Why is my chain skipping in the 12t sprocket?

[MontyVeda]

So I'm having a head scratchy moment with this... chain skipping is either a stretched chain or a worn gear, but this is a brand new chain and a brand new cassette (new back wheel too).

The indexing is good and everything works when the bike's upside in the workshop (kitchen), it's only when riding it slips intermittently, more so when pedalling lightly. It only happens on the small sprocket, the other six are fine.

Like i say, the symptoms suggest that something is worn and needs replacing, but it's all new.

 

[ColinJ]

Perhaps the endstop is set too far in, preventing the chain from fully settling on the smallest sprocket?

 

[C R]

So I'm having a head scratchy moment with this... chain skipping is either a stretched chain or a worn gear, but this is a brand new chain and a brand new cassette (new back wheel too).

The indexing is good and everything works when the bike's upside in the workshop (kitchen), it's only when riding it slips intermittently, more so when pedalling lightly. It only happens on the small sprocket, the other six are fine.

Like i say, the symptoms suggest that something is worn and needs replacing, but it's all new.

How new is the chainring? I think a worn chainring with the chain in the smallest sprocket is more prone to chainsuck than skipping, but I guess skipping would still be possible.

 

[Paulus]

I would look at the limit screw not allowing the rear mech to go over far enough. It will only be a slight adjustment as the chain is getting onto the sprocket.
A second thought, I'm guessing it's a cable operated system, so is the cable too tight so not allowing the mech to go over.

 

[ColinJ]

Perhaps the endstop is set too far in, preventing the chain from fully settling on the smallest sprocket?

Or there is friction in the cable so the derailleur is slow to move to its final position? Pedalling lightly could give a slacker chain to be snatched at by the second sprocket?

 

[fritz katzenjammer]

Is the chain on correctly, lettering side out. Is the smallest sprocket seated properly, look for wobble. Is there a damaged tooth on the sprocket. Is it the correct width of chain. Is the derailleur bent, or the hanger bracket. Use an alignment tool, you can‘t see a minor bend in the fore/aft direction but it can screw you up at one end of the cassette.

sound silly? I’ve encountered all of these issues on new installs which are acting oddly. Bike brought into out shop because somebody can’t figure out why something is skipping and it turns out something new was already damaged, was installed wrong or was bent.

actually… I’ve encountered all of these issues ( except wrong chain width ) on new bikes, fresh out of the box.

 

[a.twiddler]

"B" screw adjustment?

 

[MontyVeda]

Or there is friction in the cable so the derailleur is slow to move to its final position? Pedalling lightly could give a slacker chain to be snatched at by the second sprocket?

it's not trying to ride up onto the second sprocket (I'd hear it). it feels like the chain just isn't fully engaging with the little 1st sprocket and its rollers are riding on top of the teeth for a moment.

How new is the chainring? ...

only a few weeks old and ran perfectly until i put the new cassette on the new wheel

I would look at the limit screw not allowing the rear mech to go over far enough. It will only be a slight adjustment as the chain is getting onto the sprocket.
A second thought, I'm guessing it's a cable operated system, so is the cable too tight so not allowing the mech to go over.

The limit screw is correct. New cables and outers too since it's full service. They're all functioning as they should.

I figured it could be a few stiff chain links but I've got my hands mucky a few times trying to find them, but can't.

 

[MontyVeda]

"B" screw adjustment?

possibly.... that's the screw that i honestly don't know what its function is. I know what it does, i'm just not sure why but I'll look into it. Thanks

 

[ColinJ]

possibly.... that's the screw that i honestly don't know what its function is. I know what it does, i'm just not sure why but I'll look into it. Thanks

It is for the other end of the cassette. If the derailleur is too close to the biggest couple of sprockets when the chain is on them there can be problems. The B-screw can be adjusted to push the mech further away.