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  1. #1
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    Timing Chain Question

    My wife and I ride a Co-Motion Speedster. We just came back from a 1 month tour and during that time I did break the drive train chain. I was wondering when I should consider replacing the timing chain? Also is it common to also replace the left side chain rings at the same time?

  2. #2
    Senior Member Clarabelle's Avatar
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    I'm no expert, but I think it has more to do with chain wear than time. Sheldon Brown's web site has a section on chains that describes how to assess wear:
    http://sheldonbrown.com/chains.html

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    Timing chains will stretch and will need to be replaced due to that. You need to measure the chain for stretch and replace when needed. Again Sheldon Brown's site is a good one to look at. I replace The chains on both side at the same time. There is alot of force being applied to the chains on a tandem so they do wear out faster than on a single. I could stretch the life of the timing chain more that the other side but to me I would rather replace both chains at the same time since if I do break a chain there is another person that will be annoyed other than me, and it is harder to get a tandem back yo your vehicle than a single.
    Comotion Speedster, Caad 9, Salsa Vaya, Lynskey R230

  4. #4
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    We had to replace our timing chain (TC) this past spring. I think that this was the first TC replacement; definitely no more than two. We ride 1500-2000 miles/year
    (we're closing in out 10k on our Speedster). I've basically gone with idea that so long as the eccentric can keep the slack out, I'm good. With this past replacement, our LBS ended up using two "normal" HG chains. The leftover will be used to supplement the our next timing chain replacement.
    Jeff

    Learn from other people's mistakes. You won't live long enough to make them all yourself.

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  5. #5
    Senior Member diabloridr's Avatar
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    Timing chain wear will usually be much slower than the drive chain because (1) timing chain sees force from Captain only, drive chain handles force both from Captain and Stoker, (2) drive chain sees lateral forces during gear shifts which accelerate wear, while timing chain does not, and (3) drive chain is interfacing with ring teeth much more often than the timing chain.

    Drive chain wear will manifest itself as poor shifting performance, while timing chain wear will eventually severely wear the timing rings.

    We probably go through 3 or 4 drive chains before we do a timing chain replacement (We use a Park gauge to assess chain wear). YMMV.

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    Thanks for all the replies! I will keep good records and wait on the replacement.

  7. #7
    PMK
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    Quote Originally Posted by diabloridr View Post
    Timing chain wear will usually be much slower than the drive chain because (1) timing chain sees force from Captain only, drive chain handles force both from Captain and Stoker, (2) drive chain sees lateral forces during gear shifts which accelerate wear, while timing chain does not, and (3) drive chain is interfacing with ring teeth much more often than the timing chain.

    Drive chain wear will manifest itself as poor shifting performance, while timing chain wear will eventually severely wear the timing rings.

    We probably go through 3 or 4 drive chains before we do a timing chain replacement (We use a Park gauge to assess chain wear). YMMV.
    Agree, and the radius of the bending is much different comparing a 44t or similar timing ring set to wrapping around some of the smaller cassette sprockets.

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  8. #8
    Senior Member zonatandem's Avatar
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    Timing chains can easily go at least 4 times longer than drivechains.
    Not as fussy, as you can adjust eccentric to take up any chain stretch.
    Some folks actually use 'old' drivechains for crossover chains.
    Another school of thought is to replace one third of crossover chain with new chain. Repeat as needed.
    Just our input.

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    I thought it wasn't the actual slack in the timing chain due to stretch that was the problem, but the fact that only one tooth at a time was being pulled by the teeth of the timing rings as a result.
    How does tightening the chain via the eccentric change anything other than prevent a possible derailment?

  10. #10
    Nigel nfmisso's Avatar
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    And as the teeth wear on the timing chain sprockets, you can swap them front to rear; because the teeth wear on opposite sides - OR turn them around inside to outside.
    Nigel
    Mechanical Design Engineer

  11. #11
    Senior Member zonatandem's Avatar
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    Keeping the crossover chain properly tensioned will avoid you dropping that chain.
    And yes, you can swap out the crossover chainrings as stated above.

  12. #12
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    If one is handy with tools, can take a bit of aluminum place and make a little C shaped tool with the tips of the C that will just slip snuggly into a new chain but be sloppy loose on any chain that has stretched very much... just an idea. Don't know if there is a retail one made

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