Brompton chain issue.

[Willam]

Just changed the chain on my 6 speed Brompton, used an 8 speed chain, the chain jumps violently off when I change the gear to 3 on the internal hub, but only if I stop pedalling, if the cranks are moving the chain runs fine, it runs normally in 1 and 2 setting, any suggestions why this is happening?

 

[Gunk]

8 speed chain should be fine, are you sure it’s the correct length?

 

[Sharky]

Is it jumping off the chain ring or the sprocket?

 

[Willam]

8 speed chain should be fine, are you sure it’s the correct length?

Measured from the previous chain that came new on the bike, even doubled checked that a 50 tooth chain ring requires a 100 link chain.

 

[Willam]

Is it jumping off the chain ring or the sprocket?

It jumps violently from the top middle of the chain, up and down a few times then comes off the chainring, very weird as I was thinking the free wheel as this only happens when I stop pedalling but doesn’t do this when I’m in a lower gear and stop pedalling?
I’m thinking the sprockets are not the issues as I don’t change those, this is only when changing the internal hub gears.

 

[88robb]

Just changed the chain on my 6 speed Brompton, used an 8 speed chain, the chain jumps violently off when I change the gear to 3 on the internal hub, but only if I stop pedalling, if the cranks are moving the chain runs fine, it runs normally in 1 and 2 setting, any suggestions why this is happening?

The chain is likely too wide. An 8-speed chain can be slightly too thick for the internal hub's sprocket. When you stop pedaling in gear 3, the chain catches on the hub casing and jams. Fit a correct 6/7/8-speed chain to solve it.

 

[Willam]

The chain is likely too wide. An 8-speed chain can be slightly too thick for the internal hub's sprocket. When you stop pedaling in gear 3, the chain catches on the hub casing and jams. Fit a correct 6/7/8-speed chain to solve it.

it was a KMC 8 speed, the description says it’s compatible with 6/7/8 speeds?

The chain doesnt actually go into the hub so not sure what it could be catching on?

 

[Sharky]

Something I had, which is not dissimilar was ...

When I stopped pedaling, the freewheel did not "free", so the sprocket kept turning and the chain kept moving to the chainring and derailed.

 

[Gunk]

How old is your Brompton?

Reason I ask is that I’ve had a similar issue and solved it by changing the rear sprocket.

The earlier Bromptons had a 1/8” chain and sprocket. A newer 3/32” 8 speed chain doesn’t fit the 1/8” sprockets and will skip on the teeth.

Your bike may be fitted with original 1/8" sprockets which were discontinued in 2017. To replace the chain you need the 3/32" sprockets which were introduced in 2012.

It’s also good practice to change sprockets when you fit a new chain.

 

[Willam]

How old is your Brompton?

Reason I ask is that I’ve had a similar issue and solved it by changing the rear sprocket.

The earlier Bromptons had a 1/8” chain and sprocket. A newer 3/32” 8 speed chain doesn’t fit the 1/8” sprockets and will skip on the teeth.

Your bike may be fitted with original 1/8" sprockets which were discontinued in 2017. To replace the chain you need the 3/32" sprockets which were introduced in 2012.

It’s also good practice to change sprockets when you fit a new chain.

Just 1 year old…I just can’t see where the issue is coming from as essentially the chain is unobstructed from anything knocking it off, but it must be caused by something.

 

[silva]

I don't get how an internal hub's gear position can affect how the chain runs over the single external rear and front sprocket. The problem should occur in all gears, or not at all.

 

[fritz katzenjammer]

I’ve run into this before when servicing “ regular” bikes. If the chain was allowed to wear too long it will wear the sprockets ( cassette ) out. Then when a new chain is fitted it will skip on the worn sprocket teeth when under load. The fix is new sprockets.

third is the highest load gear so that’s why it shows up in that gear.

 

[Willam]

I’ve run into this before when servicing “ regular” bikes. If the chain was allowed to wear too long it will wear the sprockets ( cassette ) out. Then when a new chain is fitted it will skip on the worn sprocket teeth when under load. The fix is new sprockets.

third is the highest load gear so that’s why it shows up in that gear.

But the spockets are not used, it only happens with the internal hub gears where the chain doesnt touch.

 

[88robb]

it was a KMC 8 speed, the description says it’s compatible with 6/7/8 speeds?

The chain doesnt actually go into the hub so not sure what it could be catching on?

The chain might be rubbing the spokes because your derailleur's limit screw needs adjusting. Or, a chain link is stiff.

 

[Willam]

The chain might be rubbing the spokes because your derailleur's limit screw needs adjusting. Or, a chain link is stiff.

Doesn’t have a derailleur limit adjustment screw, there are just two sprockets which I don’t change, the issue happens just when I move to the 3rd internal gear from 2nd, I don’t change sprockets at all but the issue still happen

Edit correction I now believe it does have one on the chain pushing thingy. T