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No front DR - chain jumping off ring

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No front DR - chain jumping off ring

Old 10-11-12, 08:28 AM
  #1  
ILClyde
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No front DR - chain jumping off ring

I've decided it's time for my 25 year old Fisher Hoo Koo to live a second life as an errand/town/family ride bike. In the process of converting it, I've stripped off the front DR. I took the small and medium chainrings off, leaving the 49T. I love the simplicity of this bike as a 1x6, but I've apparently created a new problem.

Now, sometimes (not always) when shifting the rear DR, the chain will jump off the remaining chainring. I can't really pin it down to it consistently happening at any point in the rear cassette. Although I'm starting to think it's more likely to happen when pedaling harder.

What did I do wrong?

Thanks, in advance.
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Old 10-11-12, 10:02 AM
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Glynis27
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That's pretty normal when doing that type of conversion. Previously the FD was keeping the chain in check, but now it's gone. You have a few options...

-Add a chain retention device or chain guide.
-Move chainring to middle position to get a better chainline. Add a bashguard in the outer position.
-Replace the front ring with a SS specific model (usually have taller teeth to hold the chain on).
-Don't shift under power or while going over rough terrain or bumps.
-Shorten chain (if possible) or use single-speed chain with taller side plates.

You may need to do a combination of these options or do something I haven't mentioned. Hard to say without being there.
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Old 10-11-12, 11:10 AM
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Retro Grouch 
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If it was my bike, and I hadn't tried the chainring in the middle position, that's what I would try first. If you lay a straight edge across your chainring, you'd like for the straight edge to exactly bisect the cassette.

If that wasn't enough to stop the chain from unshipping, I'd reinstall the front derailleur without the cable or shifter and dial in both limit screws until the derailleur cage was centered on the chainring.
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Old 10-11-12, 06:24 PM
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dsbrantjr
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http://www.paulcomp.com/chainkeeper.html
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Old 10-11-12, 07:01 PM
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Originally Posted by dsbrantjr View Post
I thought about that too, but it's a 25 year old HooKoo being repurposed as a single speed beater. The Paul chain keeper would definitely be more elegant, but I shudder to think how much one could cost.
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Old 10-11-12, 08:31 PM
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Originally Posted by Retro Grouch View Post
...I shudder to think how much one could cost.
They're $50.

I have an N-Gear Jump Stop, which is only $10, but it only stops the chain from coming off to the inside. I wish they would make a double-sided version of it, using the same mount!
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Old 10-11-12, 08:49 PM
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I love I'm not the only one who likes simplicity. I have a few "townies"...5 and 6 speeds, usually with just friction shifters, they are simple and can fly.

I'd reinstall the FD without the cable as suggested. You may do some digging around and find a smaller used one if your current FD is big and ugly.
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Old 10-11-12, 09:04 PM
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ILClyde
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Originally Posted by Turbo231 View Post
You may do some digging around and find a smaller used one if your current FD is big and ugly.
When I'm done with it the whole thing may be big and ugly! So, simple, cheap, big and ugly may just be a thing of beauty! Interesting on the Paul chain keeper and the Jump Stop, but I like the idea of just locking down the old DR.

Thanks for all the responses.
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Old 10-12-12, 01:11 AM
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David Grimshaw
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Hi Mr Clyde. I was wondering if this happens to be a Biopace chainring? I had a mountain bike in 1989 with Biopace chainrings and had terrible trouble keeping the chain on the biggest/outer ring. I actually put a post here about it a month or two ago to try to work out what happened. I took it to several bike stores and they could not help me. I did not know much about bikes so traded it on another. But I am reasonably sure the trouble was partly the Biopace chain ring and your bike may be fitted with them if they are still the originals.
David.
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Old 10-12-12, 06:49 AM
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Originally Posted by Nel View Post
They're $50.
Cheaper than I thought. I'm ashamed to say how much I paid for a pair of Paul's Thumbies.
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Old 10-12-12, 07:08 AM
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Originally Posted by ILClyde View Post
When I'm done with it the whole thing may be big and ugly! So, simple, cheap, big and ugly may just be a thing of beauty! Interesting on the Paul chain keeper and the Jump Stop, but I like the idea of just locking down the old DR.

Thanks for all the responses.
Going back to the first reply: Buy a single speed chainring - no ramps, pins, and taller teeth. The middle position is probably best. Cost = less than $30. No derailleur or stop needed. Bashguard on the outer optional.
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Old 10-12-12, 07:33 AM
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I'd look at the chain line first, as already suggested. 5mm narrower made the difference for me on my 1x8 - I want the chain perfectly straight on one of the middle cogs.

That lined out, every once in awhile the chain would drop off the outside, when shifting to the 11 cog when there wasn't much tension on the chain. The chainkeeper linked in this thread would work, but I made one from a pipe clamp (p clamp) and aluminum strip which I think looks better.
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Old 10-12-12, 08:12 AM
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I've been through this with my bike. A single speed chainring fixes it without the need for a 'keeper'.

I love the simplicity of using just the rear derailleur. No more fiddling.
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Old 10-12-12, 09:37 AM
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Worn Chainring?
If it was a triple , reducing it to a single, the remaining chanring goes in the middle position.

you probably need the rest of the drivetrain fed new stuff .. cass't/FW, chain..

Last edited by fietsbob; 10-12-12 at 09:40 AM.
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Old 10-12-12, 02:00 PM
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Originally Posted by jim hughes View Post
A single speed chainring fixes it without the need for a 'keeper'.
Any recommendations on a brand and source? I need a 44 tooth 104BCD. Rennen and Salsa were the only two that I found...
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