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Broke my chain ...And the new one skips

alomacalomac Posts: 189
edited October 2010 in The workshop
(Update five posts down...)

'As the title says, today I broke my KMC Z-series 7 speed chain. I was literally just leaving my driveway, standing on the pedals to give it some extra shove in a 38:14 gear, but by no means grinding it.
It broke in two places: the quick-link, and at a pin eight links away. I haven't yet been able to find the quick-link (it's night here) so I don't know how it failed, but the other break looks like the outer plates opened up at one end and thus released the pin.

Is this just one of those things, or should I be looking for a cause? The whole bike is only 6 months old and has probably done less than 1000km. The chain has always been well maintained. I did open the quick-link on Friday for cleaning, but I've probably ridden another 60km since then with no problems. Should I be looking at the bike? Was I riding improperly?

Thanks for any input.

Posts

  • jeepiejeepie Posts: 495
    I had a very similar thing happen to me. I took the chain off to clean it. About a week later it snapped under very low pressure. Now I don't break the chain to clean it.... it's speculative but in my case I think I may have weakened the chain by breaking it or more likely not have fitted it back perfectly. As I get more experience I'm sure I'll pluck up the confidence to start breaking the chains again....
  • alomacalomac Posts: 189
    Because I had the quick-link, I didn't have to break the chain to clean it. I did break the chain to install the quick-link, but I don't thinks that's relavent since that was months ago and because the pins of the quick-link replace those removed with the breaker, I didn't have to worry about reinstalling them. The second point of failure was never broken.

    FWIW, I did install the correct quick-link (7 speed, KMC).
  • MichaelWMichaelW Posts: 2,226
    There are various types of easy-fit link.
    The original SRAM master link is totally re-usable and can fit on any chain of the correct width (ie 8spd/9spd). I prefer this type whatever the chain.
    The Taya type has 2 pins fixed onto one plate and you bend it it to fit the opposite plate. Note really re-usable.
  • sc999cssc999cs Posts: 596
    It's strange that it broke in two places. I would have expected one break at the weakest point, two breaks suggest that you had two weak points. Maybe the plate opening caused the tension of the chain to drop allowing the quick link to come loose? In which case it may have just been one of those things.

    I have broken a chain myself. I started off in similar circumstances and the chain just snapped. I suspect that it jumped a cog on the rear cassette and caught between the drop outs and cassette, jamming and then breaking. I'm guessing from the scratches on the frame but I'm still not really sure what happened.
    Steve C
  • alomacalomac Posts: 189
    UPDATE:

    I've since fitted a new chain (SRAM PC830) but now it skips/slips. I've tried looking for a stuck link, but can't seem to find one: the rear derailler cage does sometimes give a little twitch as I backpedal, but none of the links look obviously wrong as they roll off the jockey wheel. I took it in to the LBS but they found nothing wrong apart from a bent derailler hanger, and fixing that hasn't cured the problem. I'll take it back on Monday, I guess.

    The slipping tends to happen when I apply extra pressure on the pedals to give it boost uphill. It'll generally slip three or four times in rapid sucession. On the flats it's fine, even in the bike's highest gear, with only the occassional, seemingly random appearance.

    The entire bike has less than 2000km on it, so the cassette and rings are still good. One jockey wheel does have a worn bushing, but it still turns okay.
  • V5adeV5ade Posts: 192
    Could be a worn cassette (they tend to wear at the same rate as the chain for me),
    Somewhere in the Surrey Hills :-)
  • Sirius631Sirius631 Posts: 1,015
    38x14? Is it the inner of a double or the middle of a triple that you are on? Is that the smallest or next to smallest sprocket of a 7 speed block you are using? I suggest you might be riding with the chain line having too much lateral deflection. This will lever chain plates open faster and cause more wear than running with a more relaxed chain line. It also increases the friction within the drivetrain, thus wasting your energy.

    I'd keep the two largest sprockets for use with the inner chainring, and the smallest two for use with the outer chainring. You have enough cross-over of ratios between the inner and out chainrings, so you are not losing anything.
    To err is human, but to make a real balls up takes a super computer.
  • alomacalomac Posts: 189
    Yes, it was middle chainring of a triple, and the second-smallest cog of a 7-speed block. I was under the impression from a MTB book I have that you could use all cogs from the middle chainring, although their example used a 9-speed drivetrain.
  • jairajjairaj Posts: 3,009
    If the old chain and cassette are old they will have worn together so they match up. When you put a new chain on it is not worn and will not match your cassette fully so can skip a bit. sometimes the issue is not too bad and the new chain will bed in after a bit. have a read on sheldon browns web site for more info.
  • alomacalomac Posts: 189
    Thanks, but the cassette and original chain have less than 1200 miles on them, so wear shouldn't be an issue.
  • Hi Alomac,

    I have much the same problem on a Boardman Hybrid. My chain snapped and it caught in the rear derailleur snapping the rear hanger. I replaced the rear hanger myself and left it at the bike shop to fit a new chain.

    But now the chain slips when on the inside chainring (its a compact chainset) and either of the 2 smallest cogs on the cassette. After an inspection I noticed that the slip was actually caused by the chain rubbing on the outside chainring and this was lifting the chain up and causing the slipping. Maybe you have a similar issue - did you look closely for the chain rubbing or catching on the outer chainring as you spin the crank?

    Unfortunately I haven't been able to work out why this is happening - the derailleurs appear fine and I don't believe these are part of the issue as I can clearly see the lateral angle of the chain from the chainring to the last 2 cogs of the cassette is clearly causing the chainrub.

    Oddly these gears worked fine before the accident so i believe it should be possible to get them aligned again.

    I tried stripping the cassette and putting it back on to be sure this was spaced as before and this made no difference.

    Anyone got any suggestions? Could it be the chain? or the bottom bracket somehow out of line?
  • cyberknightcyberknight Posts: 1,238
    jairaj wrote:
    If the old chain and cassette are old they will have worn together so they match up. When you put a new chain on it is not worn and will not match your cassette fully so can skip a bit. sometimes the issue is not too bad and the new chain will bed in after a bit. have a read on sheldon browns web site for more info.

    +1

    Had a similar problem when i put a new chain on , it kept skipping and jumping, i had to put a new cassette on as well.
    I now have a chain wear tool and check regularly to see when the chain needs replacing.
    FCN 3/5/9
  • alomacalomac Posts: 189
    In my case, the cassette was worn. The reason the LBS gave for this happening so quickly was my propensity to take off from a standstill in 'high' gears (38:16, 38:18 ) and my size and long legs, which apparently give me a powerful stroke. I don't know, I used to be a bit of a masher, but not to the point of it being uncomfortable/strenuous, and I almost never get out of the saddle as I find doing so awkward.
    Anyway, the new cassette seems fine so far. They've put in a more road-oriented unit than the original (11-28T vs. 14-32T). I'll be checking my chain wear monthly now.
    Thanks and Cheers.
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