Brompton chain jam

[woollypigs]

Peli's little Brompton is a 6 geared version with the Kinetics 8 gear upgrade/conversion. She is reporting that sometime when she folds/unfolds the chain falls off. Also when she is cycling the chain jams and then jumps off. Some folding and unfolding and very dirty fingers later she manage to fit the the chain back.

I'm about to give it a poke and go "hmmmm" and "aaaahh I see" and certainly have a PingFeck-NoDon'tEatThatYouSillyMutt-It or two! I had a ride on it a few weeks back and found no problems with the gears when I twiddled with the Gripshift.

Could the panel shed some light and share some ideas what I need to look out for, it is not often a Brompton comes my way as bicycle repair man, so therefore don't really know where I should squirt some WD40 and say that should do it.

[Kim]

Firstly, is the chain length correct...

[Gattopardo]

Check the tensioner spring is clean and travels properly, had an issue with a tensioner on my single speed that did a similar thing.

[woollypigs]

Gave it a good all poke. The only thing I noticed was that when you went from 5 to 4 or 4 to 5 along with 4 to 3 or 3 to 4 the gears didn't engage correctly, quite a lot of jumping about the chain did. Some some fettling/indexing about I got that to behave better. The tensioner and chain length looks to be ok, clean and stiff/springy. I did fold/unfold it roughly a few times and could not get the chain to jump off. I will let the rider have a play with the bike and report back.