Chain drop issues problems resulting in bruised unit- Mtbr.com
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  1. #1
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    Chain drop issues problems resulting in bruised unit

    Frame 2010 superfly ss carbon

    rider 6'1" 148lbs

    Each of the last several rides as well as occasionally prior (totaling near 10) I have dropped my chain. While it was disconcerting I could not figure out why. It was just really annoying that under max power, especially over obstacle or turning that I could not trust my bike. Yesterday I ended up slamming my unit into the stem at full power going up a hill.

    Tension is fine and I have good hardware on there to eliminate any slider movement.

    I took it to the lbs and we messed with another wheel. I can get different chain tension just by shifting my weight on the bike no matter what wheel is on the rear. The guy riding behind me and the lbs think the frame is flexing and the chain pops off. I don't think there is any way I should be able to do that so I took it to the trek dealer. The dealer seems to blame the hub

    Is it likely a little play in the hub could be the issue? I'd rather build a wheel than pony up for a new bike. But I dont want to buy a wheel and the bike is the issue. I am also afraid to really try it out because I never know when its going to go.

    Any thoughts? Sorry for the long post

  2. #2
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  3. #3
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    Next two:
    CHAIN
    LINE

  4. #4
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    chain line was done using the method mapped out in the sticky... I'm not new to ss. If its off, it isnt by much.

    I can't imagine riding with a cup being much better

  5. #5
    Downcountry AF
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    what dropouts does your frame use 135 QR or 142 TA? What hub and axle combo are you using? What chain, chainring, and cog are you running? What size chainring and cog?

    you think it's slipping off the rear cog and not the front right? If your using a smaller cog 17t or under you would likely benefit from a larger rear cog. Another potential solution is a NW cog.

    I'm curious to hear what components your using, we'll go from there.
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  6. #6
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    easton xc one ss hub/rear wheel
    20t armada wide base steel cog (less than 400 miles)
    fsa dh 7000 series 32t chainring
    135 QR
    chain is kmc Z single speed chain

    anything I missed?

  7. #7
    Downcountry AF
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    the chain is dropping in the rear?

    I'm a little surprised to see your having this issue with a 20t cog and a SS chain (less play laterally). Assuming chainline is good, frame flex could be your problem. I'd inspect it closely for cracks if this is a relatively recent problem.

    The only other real weak point is the 135qr. A bolt on hub would be stiffer, but there's no guarantee that's going to solve your problem unless you can rule out all other possibilities. ya know?

    I think the quickest/easiest and cheapest potential solution is the NW rear cog.
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  8. #8
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    Dumb question, but did you buy the 1/8 or 3/32 KMC chain?

  9. #9
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    I agree frame flex or hub/cog lateral movement in the power stroke are likely candidates. It sounds like something is moving laterally that is causing the chain to pop off.

    Another idea, although much less likely, is that the crank spider or bolts are cracked or allowing lateral play at the chainring. This happened to me and was very hard to figure out until a piece of one of the spider arms actually broke off. My chain kept popping off randomly until I replaced the cranks.

  10. #10
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    I've used both 3/32 and 1/8, I don't remember which is on now and it's at the trek shop so i can't check. Dropped chain with both wodths though.

    I thought maybe there was an issue with the chainring or crank, but I have had that apart recently and didn't see anything unusual.

    You guys think a little play in the free hub (I mean very little play, just feels a little loose) could really be the issue? I know Ohmygato you are thinking lateral mvmt, but what we see is vertical, as if the BB is dropping and raising causing moments of high and very low tension.

    I don't want to sound like a weenie but I am pretty scared to hop on and ride like normal after that incident.

  11. #11
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    Quote Originally Posted by khardrunner14 View Post
    I know Ohmygato you are thinking lateral mvmt, but what we see is vertical, as if the BB is dropping and raising causing moments of high and very low tension.
    This sounds like the crank/chainring is off center or just has poor manufacturing spec. Most drivetrains have tight and slack spots, you just need to be aware of it and position the chainring so that it is minimized (assuming 104 bcd).

    Is the chain dropping in the front or rear??????
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  12. #12
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    Dropping from the rear.

    There are slight variations in chain tension from the position/shape of the chainring, but not much. Even at the most slack position I still have great tension unless I am putting in serious power.

  13. #13
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    I'm mystified. OP, no doubt you've already checked the chain for twisted links and the cog for bent teeth. Does the frame flex a lot when you hammer? If so, what else could it be? I can't imagine a hub with enough flex in it to drop a chain... gotta be the frame.
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  14. #14
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    yeah all teeth are good

    For some reason when hard core power is on that is when it goes bang

  15. #15
    Armature speller
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    Can you get the chain back on without removing the rear wheel?

  16. #16
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    barely

  17. #17
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    When the chain pops off does it always end up on one side of the cog (towards the frame or towards the hub)? Or is it randomly on either side? Do you recall if it coincides with only the right or left pedal stroke, or does it happen with either?

  18. #18
    Armature speller
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    Does it happen with different cogs?
    Under load, there's a lot less tension on the lower chain and you can get a side to side movement that can put a tooth outside one of the narrow chain plates and it'll peel the chain off. But the cog teeth have to be pretty narrow for that to happen.
    I've only had it on an Origin8 16t (really narrow) and never on the Surly 20-22 or King 18.

  19. #19
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    teeth are pretty wide and straight its an on-one armada cog. pretty beefy. It's happened with a surly cog as well, though maybe not as often.

    As far as I can remember it's right pedal stroke and falls to the outside about every time, toward the drop out.

  20. #20
    Ahhh the pain....
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    Not sure if others have mentioned this, but if your chain is worn, it will have much more lateral movement. I know some people use the typical chain checker, but I prefer to lay mine flat on the ground, and then keeping the sideplates vertical, make as tight of circle you can with it. If that circle is under around 23" in diameter, it's too worn.
    Now, I've had chains derail with 25 and 26" of diameters as measured above, but found that by adding a slight chamfer to my cogs, it was enough to help.
    I run a AB oval and those naturally have a slightly slacker point of the revolution. I've have found while the bike is in the stand, if I can apply force to the chain near the cog and easily get the chain to climb off the cog, then that's a problem.
    BTW, I do think some of the issue is flexibility of the frame; mine is a 2010 Ti Lynskey Ridgeline that is kinda known to be a bit noodly of a frame.

  21. #21
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    chain has maybe 350-400 miles and this has been at least an occasional issue since day 1, though it is getting worse

  22. #22
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    Quote Originally Posted by khardrunner14 View Post
    As far as I can remember it's right pedal stroke and falls to the outside about every time, toward the drop out.
    I suspect a combination of frame flex, very slightly off chainline, and chain wear are the culprits. I think you are slipping the chain off the right (dropout) side of the cog when you push hard on the pedal because you flex the frame inward and thus the cog gets angled in slightly where it should pick up the chain. But instead of picking it up it misses and throws it instead.

    I suggest you move the cog out toward the dropout ever so slightly, like definitely <1 mm. This is probably going to result in the chainline not looking perfect, but when you flex the frame in on a hard pedal stroke the cog will angle itself in so that it still picks up the chain. Also put on a new big boy 1/8" chain.

  23. #23
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    Quote Originally Posted by Raybum View Post
    I've have found while the bike is in the stand, if I can apply force to the chain near the cog and easily get the chain to climb off the cog, then that's a problem.
    I agree with this as a good basic test.

  24. #24
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    I cant get it off the cog while in the stand. It's tight.

    I see what youre saying about flex. Just seems excessive since I don't weigh much. I think the chain is 1/8.

  25. #25
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    Quote Originally Posted by khardrunner14 View Post
    I cant get it off the cog while in the stand. It's tight.

    I see what youre saying about flex. Just seems excessive since I don't weigh much. I think the chain is 1/8.
    You don't need to weigh much to flex a frame substantially. Even on an ultra stiff frame if I really stand on the pedal I can get the frame to visibly deflect. I'm only 155 lbs. and not very strong. If you combine that with the chainline being slightly off and the chain being worn out you can miss a link pretty easily and pop it off.

    The most important thing to notice when diagnosing is that it's repeatable - always toward the dropout and always with the right pedal stroke.

  26. #26
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    If chainline is correct, then there's not many culprits left.

    Is it a chain designed for derailleur use, ie designed to slide off the cogs easily? Or is it a single speed chain?

    Are your cogs and chainring proper SS items with proper teeth, ie not cut away to allow derailing? (NB a large skinny rear cog can flex if it is a stamped one)

    Long shot - check for cracks in chainstay near the BB.
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  27. #27
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    All SS specific drivetrain. None of the drivetrain is particularly worn. All less than 400 miles.

    Right now the bike is at the trek dealer for them to check it out. I will get it back possibly Friday. Depending what they find I will triple check chainline.

    To me it sounds like there is no way this is related to a little hub play. The only way I can see that being an issue is if the hub moves slightly while the frame is flexing causing the cog to not line up.

  28. #28
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    if it is a 1/8 chain on 3/32 rings i am gonna blame the chain (combined with flex of course). i have had this happen with too wide a chain. i also like the idea of moving the cog over ever so slightly to the side it is dropping on. finally, if it is always dropping at the cog, some cogs have deeper teeth (check out rennen for example)...

    i'd love to hear if you get it figured out!

  29. #29
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    It's dropped with both 3/32 and 1/8. Also dropped on diff cogs, allSS specific with deep teeth.

    I will def post back if I get anything figured out.

  30. #30
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    Update: Trek dealer says the frame is flexing normally, though my lbs is skeptical still. Trek guy thinks it is a combination of a worn chain, hub play, and flex that is causing the drops.

    I guess the plan is to get a wheel from my lbs and see if that makes a difference. The trek dealer stripped one of the brake rotor bolt holes using a drill to put the rotor back on, so now combined with the play in the hub and age of the wheel I won't sell the bike with that wheel on it. I am hoping a new wheel makes everthing ok (as well as a new chain).

    We will see what happens.

  31. #31
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    What the hell?! This is turning into a Trek nightmare story. Not that I have any better ideas for you at this point, but I wouldn't trust your Trek dealer anymore. He doesn't know what's causing the problem and he stripped one of your bolt holes on a rookie mistake. I hope he's giving you a brand new wheel for free. This is BS.

  32. #32
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    He charged me $21 for the privelege. He claimed the problem was there already. I don't shop there. My lbs is a pro mechanic and I try to do all my business there. He is going to order a rather cheap rear wheel for me soni can either ride (if thats the problem) or sell and move on.

  33. #33
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    Try a narrow/wide rear cog?
    Last edited by NordieBoy; 06-11-2017 at 07:02 PM.

  34. #34
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    Quote Originally Posted by khardrunner14 View Post
    He charged me $21 for the privelege. He claimed the problem was there already.
    What an ass. If nothing else I would inform Trek that they have an idiot dealer who doesn't know how to work on bicycles and who represents their illustrious brand poorly.

  35. #35
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    Quote Originally Posted by ohmygato View Post
    What an ass. If nothing else I would inform Trek that they have an idiot dealer who doesn't know how to work on bicycles and who represents their illustrious brand poorly.
    Easy with the tar and feathers. I recently bought a brand new triple crankset and when I removed the granny ring, one of the chain ring bolts galled the threads and stripped. Fortunately, I only paid $45 for the crank set, I'll sell the rings for $15 and it'll only be used for SS or 1x configs on my bikes, so no loss. But no amount of mechanical expertise would fix a scenario like that.

  36. #36
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    Quote Originally Posted by khardrunner14 View Post
    He charged me $21 for the privelege. He claimed the problem was there already. I don't shop there. My lbs is a pro mechanic and I try to do all my business there. He is going to order a rather cheap rear wheel for me soni can either ride (if thats the problem) or sell and move on.
    This is the point when you contact Trek directly.

  37. #37
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    Quote Originally Posted by mack_turtle View Post
    This is the point when you contact Trek directly.
    Trek told me to take it to these guys. They wouldn't do anything and said everything had to be handled through a trek shop.

  38. #38
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    Quote Originally Posted by khardrunner14 View Post
    Trek told me to take it to these guys. They wouldn't do anything and said everything had to be handled through a trek shop.
    This is the point where you buy your next bike from a reputable company.



    (sorry, I had to. I f%&@ing hate Trek)
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  39. #39
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    Try a King SS rear cog. 7 years of SS and I've never dropped the chain off the rear cog. Quality piece of machining.

    Good luck


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  40. #40
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    Quote Originally Posted by solo-x View Post
    Easy with the tar and feathers. I recently bought a brand new triple crankset and when I removed the granny ring, one of the chain ring bolts galled the threads and stripped. Fortunately, I only paid $45 for the crank set, I'll sell the rings for $15 and it'll only be used for SS or 1x configs on my bikes, so no loss. But no amount of mechanical expertise would fix a scenario like that.
    This has nothing to do with a dealer having no idea how to diagnose a problem on one of their bicycles and giving up on it, then subsequently damaging the customer's bicycle by using the wrong tool in an effort to save time.

  41. #41
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    Silly question, but did you verify that your cog is installed correctly? I have seen cases where you can flip the cog around and install it, but it seems some cogs are "dished" a little differently. Could effect the chain line... Just a thought

    Trying a new cog is an excellent idea. Currently, I run a surly cog. Kind of heavy but that thing is nuke proof. Had it on there for many years and never dropped a chain.

  42. #42
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    Quote Originally Posted by ohmygato View Post
    This has nothing to do with a dealer having no idea how to diagnose a problem on one of their bicycles and giving up on it, then subsequently damaging the customer's bicycle by using the wrong tool in an effort to save time.
    I guess I'm skeptical the Trek mechanic admitted to using a drill to install the rotor bolt. My money is that the bolt galled in the hole during removal is all I'm saying. Now, if the mechanic actually admitted to stripping it with a drill at install time, then yeah, tar and feather.

    Ps. I use an electric drill to install my rotor bolts all the time. I've yet to strip a bolt that way.

  43. #43
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    Quote Originally Posted by solo-x View Post
    Ps. I use an electric drill to install my rotor bolts all the time. I've yet to strip a bolt that way.
    There's nothing wrong with that so long as you start the bolts by hand and don't use a drill powerful enough to do damage.
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    Stop asking how much it weighs and just go ride it.

  44. #44
    EAT MORE GRIME
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    135 QR ? that has to be it. those are garbage for SS

    get rid of that baloney, there is no way you can make it tight enough

    I have always been able to f-up an SS ride with a QR...they suck if the dropout
    allows sliding

    go solid axle and 15mm bolts or 142 thru and crank that sucker tight with a persuader

  45. #45
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    I watched him install the rotor bolts, with a drill, standing right next to me. Then he said "oh man, that's weird" (somethibg to that effect as the bolt kept spinning but not getting tighter.

    I've had several cogs on in, they are installed properly and chainline was good as verified by 2 mechanics (one of which I really trust).

    Got a new rear wheel today but I am likely going to move on to something else.

  46. #46
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    new wheel on, stamped cheapo cog instead of the on-one, different chain, chainlain set perfectly, tension tight....

    going to try my luck. I mean, I don't want to have any more kids anyway so whats the worst that could happen?

  47. #47
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    after reading all this.
    It sounds like its the chain. I know you said its newish. I run a 9 speed chain on my SS.
    Or its the chainline

    I run a AB Oval 34T, a endless cog and a 9 speed chain on my SS and I have never had a chain drop. You can even move the chain around when the oval is on its loose rotation and still will not drop a chain.

    If the chain line is off just enough and you can flex the bike just enough the chain can come off.
    Too Many .

  48. #48
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    yeah apparently the chain was worn

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