I replaced the chain recently - the new chain unships violently when I apply a moderate amount of torque, such as when setting off standing. As in, it comes off the big ring to the outside (i.e. away from the small ring). If I set off seated in the saddle pedalling very gently it's ok, but if I accelerate, it comes off. Similar to this, Chain slips off biggest cog under torque, but in my case the 'and then it's back to normal' doesn't manifest itself - the chain actually comes right off outboard of the largest chainring. Notes:
- Have recently regreased bottom bracket, but is now back on correctly and no significant play
- Old chain was at (or maybe past) the 1% stretch mark before I took it off
- Chainline looks no worse than it was before
- Chainset is an Ultegra R8700 34/50
- Have checked the front mech is definitely not touching the chain (so it's not that that's throwing it off)
The chain appears to be meshing correctly on the chainring in the bike stand, it's just when I apply torque that it violently unships, which is obviously unacceptable from a safety perspective if nothing else.
The chainring looks quite worn, see below (it hasn't been changed in the 5 years I've had the bike)..... and the only thing I can think is that the old chainring wore along with the chain, and the fact I let the old chain get past 1% stretch has affected the chainring to the point where it can no longer support a new chain.
Nothing else has really changed. Yes, I took the bottom bracket off to regrease it, but have put it back on - as far as I can tell - correctly, and thus should operate just as well as it did before.
Will replacing the chainring fix the problem, or is this a symptom of a deeper malaise / different problem?