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When pedalling the chain sometimes get stuck on the front sprocket. This happened after I cleaned the gears and replaced the chain. What could cause this?

The purple line is the chain. The circles are front and back sprockets.

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You can see the chain in the bottom of the images following the sprocket back up during rotation.

enter image description here

  • Chain and chainringwear are possible causes, but you installed a new chain and the rings don't appear to be badly worn (though the big ring is getting there). I'm wondering if you cut the new chain too long. – Daniel R Hicks Sep 30 '18 at 12:31
  • I've use the crankset for over 7000km so it's probably time to change it anyway. Would a longer chain cause it to get stuck like this? It's really stuck. I've to use quite a lot of force to get it off with my hands. I can't see any obvious hooks on the sprocket teeth, but I'll look more carefully tomorrow. – Oleander Sep 30 '18 at 12:36
  • I have seen cases where it was just one or two teeth that were the problem, and some work with a file fixed things up. – Daniel R Hicks Sep 30 '18 at 12:42
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    Further reading: 'chainsuck' – Swifty Sep 30 '18 at 13:32
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    It's really stuck. I've to use quite a lot of force to get it off with my hands. That doesn't sound like chain suck from a dirty chain, or even hooked teeth on your crankset (and FWIW, 7,000 km isn't very long in the lifespan of a crankset...) Is the chain getting jammed between the chainrings? If so, is it the proper chain for the crankset - it's not a 9-speed chain on a 10-speed crankset or something like that? – Andrew Henle Sep 30 '18 at 15:42
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One cause of this is chainring wear. The teeth become slightly hook shaped, which catches the chain rollers and pulls the links up around the chainring.

This will be exacerbated by introduction of a new chain. A worn chain gets slightly (in the order of 0.5 - 0.75%) elongated due to wear between the rivets and plates. The new chain, having slightly less distance between rollers is more prone to getting caught.

Look at you chainrings and look for signs of excessive wear, especially the one you use the most. Also look at the cassette sprockets, if you didn't change the cassette when you got a new chain.

  • Thanks I'll take a look tomorrow morning! The cassette is only 1400km old. – Oleander Sep 30 '18 at 12:24
  • "This will be exacerbated by introduction of a new chain" ... which isn't then adequately shortened – Lamar Latrell Oct 3 '18 at 6:44

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