Chain coming off

I have a new hub geared ebike (nexus 8 speed) I have had to take the bike back twice to the bike shop where it was purchased from in the last 3 weeks because the chain has come off both times in city traffic. The last time the chain took the chain guard off with it! I can get the chain back on as a quick fix but it has been very slack on both occasions.

Any suggestions on what could be the issue other than it is a new bike and chains "stretch"

Thanks

sounds like the chain is way to loose and needs links removed or the hub needs adjusting if that is a option on the frame.

The 'chains stretch' line sounds like BS to me. As SW says it needs adjustment. What bike is it? With more detail you may get more specific help.

If nothing else works you could fit something like this - but it shouldn't be necessary.

https://www.merlincycles.com/dmr-sts-simple-tension-seeker-45105.html?utm_campaign=googlebase-GB&utm_source=googlebase&utm_medium=shopping&utm_term=Road+Bike+Single+Speed+Components&gclid=Cj0KCQjwov3nBRDFARIsANgsdoFeO4BJfIMJDr7fQOIjR0r1HwxdD484k4LR7YjaaKA9_YwrrmfkqhgaAvyFEALw_wcB

There is no way a new ebike should have a chain that comes off - if the bike shop has had it back twice and it is still happening then they are not much good - or are ignoring you.

You do have rights to return it if they can't (or fail ) to fix it more than a couple of time.

 

I think you need to get awkward with them and threaten to return it under your consumer rights - then give them one more chance to fix it.

This is based on UK rights - elsewhere check!

 

BTW - if it is coming off the rear gears it could be the gear indexing that is the problem - but the bike shop should fix this in 2 minutes

Which bike do you have? a photo of the side of the rear axle area will help with advice, having said that it is clear the bike shop is failing to deal with the issue in an effective way.

There is no indexing on hub gears, the rear cog/gear is a single one and relies on internal ratios for gearing.

Likelihood is a chain length issue or if using a tensioner it may be out of alignment or bent.

If bike uses horizontal drop outs or an eccentric BB then adjustment is likley needed to take up chain slack, if chain is still too slack then alink or maybe two need removing. Chains do strectch but not by much and certainly not on a new bike in a matter of weeks.

If your bike uses a chain tensioner simlar to a derailleur then the tensioner should be vertical or slightly forward of vertical for correct tension.

 

I use an Alfine 8 with BBS01 and twin chain rings 32/48t, chain line is a wee bit out on the 48t but no issues with chain coming off.

Thanks for all your advice. The bike shop have listened and there is now a heavier chain on the bike. They have stated if it should happen with this chain they will replace the sprockets with longer toothed ones. It already feels a better ride. The bike is a Raleigh Centros and all the work has been done under warranty with no quibbles. Fingers crossed......

Crank drive bikes are hard on chains and alloy frames don't take too kindly to a lot of rear wheel adjustments with that style of drop out.

 

I fitted a tensioner to mine, although at the time even that needed modifications to fit, now chain adjustment takes seconds via the allen headed bolt.

Two things spring to mind . Is/was the plastic spoke protector secure. Cheaper ones dont secure particually well and can come loose and wedge between the rear sprockets and the hub motor. The effect of this is it jams the freewheel so as you stop pedalling, the cranks stop but the rear sprockets keep rotating when they shouldn't, this causes slack in the chain, a droop, then it will come off when you start pedalling again.

 

Or maybe the freewheel isnt freewheeling very well causing a similar problem .

 

Just possibilities.

I have a new hub geared ebike (nexus 8 speed)

 

Two things spring to mind . Is/was the plastic spoke protector secure. Cheaper ones dont secure particually well and can come loose and wedge between the rear sprockets and the hub motor. The effect of this is it jams the freewheel so as you stop pedalling, the cranks stop but the rear sprockets keep rotating when they shouldn't, this causes slack in the chain, a droop, then it will come off when you start pedalling again.

 

Or maybe the freewheel isnt freewheeling very well causing a similar problem .

 

Just possibilities.

although I had set my chain up correctly I did find that it jumped off now and again. I bought a chain guide that fits on the seat tube where a front derailleur would go. It solved the problem. It is possible to use a front derailleur without cable and adjust the stops so it keeps the chain on the front ring.