Skipping chain (and old chains)

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Skipping chain (and old chains)

Postby simonn » Thu Apr 24, 2008 10:50 am

My new (well, S/H) OCR-2 has an SRAM 9 Speed 12-26 cassette (no other info than that).

On the work stand (I have yet to ride the bike properly) the chain skips the second largest sprocket (23?) in both directions. It did this with the old chain and also the new chain (same make and model) I put on this morning. I was told that the chain definitely needed replacing by the bike's former owner, so thought I would give that a shot first to see if it solved the problem. The old chain was quite stretched, it is always nice when you watch maintenance videos and, well, they work.

Adjusting the cable tension has not fixed the problem. It either shifts into the second largest ok but then skips some others, or skips the second largest and changes smoothly for the others. Do I need to really fine tune this?

The teeth look ok, or at least in the same condition as the other sprockets (to my untrained eye).

Ideas anyone?

Would it be okay to ride for the time being if I avoid that sprocket, i.e. could it damage the new chain (something I really want to avoid)?

Also, it there any reason at all to keep an old chain or should I just chuck it?

I am a noob and about as handy as no-hands freddy, so, please, be gentle.
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by BNA » Thu Apr 24, 2008 11:16 am

BNA
 

Postby Jean » Thu Apr 24, 2008 11:16 am

In the process of doing what they do the sprockets of cassettes and chains become interdependent - that is the wear on both essentially matches each other. You can replace just the chain if you catch it early enough (by measuring the 'stretch' - generally with a specific gauge), but the general view is that you'll only get two chains to one cassette.

If they've been running together for too long you'll have to replace both chain and cassette.
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Postby simonn » Thu Apr 24, 2008 11:27 am

Jean wrote:In the process of doing what they do the sprockets of cassettes and chains become interdependent - that is the wear on both essentially matches each other.


But that does not explain the fact that the symptoms are the same for the old and the new chain.
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Postby leximack » Thu Apr 24, 2008 11:29 am

just a bit more info to help Simon out, i was the previous owner so know the history.
This si the original chain on the bike and original cassette. I have a park tools chain wear checker and it has reached its wear limit. It was like this for approx 3-4months but only done about 300km after it had reached the limit, i used my commuter as my main bike since end of Jan.
I believe the cassette is OK (no expert though) and probably just needs tuning. But having said that cassettes are super cheap so may aswell get one now and be done with it, then tune them together.

Don
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Postby MJF » Thu Apr 24, 2008 11:33 am

Not quite true - the pitch on the chain changes with wear, but the pitch on the cassette stays the same, just the wear rate shoots up as the load is concentrated on less teeth as the chain stretches.

Simonn - your problem sounds like the derailleur cable & outers needs lubing or replacing, or the derailleur itself is worn. Take it to your LBS and get them to check the outers to start with - a lot of the cheap ones come apart causing the cables to stick. I've had to replace the outers for my front deraillerur because of this problem, and I've had a similar problem to yours with the rear which was fixed by trimming the end of the outer cables and lubricating.
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Postby Kalgrm » Thu Apr 24, 2008 11:34 am

When you say "skips the second largest sprocket", you are saying it doesn't stop on that gear, right? It will either move to the (say) 20t gear or the 26t gear, but never stay on the 23t gear?

If that's the case, it's your tuning of the system that's failing, not a faulty cassette. MJF could be on the right track too.

Cheers,
Graeme
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Postby simonn » Thu Apr 24, 2008 11:53 am

Kalgrm wrote:When you say "skips the second largest sprocket", you are saying it doesn't stop on that gear, right? It will either move to the (say) 20t gear or the 26t gear, but never stay on the 23t gear?


Spot on. It sometimes stays on 23t, but with "the chain doesn't want to be on here" grating sound. This is on the work-stand so no load. I imagine it would jump in this case under load.

MJF wrote:Take it to your LBS


But I want to do it myself! :D:cry:

The day after I bought the bike, I was taking my MTB to my LBS to fix a couple of broken spokes and mentioned that my new bike would need a new chain. They immediately said that they would have to change the cassette as well, despite what Don had said (<rant>I am always suspicious of this kind of stuff. I used to scuba dive *a lot* and the dive industry is the worst for "upgrade repairs" and the reality is that money is not the issue, it is being made to feel like a mug!</rant>). This is basically why I decided to try and learn how to fix my bikes myself.

What would you expect to pay LBS for this?

Thanks for the help everyone.
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Postby leximack » Thu Apr 24, 2008 12:00 pm

general bike service with no parts needed is about $50
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Postby MJF » Fri Apr 25, 2008 8:06 pm

simonn wrote:
Kalgrm wrote:When you say "skips the second largest sprocket", you are saying it doesn't stop on that gear, right? It will either move to the (say) 20t gear or the 26t gear, but never stay on the 23t gear?


Spot on. It sometimes stays on 23t, but with "the chain doesn't want to be on here" grating sound. This is on the work-stand so no load. I imagine it would jump in this case under load.


I was never able to get mine to work on the road after the LBS had it on the stand. Careful alignment on the stand followed by small tweaks on the road should get you there.

BUT - as it works in most gears but not some, we are back to a sticking cable issue or a problem with the dérailleur.

simonn wrote:
MJF wrote:Take it to your LBS


But I want to do it myself! :D:cry:


I know how you feel... but the tools start to get expensive. With my front dérailleur, the cable outer (which rather than the old spiral wind stuff is made from hi-tensile wires) had come apart and I had a number of strands 4cm into the shift mechanism. Took me ages to cut through those strands of wire with side cutters so I could get it to the LBS to replace the outers... but they have those nice cable cutters for just this purpose.

Tell you what - put it into top gear, push the derailleur towards the wheel to get some slack and then pull a cable end off the frame, then pull all the outers so you can see if they need trimming or replacing. If they look O.K., check the cable for any wear, grease and assembly is the reverse of disassembly. Worst case if you FUBAR it is you will need to take it down to the LBS and say "I'd finish it myself, but I'm really busy at the moment...".
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