Why does 'er indoors's ebike keep throwing its chain?

[swee'pea99]

I've tried adjusting the rear mech, and the pressure feels fine to me. The chain feels 'tight but not over-tight', even, as here, in the highest gear. Everything looks to be in order, as far as I can see. But it keeps losing the chain - 'mostly when I hit a pothole, or when I'm changing gear, or both'. It probably loses the chain once a trip, give or take.

It's a newish B'twin ebike, the mech looks like this:

...and if there's anything else I could add that might be useful, please say.

Thanks in anticipation for any advice/suggestions.

 

[Tigerbiten]

I assume the chain is falling off the inside of the chainring.
You didn't mention where it unships.
If I'm right then fitting something like a dog fang to catch the chain may help.

Luck ...........

 

[Once a Wheeler]

Looks well used. Suggest the jockey-cage spring may be weak or clogged up and so failing to tighten the chain quickly enough once a pot-hole has jerked the cage forward. Removing the derailleur mechanism, dismantling it and plunging all the parts in a paraffin bath overnight; followed by cleaning, re-oiling and reassembling might do the trick. If it doesn't, try a new spring. Doing this carefully should also cure any hard-to-see alignment problems. Good luck.

 

[wiggydiggy]

I had exactly the same issue, I had a couple of links taken out the chain to make it stiffer. It has happened once or twice since but not nearly as often as before.

 

[Gillstay]

Does the derailleur move smoothly or is it jerking and flicking the chain across as I have had one do this recently. I worked it out by getting the bike up to chest height and then watching as it changed. It was not easy though. Good luck.

 

[swee'pea99]

Thanks all, that's really helpful, and gives me some good leads.

Looks well used. Suggest the jockey-cage spring may be weak or clogged up and so failing to tighten the chain quickly enough once a pot-hole has jerked the cage forward. Removing the derailleur mechanism, dismantling it and plunging all the parts in a paraffin bath overnight; followed by cleaning, re-oiling and reassembling might do the trick. If it doesn't, try a new spring. Doing this carefully should also cure any hard-to-see alignment problems. Good luck.

I'll definitely give the spring another careful check, and clean it in situ. Have to say disassembly sounds like last resort territory. Hope it doesn't come to that!

I had exactly the same issue, I had a couple of links taken out the chain to make it stiffer. It has happened once or twice since but not nearly as often as before.

Now that I can do - and easily! Definitely worth a go. Come to think of it, I guess checking the chain for wear might be an idea. Funny how the bleedin' obvious can pass you by. Or me anyway.

Does the derailleur move smoothly or is it jerking and flicking the chain across as I have had one do this recently. I worked it out by getting the bike up to chest height and then watching as it changed. It was not easy though. Good luck.

As far as I know, all the changing is fine and smooth, but I'll ask.

I assume the chain is falling off the inside of the chainring.
You didn't mention where it unships.
If I'm right then fitting something like a dog fang to catch the chain may help.

Luck ...........

I shall ask.

What in the world is a dog fang?

Thanks again.

 

[ColinJ]

What in the world is a dog fang?

One of THESE.

 

[I like Skol]

Single chain ring?

Chain doesn't look particularly slack, but a side on picture of the rear mech with the chain on the largest sprocket then again with the smallest sprocket would be helpful.

 

[I like Skol]

Also, which gears does she tend to use the most? If anything like Mrs Skol then the thought of 'spinning' equates to working too hard and she chooses to sedately grind along in a tall gear. This is even more likely with an ebike where the motor assistance makes it easy for Mrs Pea to waft along in the tallest gears without much effort or working up a sweat. Unfortunately this means the chain is always in its slackest position and any resistance in the freehub can easily induce sag in the top run of the chain which will cause your problems. Check the freehub isn't getting a bit sticky. Pedal backwards with the chain on the smallest sprocket and see what happens.

 

[gbb]

Very quick and easy to check, make sure the spoke protector is firmly attached to the wheel and NOT contacting the cassette. I've had this, it had slipped between the two and as a result, when you stop pedalling, the rotation of the wheel is transferred to the cassette, carries the chain forward...and off because you've stopped pedalling.