run into problems, don't hesitate to give a shout and any of us will be glad to weigh in with suggestions.

Best,

Dan.

[Matt2matt2002]

Many thanks for all the advice on this topic.
This afternoon I up-ended the Raven, grabbed a 15mm and got to work.
Chain was indeed very slack, almost touching the rear frame stay.
I also noticed that both bolts were easy to undo with my fingers!
Surely not good?

I do not have the correct tool from Thorn for shifting the bracket but managed to turn it and reduce the chain tension. I re tighten the bolts and then felt the tension.
Too tight! So slackened off, made sure the bracket was centred and retightened both bolts.
Checked there was no grinding noise and pressed down on the mid part of the chain and was happy with the small amount of slack.
Also looked down and happy with the chain lining up fore and aft with cogs.

Out for a short spin and all appeared in order.

May I ask for clarification on the comments regarding, existing indents?
I didn't see any. Should I have seen them by looking down the holes after the bolts were removed?
May I have caused some future damage by not lining them up?

Apart from that all appears well.
But please see my next topic post on wheel noise. Nothing serious. More curious than anything else.

The Fort Wiilam to Inverness trip is to be highly recommended. I did the North side and South side.
North side was busier but I was riding on a Sunday so traffic only slightly crazy.
South side is slower on the Great Glen Way.
Please PM me is anyone needs more details.

Matt

[geocycle]

Many thanks for all the advice on this topic.
This afternoon I up-ended the Raven, grabbed a 15mm and got to work.
Chain was indeed very slack, almost touching the rear frame stay.
I also noticed that both bolts were easy to undo with my fingers!
Surely not good?

I do not have the correct tool from Thorn for shifting the bracket but managed to turn it and reduce the chain tension. I re tighten the bolts and then felt the tension.
Too tight! So slackened off, made sure the bracket was centred and retightened both bolts.
Checked there was no grinding noise and pressed down on the mid part of the chain and was happy with the small amount of slack.
Also looked down and happy with the chain lining up fore and aft with cogs.

Out for a short spin and all appeared in order.

May I ask for clarification on the comments regarding, existing indents?
I didn't see any. Should I have seen them by looking down the holes after the bolts were removed?
May I have caused some future damage by not lining them up?

Apart from that all appears well.
But please see my next topic post on wheel noise. Nothing serious. More curious than anything else.

The Fort Wiilam to Inverness trip is to be highly recommended. I did the North side and South side.
North side was busier but I was riding on a Sunday so traffic only slightly crazy.
South side is slower on the Great Glen Way.
Please PM me is anyone needs more details.

Matt

You can probably  see the indents if you move the EBB right to one side and in good light if you peer down the holes. But the best advice is just not to adjust so regularly that they can coalesce. Keep the screws nice and tight. 

Interesting comment from dan about the asymmetry of some chain rings. I experienced this with my recent surly ring but the thorn rings have always been pretty accurate.

[George Hetrick]

Interesting comment from dan about the asymmetry of some chain rings. I experienced this with my recent surly ring but the thorn rings have always been pretty accurate.

I replaced my original 42T Thorn ring with a 38T Surly, and also noticed the tight spot. I'm planning on replacing it with something else in a 38T, but don't know what. Surly's QC could evidently use some improvement.

[Danneaux]

Interesting comment from dan about the asymmetry of some chain rings. I experienced this with my recent surly ring but the thorn rings have always been pretty accurate.

Hi Geo' and George!

I've found Thorn's chainrings to be very accurate, and the Surly wasn't bad in my own experience. The concentricity problems in my case (I've found it to some degree on every bike I've owned over the last 35 years) seem to be the result of error aggregation across all the drivetrain components.

The BB cups themselves can be threaded slightly out of plane even if the frame's BB shell is faced, the spindle can be forged a little off or the square tapers might not be so very square, and the right crankarm can be not-quite-straight as well. If everything goes the wrong direction at once, I've found radial runout can exceed 1.5mm. This used to be a problem for me back in the day when SunTour called for 1mm clearance between the lower edge of their front derailleurs and the top of the large chainring.

I've found it helpful to approach the problem a sub-component at a time. If the shell is faced, there's not much to be done about the BB except to try another. Next, I test-fit the bare right arm on each of the four tapers, clocking it round the faces and measing the axial runout to find the position with least error. Then, I mount the outer chainring (the only one that matters in an IGH installation, though  check 'em all on a derailleur drivetrain) and again clock it 'round the mounting points. If you have indexed front gearing, then this can be problematic, as the 'ring may have ramps and pins that need to be mounted only one way if the indexing is to be correct; not a problem with plain 'rings. In my worst example, I went from 1.5mm of axial runout to .027mm just by rotating mounting points to get the least runout. .027mm is just about perfect...or perfect enough to no longer be an issue with the recommended amount of chain slack. A lot of runout can make a difference in measurement and I am convinced the resulting cyclic loading is a factor in overall chain life.

Rotating that Surly chainring on its mounts might just bring it into "round" again, guys. It did for me.

It's worth noting all may not be perfect at the back of the bike, either. Cogs can be lathe turned and accurate in each dimension...then threaded off-center or slightly crooked, which effectively causes a variation in runout even for IGH hubs and cogs. Cassettes and freewheels can be really bad due to the amount of play at the mounting surfaces, but it doesn't matter as much 'cos the rear derailleur cage's spring tension takes up the difference.

All the best,

Dan. (...who stores his derailleur bikes with the mech springs relaxed while parked and believes it makes a difference in preserving spring tension over the years)

[George Hetrick]

I replaced my original 42T Thorn ring with a 38T Surly, and also noticed the tight spot. I'm planning on replacing it with something else in a 38T, but don't know what. Surly's QC could evidently use some improvement.

I went to work on my bike today, and found the issue. While the steel Surly single ring has the same BCD as the Thorn crankset, the shoulder height is different -- there's about a 1.5mm difference between the actual inner diameter of the Surly chainring and the shoulder of the crankset. So, when it was installed, it wound up off-center. I've recentered it for the moment, but I'll need to replace it with a more appropriate chainring. Thorn is no longer listing teh ring on their website, so I'll probably just go Shimano, or something.

[Danneaux]

...there's about a 1.5mm difference between the actual inner diameter of the Surly chainring and the shoulder of the crankset.

Wow! That's a lot, George, and troubling. Hmm. D'you mean when the chainring is mounted on the arms, there's a 1.5mm gap between the inner edge of the 'ring and the crank spider's mounting flanges?

Just curious: Will or does the 'ring center on the chainring bolts? Or does it sort of rattle around on the sleeve nuts/bolts? Does your 'ring mount to the outer or the middle (inner) position on your crank?

My 36T Surly 'ring was a 104BCD for a 4-arm Deore crank and fit well, so there may be some difference if yours is a 110BCD for a 5-arm crank.

It might be worth dropping a note to Surly to see if you got a bad example. I've found them pretty responsive to inquiries.

Best,

Dan.