I'll add to Mark's comment by saying that you should be certain that your chainrings are true. If they aren't, a rubber mallet, a prybar and some patience may be needed to eliminate the runout. Also, if the crank or ring is particularly flimsy, problems may continue even once the rings are straight. It is also not beyond the realm of possibilities that your BB is out of square, placing the ring oblique to the desired chainline.
Mark Bulgier <mark@bulgier.net> wrote:
Paul Aslanides writes about his front derailment problem:
> You've most likely hit the nail on the head.
> The rear derailleur is out of alignment, just a little.
> >
> > From: "Paul Aslanides"
> > > Hi All,
> > > I've just rebuilt my recently-acquired Claud Butler,
> > > 'Electron' Super Five model. It's a lovely, smooth ride, too.
> > > The problem is that when I change gear, the chain also
> > > derails off the chainwheel, almost every time.
It is this mechanic's opinion that derailing in front is a problem exclusively in the top of the chain (tight side), and is not affected by what happens on the loose side where the rear derailleur lives. Especially since you say the misalignment is slight, you should keep looking for the cause. A more slippery chain lube (do you use grease or wax by any chance?), different chain maybe, or a chainring with taller teeth might help, but I doubt it'll ever be completely free of the problem.
I find rear-derailleur-only bikes often derail in front, and so I don't like them much unless they have cyclocross-style plates on either side of the chainring, or a front derailleur screwed down to stay in one place (a "railer" since it doesn't derail?)
I know some will post their disagreement ("Mine *never* derails"), but I have seen way too many that did derail at least once, in a couple of cases probably causing an athlete to place second in a time-trial he or she would have won. Usually the stakes aren't so high, but there's still the slight chance it could be dangerous, and at the least, the grimy job of putting it back on. (Yes I know some ways are neater than others, but it's never exactly fun is it?) The "railer" doesn't have much downside except perhaps aesthetically. I understand if you prefer to keep the bike original though.
Good luck, and let us know if you fix it
Mark Bulgier Seattle, Wa USA _______________________________________________
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