chain jumps sprocket

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ratcycle

ratcycle

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My first chopper is having chain problems. The sprocket is a three piece crank and the rear is a bendix 18 sprocket. I have a rear derailuer cage to keep tension on the chain. What's going on is the 1/8'' chani keep's jumping the front sprocket. The chain is the right length and kind and there is enough tension. But I can't figure out why it keeps jumping the front sprocket all the the time. I get one full pedal revultion then it jumps the sprocket. What could be wrong?
 
derailers are supposed to pull chains left and right ("derail"). if theres no gear cluster, shorten your chain or replace the derailer with a singulator (i know surly sells them) or rig up an idler cog like on a tandem bike.

common reasons for a chain to slip on a single speed bike is a bent/loose sprocket at the crank or a misaligned rear wheel. could also be the spacing too either at the dropout or the crank.

if youve still got troubles, post a pic of your set-up
 
Are you using a front sprocket with the shifting ramps and pins? If so that can cause jumping, you want a single-speed sprocket up front on the triple, even then it sounds like the chain may not be the correct type, multi-speeds 3X6, 3X7, 3X8 etc typically use a 3/32" chain, the 1/8" will likely work badly with a ramped/pinned sprocket, downside is the bendix cog may not work with the 3/32" chain, the flip-side is replacing the front sprocket with a smooth SS sprocket that'll work with 1/8" chain will likely require a fairly good chainline.

The derailleur should be fine using it as a chain tensioner.
 
You had a previous thread to this viewtopic.php?f=3&t=21004&p=212256#p212256

11110911381.jpg


Can you post a picture of the bike as is? I assume your 3 piece crank came off a multi-speed bike that had a derailler originally. If so, you will need a different chainring up front to work with the 1/8" chain.

As stated above, if the chain tension is loose then there may be an issue. And check your chainline. If the chain is falling off the side, then your chainline needs to be corrected. Also check the front chainring (not cranks) to make sure it is not warped.
 
SURLY BIKES - CLICK LINK

what I call an idler cog is the little cog hanging from a bracket just behind the front crank sprocket
twinnsport.jpg



ill try to look again but i didnt think i saw a pic of the bike with the chain on it
 
Sounds to me as though you need to a. get your sprockets in line, and b. shorten your chain so that it has no slack. If you have a modern ramped front sprocket, a spring loaded tensioner(in your case a derailleur)is going to allow the 1/8" chain to "shift" off when it wanders, which it will, because it's too loose on the sprocket. If you have no room in your drop outs to adjust for chain length, an idler as mentioned by CCR will work.
 
OK, it doesn't look like a ramped sprocket, but is it straight, :? and is it in line with the rear sprocket? Your "tensioner" appears to be working as an "idler" as previously mentioned, and I guess you need it to keep the chain from hitting your frame. It pretty much has to be misalignment, whether a bent sprocket, or just not in the same plane, can't be seen in the photos.
 

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