Cannondale SI BB30 Compact - chain keeps falling off

[intern]

Also a long shot... Perhaps the chain has a slight lateral bend in it?

Thanks - checked that and changed the chain because it was bent from being thrown off and caught by the next pedal stroke. New chain...same prob.

[intern]

It needed to be asked anyway

Ok so if the limit screws are correct then it is very strange. Do you have another crank you cant test with it?

Going to be an interesting one to follow.

Luckily I have a fellow hubber handy who has a spare set of cranks for me to try...

[intern]

Maybe a long shot.....check orientation of RD and if it is straight. Had a similar problem on MTB.......saw that there was rotarional torque on the chain that contributed to it climbing of the big blade (2x10) at the front. Problem was due to bent hanger.....replaced hanger......running smooth again.

 

Does not make sense, but the gremlin seems to have fanished......

This is an interesting one which I have not considered. Thanks - going to check that out..

[intern]

Check the facing of the frame bb? If not square the whole bb, crank etc will be skew causing the crank to rotate offline and the chain to go over as the chainring rotates out to in.

Also an interesting suggestion. I've test ridden the bike (bit small for me) and the cranks don't feel off centre (that's something you can pick up by feel quite readily) but will have it checked. Thanks!

[T-Bob]

Does sound like an odd problem. I have a spare one of those crank sets if you need to test. With like for like.

[intern]

So I've tried a different chainring, same problem. Changed the hanger, same problem. Going to try changing the rear derailleur next and see what happens then....