Chain being thrown....

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Dave 123

Legendary Member
I've had my Cube Agree GTC for 6 years. It's well looked after and certainly not abused.

A couple of years ago I asked this question-

Chain in the big ring. I'm not putting loads of power through the pedals, a sudden crunch and off comes the chain, falling in toward the bike frame.

I have had a new chain and cassette. I changed the big chainring recentlyas the teeth were worn. Last year I took it to Rutland Cycles, the mechanic said the hanger had been bent- he replaced it.

It has DI2 shifting.

At present I'm reluctant to ride it as I am afraid to ride out of the saddle at any point. I've been doing this on a couple of occasions and the chain has come off..... doesn't do your knees any favours!

Anyway, it came off again this morning, not under any particular load.

Any thoughts?
 

adamhearn

Veteran
I can't see how a bent hanger would cause a chain to come off in the way you describe...

What mechanical adjustments are there on the DI2 front mech? High/low limits may need tweaking [if they exist... I'm sure they must do!]. Maybe the shifter/junction box is throwing errant commands to the mech? Is the chainring true/is it flexing on the crank?
 
OP
OP
Dave 123

Dave 123

Legendary Member
I can't see how a bent hanger would cause a chain to come off in the way you describe...

What mechanical adjustments are there on the DI2 front mech? High/low limits may need tweaking [if they exist... I'm sure they must do!]. Maybe the shifter/junction box is throwing errant commands to the mech? Is the chainring true/is it flexing on the crank?
It all looks to be in line and running true. This afternoon I gave the chain a good old clean and lubed and wiggled all the links about. I'll see what that does.
 

Globalti

Legendary Member
Are you crossing the chain? That means using the big ring with big cogs on the cassette, effectively forcing the chain to change line four times in every revolution, which will wear it out very fast indeed and may be what's causing it to derail. From about the middle of the cassette inwards you should be dropping onto the small ring to maintain as straight a chainline as possible.
 
OP
OP
Dave 123

Dave 123

Legendary Member
Are you crossing the chain? That means using the big ring with big cogs on the cassette, effectively forcing the chain to change line four times in every revolution, which will wear it out very fast indeed and may be what's causing it to derail. From about the middle of the cassette inwards you should be dropping onto the small ring to maintain as straight a chainline as possible.

No. It happens when it’s in the middle of the cassette.
 

Globalti

Legendary Member
What about the chain tension? Is the chain too long or the derailleur spring too slack? Some RDs have an adjuster for tension.
 

Ming the Merciless

There is no mercy
Location
Inside my skull
Is it dropping off when you change gear or just dropping off after a few mins in that fear?
 

pclay

Veteran
Location
Rugby
I have a similar issue when riding downhill big front ring small rear cog. I have di2 as well, and the chain gets thrown off the front away from the bike.
 
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