Originally Posted by
cmcanulty
It is not front der as it shifts fine but if I shift to large chainring, then shift down to rear cogs smallest or 2nd smallest it immediately throws chain off large chainring and off crankset entirely. The front der doesn't move at all when this happens and appears to be correctly aligned. Will check the frame issue today.
Given that the bike has been transported and that the fault happens when the chain is angled by moving to a smaller cog, then it may be that the large chain ring is bent causing the chain to be thrown off. When the chin is more or less in line, then it remains on the ring. Look directly down on the ring from above while rotating the pedals. You should then see a wobble if it is off true.