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Conference noted::bicycle

Title: Bicycling
Notice:Bicycling for Fun
Moderator:JAMIN::WASSER
Created:Mon Apr 14 1986
Last Modified:Fri Jun 06 1997
Last Successful Update:Fri Jun 06 1997
Number of topics:3214
Total number of notes:31946

2947.0. "Help! chain's dropping" by SWAM2::BURDICK_JI () Sat Apr 29 1995 03:54

    I am having a chain dropping problem.  A lot of shifts (20%?)from the large
    to small chainring while in the second smallest cog cause the chain to
    drop onto the bottom bracket.  The chain also just rides the gears
    without engaging pretty frequently.
    
    It's Ultegra STI, 39/53, 13-23. KMC HP70S chain.  Specialized EPIC. 
    I've tried adjusting screws and changing the height and angle of the
    front derailleur.  Before I break down and take to the shop (a little
    pride at stake here - I'm trying to build the bike myself), I thought
    I'd seek the wisdom of those in the conference.
    
    Am I doing something wrong on the setup, or is it just considered bad
    practice to shift STI from big to small chainring while in the second
    cog?
    
    Thanks for the help.
    
    Jim
T.RTitleUserPersonal
Name
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2947.1New chain?ROCKS::ROBINSONTwitching the night away...Mon May 01 1995 11:295
    Not clear whether you have all new components (you mention "building
    the bike"), but if not, it sounds like you need a new chain or worn
    rings.
    
    Chris
2947.2Good shape ?JGO::GERRITSENMon May 01 1995 12:516
    
    Same as 2947.1; Look if all components are in good shape. If you have a 
    new chain it could be the point where you fit the chain togheter, maybe
    it doesn't bent enough at that point. Hope you understand what I mean.
    
    Ray
2947.3My Solution: Bend Derailleur CageLHOTSE::DAHLMon May 01 1995 13:1918
I have had this problem with my bike all along. Sometimes I could get the front
derailleur adjusted just right such that I could slam the front shifter from
big to small ring and the chain would not drop off inside. Most of the time,
however, I did not have it adjusted this well and so had to downshift the front
somewhat tentatively; even then I would occasionally drop the chain.

My solution was to bend the front derailleur cage. I've thought all along that
the cage was rather wide. When adjusted such that the outside plate moved
inward enough on downshifts to push the chain over onto the small ring, the
inside plate was well inboard, enough to allow the chain to sneek between the
small ring and the inside plate, resulting in a dropped chain. So I bent the
front-most portion of the inside plate outward (toward the outside plate),
narrowing the derailleur cage substantially. This has virtually (though not
entirely) eliminated dropped chains. One downside is that front shifts are a
little noisier now, since the chain rubs against part of an edge of the inside
plate rather than along the parallel (to the chain) face of the plate. I can
live with that; much preferred to a dropped chain (which I hate). 
						-- Tom
2947.4Some things to check....SHRCTR::VINCENTMon May 01 1995 16:4111
      You should be able to get it to shift ok without having to "bend" 
    anything, provided nothing has been tweaked already....
    
    *  Check the bottom bracket and make sure there is no play in it.  
    *  Make sure the derailluer height is correct.
    *  Check, re-check the adjustment screws.
    *  Make sure the derailluer is lined up correctly (no "toe-in/out")
    *  If the BB has an adjustable chainline, make sure that is correct.
       (also check to see if the BB spindel is in correctly - 1 side is
        longer than the other)
    
2947.5LHOTSE::DAHLMon May 01 1995 17:3313
2947.6UHUH::LUCIAMy other car is a CannondaleTue May 02 1995 19:1210
My brand-new Cannondale R600 dropped the chain 16 times in the first 70 miles. 
After many adjustments (by the shop), they gave up and replaced the small (39)
chainring and the chain.  The original was a DID Supershift and they put on a
Shimano.  This is with RX100/105 components.  The new 39 chainring was a
machined one (specialized) replacing the stamped one.  The first time I shifted
it fell off and has not since (400 miles of no troubles).  Even when I try to
drop it, it won't go.

Wierd.
Tim
2947.7Further thoughtsROCKS::ROBINSONTwitching the night away...Wed May 03 1995 13:348
    Still waiting to get clarification from base noter, but some further
    thoughts I've had since writing .1
    I think the clue might be in the "chain also just rides the gears". If
    this is happening, I still think that a worn chain is most likely, but 
    also chain tension or chain length (too many links) could cause this 
    problem. 
    
    Chris
2947.8thanks for all of the help so farSWAM2::BURDICK_JIWed May 03 1995 16:2910
    Sorry for taking so long to reply, I was on a business trip. The chain,
    chainrings, Bottom bracket, and cranks are all new.  The rear cogs have
    maybe 1000 miles on them, but they're working fine.  The chain was
    sized based on having just enough links to go around the big chainring
    and largest cog.  I  will look into the chain tension today, and
    recheck BB alignment and everything based on your ideas.  
    
    Thanks for all of the suggestions so far.  
    
                                      
2947.9Problem was wrong BBSWAM2::BURDICK_JIThu May 04 1995 21:4614
    Well,  
    I followed everyone's advice, and checked things over.  The chain was a
    little loose, but 2 more hours fiddling with adjustments didn't get
    rid of the problem.  So, I went to a shop nearby, and it turns out the
    other shop put in the wrong bottom bracket - 3mm too long.  The
    mechanic swapped it out and readjusted the shifting for $10 - quite a
    deal.  It was the chain line after all.
    
    Thanks again to everyone who responded.
    
      
    
    
    
2947.10MIMS::OLSEN_RFri May 05 1995 19:1211
    Another .02 worth...both my brother and myself has ultegra sti
    cannondales, you should see the scars in my chain stay from runnning
    the stock 39/53. We both swapped the 39 to a 42 and adusted the rear
    cogs to have a 23/13 or 23/12 and since going to 42 it had NEVER missed
    a shift. Some days I'd like to have the 39 so I could run a 12-21 but
    screwing around with the chain falling off all the time wasn't worth
    it.
    
    Good luck.
    
    Ron
2947.11SWAM2::BURDICK_JIFri May 05 1995 19:375
    I'll keep that option in mind if trouble starts occuring again. I wne
    with a 39 for the hills around here, but I'd rather have clean
    shifting.