Chain jumping off

[grey-beard]

Well, I keep loosing the chain over bumps, I'm assuming that the spring tension on the crappy, but cool looking old sunrace rear mech is the issue. Any ideas? I'll try shortening the chain, but other than that there's no adjustments I can make, are there?

 

[Spudalumps]

Where is the chain coming off? Is it off your cranks, confession time, I once put the chain rings in backwards and they would slip off on curbs etc… :S

 

[grey-beard]

I should have said, it's actually an ebike conversion, so it's a single narrow wide chainring and yes, that's where it's coming off. Very annoying.
I suppose the narrow wide system works better with a narrower chain, like 10 speed or more, this is only 7 speed. But I think spring tension is a major factor, or lack of it.

 

[TOMAS]

I should have said, it's actually an ebike conversion, so it's a single narrow wide chainring and yes, that's where it's coming off. Very annoying.
I suppose the narrow wide system works better with a narrower chain, like 10 speed or more, this is only 7 speed. But I think spring tension is a major factor, or lack of it.

You got a picture of the chainset/setup? With it being a conversion i'm going to have a punt that the chainline is off, possibly by a long way - if the chain is being forced to run sideways by a lot then it will come off a lot, even on a narrow-wide ring. What chainring are you running - do you happen to know what chain (width) it's designed for?

 

[grey-beard]

The chainline is actually pretty good, this isn't my first conversion, but it's the first using such an old rear mech, the spring tension is pretty poor and I can't see any way of improving it, other than shortening the chain.
What were those things called that you could get that added and extra spring?

 

[hamster]

I wouldn't shorten the chain any more, otherwise it will struggle to get onto the big-big combination. I would try a new mech instead of that cruddy Sunrace, which is a copy of a bottom end Shimano one.