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Old 01-26-06, 12:45 PM   #1
comradehoser
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10-spd chain falling off

the situation: brand-new jamis nova, compact 105 10-speed, truvativ cranks and chainrings (alu, I think).

On the outside (big) chain-ring, when in the outside (small) gears, the chain falls off to the outside under load. the chain then loops around itself and takes out the front derailleur if I let it. Inexplicably, the f.derr. is not rubbing/overshifting that I can see. chainring bolts are tight.

The bike has a giga-x pipe bottom bracket whose crankbolt wasn't tightened down all the way when the f. derr. was calibrated. I took it back to the LBS to be readjusted when the crank-arm fell off on the way to work, so everything should be fresh and snug.

I don't get it. Chain too tight, maybe?
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Old 01-27-06, 06:40 AM   #2
Bobby Lex
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I'm assuming this happens when you are shifting to the big ring from the small ring? Sounds like your outer-limit screw on the front derailleur needs to be re-adjusted. The Park tool web site will walk you through the process.

Bob
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Old 01-27-06, 07:34 AM   #3
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Quote:
Originally Posted by Bobby Lex
I'm assuming this happens when you are shifting to the big ring from the small ring? Sounds like your outer-limit screw on the front derailleur needs to be re-adjusted. The Park tool web site will walk you through the process.

Bob

Here's the link Bob is referring to:

http://www.parktool.com/repair/readhowto.asp?id=75
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Old 01-27-06, 09:24 AM   #4
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thanks,

actually, no. the chain is already firmly ensconced on the big chain ring, and I'll be pedalling along quite happily until it randomly falls off, generally when I'm putting it under some load.
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Old 01-27-06, 09:36 AM   #5
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If the crank arm was loose and you rode it for any amount of time "until it fell off", chances are the crank arm hole that fits on the axle was rounded out a bit and probably will never seat perfectly or completely. Hence, there's that ever so small amount of play and when you put pressure on the right point (probably on the down stroke of the drive side) you shift/wiggle the crank just enough to make the chain not line up with the teeth of the chainring. If it was the bike shop that didn't tighten down the crank arm before giving it to you, they probably owe you a new crank arm as there's no way to make yours fit tightly again like it's supposed to.
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Old 01-27-06, 09:40 AM   #6
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+1 for the outter limit being set too far out...you really have to get it damn close when in the big ring and small cog combo. Also be sure your FD is aligned properly.
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Old 01-27-06, 01:10 PM   #7
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Also under load (esp if you are standing up on the pedals), your bike frame is flexing, which will make your FD move from where it is when your bike is unloaded. Like Grasschopper said, adjust the front derailleur outer stop. It might also be worthwhile to make sure that there's no play in your crank arms/bb, and that the chainring/crank spins very true. Although wobble is unlikely, it would certainly be exacerbated under load.
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Old 01-27-06, 04:14 PM   #8
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check for cracks in the front chainring.
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Old 02-23-06, 11:09 AM   #9
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sorry to drag this old horse up, but this is really driving me crazy, and the problem isn't getting any better, even after I took it in.

I've taken the Jamis back to the LBS to get the warranty tune with attention to the front derr. problems, so all the stops *should* be okay, they look and feel to be okay to me. Besides, I can trim the front derr, so rub is not the issue, I don't think. The chain is not rubbing when it falls off. There is no side-to-side play in the cranks. Keep in mind this is an external bearing set that mounts on a pipe running through the BB shell, so if I understand correctly, it should be plenty stiff and solid--do you think the crank bolt issue would still apply? (not sure I'm understanding what to look for--deformed crank bolt or BB face?)

The chain falls off in the same place every time--when the drive-side pedal reaches 2 or 3 o'clock under load, and when the chain is in the 12t, 13t, or 14t rear cog. It falls off and proceeds to wrap around my pedal axle and/or snarl sideways in the chainrings. there is also some specific wear on the side of 2 or 3 teeth on the chain ring (easy to see, the ring is anodized black). If the crank is at 3:00, they are at 5:30. My untrained eye doesn't see any cracks, or any bent teeth/warpage.

I should also add when shifting from the 50t to the 36t, the chain often does not engage the smaller ring and rides along in the space between the chainrings.

WHAT is happening? I am getting SO frustrated with geared bikes. I wanted to spend some cash to upgrade from my disintegrating and forever-fixing alum. MTB commuter so that my commuter would be MORE reliable, but I'm having so many more problems with this bike. I really want to love it, but I'm starting to regret my purchase. Is it that the front drive is not compatible with the shimano 105 10-spd chain? I need to fix this if the LBS can't/won't, as this is my primary commuter and the problem has led to several unpleasant situations (sudden loss of power in an uphill intersection as light is turning--not good).

Should I expect to have to pay for chainring repair/replacement, or is this something that would fall under faulty parts/warranty?

here are the drive train specs in more detail:

truvativ elita compact 50/36 front, truvativ giga-x pipe bottom bracket, truvativ elita cranks, shimano 105 28.6 mm. band-clamp front derailleur, 105 rear derailleur and shim. 5600 chain.
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Old 02-23-06, 11:16 AM   #10
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forgot to mention, I found a bunch of ultegra chainrings from a 9-speed triple by happenstance, but I don't know if they would be compatible with a 10-spd compact.
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Old 02-23-06, 04:53 PM   #11
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I would take it back to the LBS and tell them that you need it fixed. It sounds like it's creating a dangerous situation.

Was the LBS able to duplicate the problem during their shakedown run, after they tuned it up for you?

If you're not already dealing with the manager/owner of the LBS, then you need to talk to him/her. If you're already dealing with the manager/owner of the LBS, then you need to have them provide you with the contact info for the Jamis rep.
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Old 02-23-06, 05:12 PM   #12
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The fact that the FD does not bring the chain all the way over to the small chain ring makes me think that the limit screws are still out of adjustment. It sounds like the wrench has the low speed too tight & the high speed limit too loose. We all get a little dyslexic at times and it may be happening here. Check it out yourself on that Park Tool website noted by NoRacer above.
No one should go thru this aggravation for this long.
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Old 03-22-06, 02:31 PM   #13
comradehoser
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After diagnosis and evaluation by the LBS wrencher, I thought I would bring anybody who cares up to speed on the true cause of the above-mentioned ailments:

drive train incompatibilities.

The Truvativ compact crankset on the Nova was billed as 9/10 speed compatible, but as I found out, was not in fact compatible with the 105 10 spd gruppo. I don't know exactly what was incompatible--perhaps some of the spacing and ramping in the chainrings, as the chain consistently fell off at a specific spot in the pedal cycle. Both Truvativ and Jamis apparently were aware of the issue prior to the shop getting in touch with them; Truvativ is sending a replacement crankset, but I will have to wait *another* 1-2 months. Crazy that I got this bike in Jan. and have only ridden it maybe 10 times.

I didn't think that mixing/matching component sets would make that much of a difference, but I guess when you are dealing with the smaller tolerances of the 10-speed world, little things matter.

I'm appreciating my beater fixie more and more.
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