Chain reaction

[Matt2matt2002]

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

[Danneaux]

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.

[geocycle]

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.

[Matt2matt2002]

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

[geocycle]

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.

[Andre Jute]

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.

[Danneaux]

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.

[Matt2matt2002]

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)

[Danneaux]

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#msg30297

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?

<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)

[Matt2matt2002]

Thanks Dan, and as you can see, being 60 makes you do things twice when you,think you've done them once!

Matt

[Danneaux]

 

All the best,

Dan. (...who fixed it for you)

[julk]

Matt,
**HAPPY BIRTHDAY**

just think of yourself as two 30 year olds
Julian.

[Matt2matt2002]

Matt,
**HAPPY BIRTHDAY**

just think of yourself as two 30 year olds
Julian.

 
Thanks Julian. We have the same sense of humour.

[Matt2matt2002]

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

[Danneaux]

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.