Originally Posted by
rushibhai
cyccommute, I don't mean to hijack this thread, but what's the remedy when:
Going from middle to largest chainring on a triple (Ultegra FD, 105 RD long cage, 11-25 9 speed cassette, Tiagra shifters, many miles on everything), while on the smallest (fastest) cog in the rear, the chain comes off the ring to the outside, pedaling freezes up. I don't think the adjustment is the problem: I've checked all the stop screws and they look okay, things shift perfectly fine when on the stand. Happens when I'm cranking hard and shifting forcefully.
The crankset is pretty old and I suspect biggest chainring is a bit warped (though visually it still looks okay).
This is a limit screw problem. The derailer is moving the chain too far outboard and knocking the chain off the crank.
Park Tools will help you adjust it. The key to proper adjustment is to adjust the outer limit screw so that it won't rub but not so far outboard so that the chain can be knocked off.
It is possible to get the chain back on without stopping for this kind of problem. Click the front derailer back one step (towards the inside) while pedaling - lightly - and the chain can reengage. It takes a little finesse but you can do it with practice. However fix the problem
