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  1. #1
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    Timing chain derailment

    My wife and I have an Ellsworth Witness out here in Socal. Every once in a while (once every 5 rides) we would drop our timing chain. Usually this would occur on steep, tight switchbacks. My theory was, that as I am negotiating the switchback I probably pause in my pedaling without letting my wife (stoker) know and that causes just enough slack to let the chain ride over a couple teeth. So, please understand I, as the captain, accept full responsibility. I think that frame flex may contribute to it as well...possibly.

    I recently needed to replace my timing chainrings and decided to get a couple RaceFace narrow/wide toothed chainrings and give them a go. They are made primarily for 1X and single speed set ups to prevent chain drop. A simple description is that the tooth width, on the chainring, alternates to fit the natural wide/narrow pattern of the chain.

    Well, after about 10 rides I'm very impressed and have yet to drop a timing chain. Another added benefit is that the normal chain "hum" from the timing side is now too quiet to notice.

    Am I simply being more diligent and pedaling properly? Or, are these new rings making up for my shortcomings? I'm really not sure, but I thought I would pass this on regardless.
    Attached Thumbnails Attached Thumbnails Timing chain derailment-image.jpg  

    Timing chain derailment-image.jpg  

    Last edited by jeepr84; 06-10-2014 at 07:03 PM.

  2. #2
    PMK
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    Full tooth profile is best. Not a guarantee but less likely to derail.

    PK
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  3. #3
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    Nothing but respect for your experience and contributions to tandem MTB, but the smallest (narrow) tooth on this chainring is equivalent to standard RaceFace chain ring and the wide ring is much wider. The height of all the teeth are identical. It's just that every other tooth is wider than normal. How is that less than "full tooth" profile? I am absolutely not trying to be argumentative just simply want to understand your statement.

  4. #4
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    Thinking maybe he's saying that having teeth that match the width of the chain will be less likely to to derail, IOW, the wide/narrow you're using is a fuller profile than using a regular chainring.

    Of course, that's not technically the tooth profile, but who cares? You fixed it!

  5. #5
    PMK
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    Nope, wrong direction guys. I am not talking tooth width, but rather profile if traced onto paper. Some people I have seen use middle chainrings with some teeth lower than others for better shifting. I have not run chainrings with different thickness on the teeth for timing rings. They should work fine and seem to work well for you.

    Sometimes lesser quality rings will have runout and run up / down causing tight spots followed by loose spots.

    Others run timing chains too tight and some drooping loose.

    Typically though, a decent quality chainring, with full tooth profile and a chain tension just slight loose of tight works real well.

    I won't say any one brand of chainrings is better. We have run various brands. Currently we have Salsa stainless but I plan to go back to the thicker aluminum rings for added stiffness when they hit stuff.

    As mentioned, excellent it is fixed and working well.

    PK
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  6. #6
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    Any information on other Witness teams dropping the sync chain? I've never experienced that on our ECdM, and did only once on our Burley road tandem, but that was due to an inadequately-tightened BB.

    If other Witness teams have had the same, then it may well be a flex issue, especially since everyone's likely running different drivetrain parts. If not, it may just have been a question of the quality of your old sync rings. Did you have a big difference in chain tension during a full revolution?

  7. #7
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    Some of the derailment issues are consistent across virtually all tandem brands. I suspect the common factor would be unequal pedaling force between captain and stoker at the same time the frame is being flexed by a maneuver or other factor. We've dropped timing chains on both Ventanas and Fandangos at the same spot on the local trail, and it's a short steep uphill pitch with a turn over a root in the middle of it. I explained to my stoker that the unequal power to the cranks in that situation contributed to it, and that I would back off a bit while she pushed a bit harder. It worked.
    It won't cure every chain derailment problem, certainly, but I think there's something to unequal force on the pedals during maneuvers.
    Middleburn says they're making wide/narrow UNOs soon, so that might be an option for tandems with those cranks.
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  8. #8
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    Quote Originally Posted by TandemNut View Post
    Some of the derailment issues are consistent across virtually all tandem brands. I suspect the common factor would be unequal pedaling force between captain and stoker at the same time the frame is being flexed by a maneuver or other factor. We've dropped timing chains on both Ventanas and Fandangos at the same spot on the local trail, and it's a short steep uphill pitch with a turn over a root in the middle of it. I explained to my stoker that the unequal power to the cranks in that situation contributed to it, and that I would back off a bit while she pushed a bit harder. It worked.
    It won't cure every chain derailment problem, certainly, but I think there's something to unequal force on the pedals during maneuvers.
    Middleburn says they're making wide/narrow UNOs soon, so that might be an option for tandems with those cranks.
    I think you are spot on with this. Our crux was a steep sharp swithcback out here on one of our local trails. Like I said in my original post, I do think it has to do with unequal pedaling force. With that said, so far the narrow/wide tooth pattern has seemed to prevent any derailments...I'm keeping my fingers crossed. I would have to think if people are having success with these on 1x9 (or 10) set ups with no chain retention devices and standard derailleurs...it has to help, at least a little, on a tandem timing chain. I would be excited to hear of anyone else trying these and whether or not they have similar results.
    Last edited by jeepr84; 06-14-2014 at 11:19 AM.

  9. #9
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    quote: nutterAlex "....I explained to my stoker..." Brave lad you are Alex, brave lad... I try NEVER to "explain" NUTT'n to MY stoker!

    Dropped our timing chain again this morning. Just ordered a set of narrow/wide rings. We'll see if that fixes it.

    The big debate was color ;/ but also went from a 38 to a 32T. Haven't really worked out why, but it just seems like it would be better... got an on-going argument in my head over the pros and cons and it's driving me nuts. Going wilderness canoeing for a week, so that ought to settle it.

  10. #10
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    32T gives more clearance for obstacles, but more chain wear.

    RE: dropping the sync chain - I guess we're just not riding hard enough!

  11. #11
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    I have only dropped a timing chain once. The loss was due to the position of the eccentric bottom bracket. When looking at the eccentric bb from the left side of the bike the bb should be set to proper tension between 11:45 and 9:30 so that any rotation of the bb can only tighten the chain and not loosen it. With proper tension and this orientation it should be quite difficult to loose that chain without breaking it. Perhaps my opinion shouldn't count for much since my t-chain is on the drive side which probably negates any frame flex issues.
    Attached Thumbnails Attached Thumbnails Timing chain derailment-drive-train-sm.jpg  

    Last edited by DHMASTER; 07-12-2014 at 11:19 AM.
    DW-DHR,VPX,SLX,SX,Stump Jumper ht.,Specialist, Bicycle Fabrications DH Tandem,Gravity Bike,Bamboo 29rs,Profile Uni,Renovo R4.

  12. #12
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    Quote Originally Posted by Okayfine View Post
    ...I guess we're just not riding hard enough!
    lol

  13. #13
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    Narrow Wide

    I like it, we ride faster now

    Something I hadn't anticipated, it is much easier to get the pedals synced now as the chain moves in 2 link increments, making differences more obvious.

    Solid as a rock, clearly engages more positively. The smaller size and the heftier construction seems to be much stiffer and stronger as well.


    Timing chain derailment-timing-ring.jpg

  14. #14
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    Our first mountain tandem was a ~ 1990 Santana Rio. We had frequent problems with dropping the timing chain. After some experimentation and observation I determined that the cause was frame (bottom tube) flex when I would really stomp on the captain's crank to power up a short steep hill, etc. The fix was a combination of running the timing chain as tight as reasonably possible AND moving the chain rings to the INSIDE of the cranks. This reduced the leverage of the chain pull on the bottom bracket axle that is trying to bend/flex the bottom tube.

    We later TOTALLY eliminated the problem when we changed cranks by getting the shortest possible bottom bracket axles and having the least possible axle amount sticking out on the timing chain side. The chain was thus MUCH closer to the bottom tube greatly reducing the bending leverage.

    Another factor is the size of the timing chain rings. We always run the smallest practical chain rings because it increases clearance of log crossings, etc. However this maximizes the tension on the chain (and thus the bending force on the bottom tube). On or current ECDM we are using cranks that accept a granny gear on the timing side and are using 28T granny sprockets which maximize ground clearance AND minimize bending leverage on the bottom tube. This has been bulletproof.
    Last edited by Sam Jones; 07-21-2014 at 12:12 PM.

  15. #15
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    I've not checked the price difference between a standard chain ring and a narrow/wide one, but theoretically, having a wider tooth profile should reduce the tooth wear making the NW ring more economical in the longer term.....................or is all the drive loaded onto the narrow tooth?

  16. #16
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    Tooth profile at the chain contact edge on a NW ring is same width on the thick teeth as the narrow teeth. eg:


  17. #17
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    It looks like some of the drive will go onto the links as well as the roller after a bit of wear (wide tooth).

  18. #18
    PMK
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    Quote Originally Posted by DHMASTER View Post
    I have only dropped a timing chain once. The loss was due to the position of the eccentric bottom bracket. When looking at the eccentric bb from the left side of the bike the bb should be set to proper tension between 11:45 and 9:30 so that any rotation of the bb can only tighten the chain and not loosen it. With proper tension and this orientation it should be quite difficult to loose that chain without breaking it. Perhaps my opinion shouldn't count for much since my t-chain is on the drive side which probably negates any frame flex issues.
    You have sweet custom bike. I suspect the builder ensured stiffness when selecting the bottom tube. Same side or opposite side drive could be insignificant on your machine.

    As for the clock angles you posted, are you using 11:45 to indicate just prior to spindle at highest point and 9:30 to indicate just above centerline for the spindle on the aft side.

    I ask based on since you run single side drive, is it possible your clock angle are veiwed from the left side where you probably make your adjustments. For us, I setup our eccentrics to adjust from the right side to avoid the timing ring.

    I, whenever possible run the spindle above the eccentric horizontal center line and position it between 1:00 and 3:00.as viewed from the right side.

    Confessing though, since the timing stuff on our Co-Motion road tandem has some 9000 miles and required removing a link during a road trip event, I have been too lazy to replace the entire setup even with spares on hand. That bike eccentric is positioned between the 9:00 and 12:00 position as viewed from the right side.

    Both setup work fine on their respective bikes and riding. Both bikes run the better design Bushnell type.

    PK
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  19. #19
    PMK
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    Quote Originally Posted by Sam Jones View Post
    We later TOTALLY eliminated the problem when we changed cranks by getting the shortest possible bottom bracket axles and having the least possible axle amount sticking out on the timing chain side. The chain was thus MUCH closer to the bottom tube greatly reducing the bending leverage.
    The fantasy design... A frame that has protection for the timing rings by using the concept of running the timing chain down the bikes centerline and allowing the bottom tube to protect it. The cranks would be all 3 of a non drive style, however the BB would require the ability to hub the timing rings. Timing chain tension would be via a two pinch bolt per side setup with individual cups left and right.

    A double bottom tube setup would be easier and stiffer.

    PK
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  20. #20
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    Well, 25 rides into this experiment (15 since my original post) and we have yet to drop a chain. This even included a race where I seriously blew a couple of shifts and we hit numerous switchbacks under full power...our previous Achilles heel. I am definitely a believer.

    I am stoked that others have given this a try and look forward to other long term reports.
    Attached Thumbnails Attached Thumbnails Timing chain derailment-image.jpg  


  21. #21
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    I read this thread with interest, but didn't really take it all in until now. Today we rode our local singletrack, faster then we've been able to do before. At one point we had a chap follow us as he'd not seen 'anything like that before'. My stoker was putting the power on, and on a section very similar to the one described by Alex
    and it's a short steep uphill pitch with a turn over a root in the middle of it
    we shipped the timing chain.

    Looking at it now we're back at base, I think the eccentric could do with a bit more tension, and that's certainly the first thing I'll be doing. But a set of Middleburn narrow wide rings could be tempting.

  22. #22
    MTB Tandem Nut
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    Middleburn is now shipping thick/thin chainrings in 4 bolt 104 bcd pattern. We'll have them in stock in the next few days in hardcoat. The UNO T/T's are coming within a month or so.
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  23. #23
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    Tightened the Eccentric today - quite a lot of slack there. We're off to the Morvan tomorrow for two weeks, so we'll see what happens there, then perhaps upgrade when we get back.

    Thanks for the info Alex. Matt from Middleburn visits the shop where my son works here in the UK quite often, as there are about 20 miles apart. I'll be asking him to source them I'm afraid...it's a bit more convenient :-)

  24. #24
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    Most of you folks on this board have forgotten more about off-road tandems than I ever knew so I humbly ask: Why would unequal pedaling between captain and stocker have anything to do with timing chain derailment?

    I'd think the timing chain doesn't even "know" how hard the stoker is pedaling but rather only "knows" how hard the captain is pedaling (and thus putting stress on the chain and boob tube)?

    Obviously the captain would have to pedal harder (thus more boob tube flex) the less the stoker was pushing on any given hill/speed so maybe you mean this "indirectly" leads to harder captain pedaling and thus more flex???

  25. #25
    PMK
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    Sam Jones, please check your pm's for an unrelated question about motorcycles.

    PK
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