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  1. #1
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    Bonking ... not feelin' well Chain skipping mystery on new build (not a newbie)

    Got a chainskipping mystery. Can anyone give me an idea or two?

    This is my 4th build of a single speed. Got a nice steel lugged road frame (Marinoni) from 1986 ( emailed Marinoni with the serial number).
    - new cog (Surly wide base 16 tooth)
    - new chain (Sram PC68). No stiff links.
    - new ring 42 T
    - cranks are used Campy Mirage, in good shape, spins true
    - new rear wheel, built by LBS experienced wheel builder, spins true
    - no bent teeth on cog or ring
    - frame is straight, rear derailleur hanger is not bent.
    - Chain line is perfect (by measurement and straightedge and eyeball)
    - used road derailleur as a tensioner. Shimano 600.

    Chain skips on the cog under hard pedalling (watched it happen repeatedly), almost with each downstroke. Doesn't skip with light pedal presure. Chain doesn't skip or catch when on the bike stand>

    Could the used derailleur be the problem? Seems to be in good shape, cleaned it up and greased the rollers.

    Is Surley cog compatible with Sram PC68?

  2. #2
    "Its All Good"
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    Could well be the compatibility of the chain with the Surly cog..

    Just the other day, for a trial, I whipped the wheels of Momentus's SS. He is running a Niner rear cog, I run a 991 hollowpin chain. Exactly the same problem as you mention, was a big no go, could not ride it at all....

    I would check that first, the chain was more or less sticking to the cog and not releasing, doesnt sound like yours is as bad....

    Best of luck, not cool to have this after building a new stead...
    The_Lecht_Rocks: whafe - cheeers - may i offer an official apology for the wagon wheeler "dis-belief"

  3. #3
    CB2
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    The chain and cog should be compatible.
    I'd check your derailleur. Your pulleys could be too worn; I've had this cause skipping before. Also check the b tension screw and make sure the pulleys aren't riding up on the cog.

  4. #4
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    Quote Originally Posted by CB2
    The chain and cog should be compatible.
    I'd check your derailleur. Your pulleys could be too worn; I've had this cause skipping before. Also check the b tension screw and make sure the pulleys aren't riding up on the cog.
    I adjusted the b tension, no effect. I have the drailleur set up with a short peice of cable - the head in the barrel adjust and the end clamped to the derailleur. This allows a fine adjustment of the cage position relative to the cog, by turning the barrel adjuster. No effect from that either.

  5. #5
    one chain loop
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  6. #6
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    "Wide Surly" Could the cog be made for a 1/8 chain instead of the 3/32?
    You do have vertical drops, right?
    Is the chain short enough?

  7. #7
    Schipperkes are cool.
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    This is my setup on my Ti Fat Chance; worn cog & chain ring, 7spd chain, alloy Control Tech pulleys on a 600 rear derailleur. Never had the chain skip nor come off.

    Make sure that the hanger is aligned!
    Quote Originally Posted by mikesee
    Better suited to non-aggressive 125# gals named Russell.

  8. #8
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    Quote Originally Posted by banks

    This is my setup on my Ti Fat Chance; worn cog & chain ring, 7spd chain, alloy Control Tech pulleys on a 600 rear derailleur. Never had the chain skip nor come off.

    Make sure that the hanger is aligned!
    Hanger is aligned. I don't have the cage pulled out as straight as in your pictur. Mine is more vertical. Would pulling the cage tight help things? Never been an issue on other biulds where I have used a derailleur as a tensioner. I do have a nice XT long cage derailleur.

  9. #9
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    Quote Originally Posted by hu-man
    Hanger is aligned. I don't have the cage pulled out as straight as in your pictur. Mine is more vertical. Would pulling the cage tight help things? Never been an issue on other biulds where I have used a derailleur as a tensioner. I do have a nice XT long cage derailleur.
    Short cage would be better for this application, and yes, if your D is fairly vertical you do not have enough tension on the chain.

  10. #10
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    Surly seems to be a bit picky with chains. I used an old model surly cog with rounded teeth on top, the new ones have flatted teeth, similar to chris king. It made a new KMC K710 skip, as well as a shimano 8speed chain.

    This was an 18t. This was using a regular frame with a 9 speed rear hub, chainline near perfect and using a normal derailer so the chaingrab on the cog was as good as it could get and definately better than when using a singlespeed frame without chaintensioner. My mate had the same issues with his 16t surly and a KHE chain.

    The surly measured rather big in diametre compared to a shimano DX cog and a singlestar cog, the surly was almost 1 mm larger than the other 2.

    Asking around, people mentioned that other cogs of other brands also had a larger diametre than what an 18t cog should have, according to the shimano technical drawings and the diametre of an 18t steel singlestar cog, which is probably the best steel cog ever made. However, none of them exceeded the indicated diametre more than the Surly cog did.

    When I used the surly with an older stretched shimano 8 speed chain it performed flawlessly. Even still today, I still don't know what caused this skipping. It could be the teeth design or the diametre that is/was too big or something else that caused incompatibility between chain and cog. Eventually a lot of people had no issues at all with this cog whereas others faced the same problems as I did.

    Surly changed the design of their cogs by using a different tooth shape. I haven't tried those however so I don't know if they are an improvement or not.

  11. #11
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    It sounds like it's a tension issue. Just take a few links out of your chain and you should be good to go. The PC68 is a great SS chain (assuming you have a 3/32 cog). And it sounds like everything else is kosher. The issue is almost certainly excess chainlength. Get it as short as possible (without binding).

  12. #12
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    I would allso try a different coq. I had a DMR ss 16t coq that would not work on any chain (ss, 8 speed or 2 different 9 speeds). It skipped when pedaling uphil or hard accelerating. I took a 16t coq from a XT casette and have had no problems since.

  13. #13
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    If your tensioner/derailleur is nearly vertical, then your chain is probably only grabbing 4-5 teeth on a 16 tooth cog. With the amount of tension being applied to the chain with the 42 tooth ring there just isn't enough chain grabbing the cog to prevent skipping. Take some links out like the guy above said, and set it up like the pic above, so your chain is wrapped around the cog as much as possible. The more teeth your chain grabs, the less the chance of skipping. Its why surly recommends using their tensioner to push the chain up, instead of pulling it down. It grabs more teeth that way.

  14. #14
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    you should use a dmr 16T single speed cog with a standard shimano or in your case sram chain and then your ride should be perfect and also look at the gusset squire ss tensioner

  15. #15
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    Mystery 99.5% solved. Derailleur hanger was twisted out of alignment horizontally(harder to see than being bent in or out vertically) and I shortened the chain. The chain still does the occasional infrequent 'skip' as if the chain has risen away from the cog then fallen back into place. I am thinking this will go away as the new components "wear into" a fit with each other.

  16. #16
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    Have you tried a different cog? I'm guessing you have poorly machined cog if it's still skipping at all.

  17. #17
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    Quote Originally Posted by hu-man
    Mystery 99.5% solved. Derailleur hanger was twisted out of alignment horizontally(harder to see than being bent in or out vertically) and I shortened the chain. The chain still does the occasional infrequent 'skip' as if the chain has risen away from the cog then fallen back into place. I am thinking this will go away as the new components "wear into" a fit with each other.
    Straighten the hanger if you haven't already (adjustable wrench will do the trick) and pick up a 1/8" chain, the extra play between it and the 3/32 cog should set you right.
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  18. #18
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    Had the same problem, hu-man. Took as much slack out of the chain as possible, worked like a charm as well. The random skip also happened with mine, just takes time. Good luck.

  19. #19
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    also, make sure the cassette lockring is tightened all the way

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