Bought this bike new a few years ago and recently upgraded to 10speed. Bike has thrown chain over the big ring twice now when shifting the cassette to the smallest cog at high speed and load. The first time there was a momentary seizure and my cranks stopped for a second but it freed and I just used my toe to correct and kept going. That is only incident that I can recall that may have caused this.

Yesterday, it threw the chain again under the same conditions. I was already in the big ring and when going into small cog on the rear, the chain went off on the outboard side. I figured I just needed to make some more adjustment but when I got home, the FD looked weird to me.

FD and large ring is original 9sp SORA double. Chain and rear cassette is 10sp. SORA shifters were replaced with SRAM Rival.

I guess I should put a new 10sp FD on there or might pinch it back and ride it as is. Has anyone bent an FD cage like that?

Number400, I just checked my double chain set bikes and both FDs, RX100 and 600, have a purpose made bend near the tail of the FD's cage to move it inward. The Sora may just gradually bend the whole cage, but it would be best to compare with a known good Sora double FD.

Depending on how close the chain set is to the seat tube, chainstay length and other possible factors the off set from the larger chain ring to the smallest cassette cog can be enough to derail the chain. I'd first suspect a laterally stiff chain or the chain is not flexible laterally at some point along it's run. Shimano chains assembled with their special pins can be very stiff at the joined links.

Brad

New Part? It's engineering .. flat FD cages are now in the past. back when 10 was 5 by 2..
and the hand skills were what made it shift .

Tried rotating the FD around the seat tube? or bought a chain minder, so it catches the chain wanting to come off on the inside?

While I agree that flat, unshaped, cages are behind us my first thought was that this cage may have been "worked with" by a mechanic during the tuning process. Subtle reshaping to control chain movement or rub is pretty common by many wrenches, done well by those who have been around a while.

But your description suggests another possibility. That the first chain derailment might have caused the cage to bend to allow the chain to fit between the cage and the ring. I would check the gap of the outer cage plate as it is above the big ring teeth. 2-3mm is the usual. Also the outer cage plate is usually roughly straight , not bowed.

Front der adjustment and manipulation is far less cut and dried then rear shifting is. If the cage is distorted having some one who has done this stuff many times before might be the better suggestion than a less experienced wrench bending the cage here and there how many number of times...

I'll add, although not asked about, that shifting under power will produce waves of tension and displacement in the chain. This is why when young we were taught to shift under minimal pedal pressure. Andy.