Multi to Single Speed

[teh603]

Ok, I'm back after another long break. My fiancee now has a bike. A troubled one.

It had a weird multispeed system where the derailer was built into the tensioner, except something was broken inside of it and the chain wouldn't shift into a higher- numbered gear. I stripped it out and shortened the chain so now it's a single, but I'm still having trouble with the chain popping off the sprocket and onto a smaller one. This happens even when the tension is set properly.

My first guess is that I need to break down the stack of sprockets on the hub and put the one we want to use in between two larger ones, but I'm not sure that'd be the best of ideas right now.

Anyone got a better idea?

 

[deorman]

You probably need to improve your chain line, if you can swap the cogs out put the one you want in line with the drive sprocket.

 

[Duchess]

Without seeing it, I would skip the derailleur and run it like a regular single. Whatever you want to run as a sprocket you want as close in line as possible. If the dropouts are more the vertical kind, you might not be able to ditch the tensioner, but it will still need to be inline. If the tensioner thing isn't able to be aligned, you might be able to replace it with a simple tensioner that's just a sprung pulley and align that.

 

[G-Matt]

It sounds like the rear & front sprocket may not be in line . Maybe you can eye ball it rear to front & move your front sprocket into the in the proper direction.


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[us56456712]

I ditch the derailleurs and use the small front chain wheel. Then I put the chain on the rear cog I want, usually a middle one and I have never had a problem. If you have the proper type of drops outs you can adjust the chain tension. Looks kinda funky but it works.

 

[Wildcat]

Post up some pics of the bike, showing how the chain is aligned.

 

[horsefarmer]

I just picked up an old 18 speed mountain bike and the chain jumped the front sprocket to the small ring (there is no front derailleur) I was researching possible causes and I understand an excessively stretched chain can cause it to jump sprockets. I have not checked the chain yet though. I believe they say you count 12 links and measure the length if it is over 12 inches long that is how much the chain has stretched.

 

[GuitarlCarl]

Sight unseen? Hmm, sounds like chainline to me too. Probably aggravated by a stretched out junk chinese chain. Line them sprockets up and put a new chain on. Even a new cheap chinese chain is better than an old stretched out one.

Carl.

 

[horsefarmer]

I measured the chain tonight looks like 24 links = 12" long (it's stretched 1/8" per foot). Seems like the derailleur tensioner is at the far end of its travel and I don't run on the largest front sprocket anyways, I shortened the chain 4 links. Will report back after riding it a few days if chain stays on.

 

[horsefarmer]

Went 6 miles last evening. Shifting rear derailleur much smoother, and chain stayed on middle front chain ring! Also a strange rattle noise that I thought was coming up from the bottom bracket is now gone, I'm thinking maybe the jockey wheels on the tensioner were rattling cause the chain was too long.

 

[teh603]

Sight unseen? Hmm, sounds like chainline to me too. Probably aggravated by a stretched out junk chinese chain. Line them sprockets up and put a new chain on. Even a new cheap chinese chain is better than an old stretched out one.

This seems to have worked for now. I couldn't get the sprockets off, because it looks like the manufacturer used some kind of hyper-proprietary locking system to keep them on. So I straightened the chain as best I could and put it back on.

The nearest bike shop is a pretty far drive away and I'm a little short on money to be getting a new chain. If cost wasn't an issue, I'd have already yanked that freewheel trash off and put a coaster brake hub on.

 

[jerrykr]

A single speed 1/8 chain will help, as it's not designed to be as "flexible" side to side as a multi-speed chain.