Conference noted::bicycle

    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

    
    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

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

      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)
    

RE: <<< Note 2947.4 by SHRCTR::VINCENT >>>

To follow up about my situation, all of the things listed were OK on my bike.

I'm curious about how wide the front derailleur cage is on various makes of
derailleurs. Mine is a cheap Shimano model which came with the bike nine years
ago. It is not marked as to model number; I'm sure it's not RX100 or anything
above that. The cage on this unit is about twice the width of the chains I've
had, which are all relatively inexpensive hyperglide-compatible chains of one
sort or another -- nothing especially narrow (I have a six-speed rear drive-
chain). With my custom modification (i.e., bend!), it's now perhaps 1� times
the width of the chain (at the extreme front of the cage).
						-- Tom

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

    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

    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.  
    
                                      

    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.
    
      
    
    
    

    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

    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.