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Old 08-29-12, 08:27 AM   #1
wphamilton
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Chain guide - do you think this will work?

The problem: every once in awhile, if I shift into my highest gear while spinning out - the chain is slack - I'll drop the chain off the outside of the chain ring.

I have a 1x8 configuration on a road bike using a cheapo single chain ring, the kind where the drive side crank is solidly welded to the ring. On front I have the ring, the chain, and nothing else. This works fine and I never drop the chain inside, just rarely outside if I don't keep some tension on the chain. I shortened my chain slightly thinking it might add some tension, but that hasn't worked. I don't see any way a bash guard can be added to this ring and crank, but correct me if I'm wrong. S-Ram makes some very expensive solutions for track bikes I think, but I don't feel like splurging on this.

I know I could put an old front derailleur on and that would probably work, but that's a little goofy even for me. So I thought I'd go to the hardware store and get a P clamp for the seat tube and a short piece of steel bar or long bolt, and just bend it back over and outside the chain just a few mm from contact. Or maybe just two p-clamps, one for the frame and one for the chain, mimicking a FD. Before I experiment though, do you think that will work or would it risk ripping things to pieces? Is there a reasonable off the shelf solution? Maybe a chain tensioner I can install on front?
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Old 08-29-12, 08:40 AM   #2
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Shift into your big-big (OK, big-only) combination and see if there is still some slack in the rear derailleur travel. If there is remove enough chain links to just allow shifting into the lowest gear safely. Unless you have a very limited rear derailleur or your biggest cog is huge, you should never have slack in your highest gear unless the chain is much too long.
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Old 08-29-12, 08:47 AM   #3
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Did that HillRider, I used the no-slack plus two links without derailleur method originally, which looked to me like a half-link too long, and later took two links out. The cassette range is pretty big, 11-30, but shifting is good.

ps by "highest" I mean the 11 tooth cog.

Last edited by wphamilton; 08-29-12 at 08:58 AM.
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Old 09-01-12, 09:48 PM   #4
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Not as pretty as I'd envisioned, but we'll see if it works at least.



Please pardon the dirty parts ...
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File Type: jpg chain guide.jpg (42.0 KB, 42 views)
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Old 09-02-12, 04:42 AM   #5
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http://www.paulcomp.com/ckclamp.html

I have one of these on my 1x9 bike.
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Old 09-02-12, 05:03 AM   #6
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Not as pretty as I'd envisioned, but we'll see if it works at least.

.
That looks less goofy to you than a front derailleur with the limit screws dialed in to hold it where you need?
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Old 09-02-12, 07:06 AM   #7
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Is there a reasonable off the shelf solution?
Paul's chain keeper is pretty tidy... but darn spendy if that price is typical.
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Old 09-02-12, 07:26 AM   #8
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That looks less goofy to you than a front derailleur with the limit screws dialed in to hold it where you need?
I suppose it has the advantage of looking intentional, not that he just "forgot" to remove the fd. I think a neater one could be made from a fd braze-on adapter clamp with a retaining bracket bolted on in place of the fd. It would be a lower cost, home made version of the Paul chain keeper Kimmo referenced.
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Old 09-02-12, 09:01 AM   #9
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That looks less goofy to you than a front derailleur with the limit screws dialed in to hold it where you need?
Sure! A long lever arm held under tension balanced by a wire, just to hold a cage in place is to me extremely goofy, rube goldberg. I'll replace that metal bracket some time, it's just all I could find in the cabinet. Or take apart an old FD like hillrider suggests ... which needs a longer clamp because of the angle ... nothing is easy without lots of spare parts and a machine shop
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Old 09-02-12, 10:09 AM   #10
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Sure! A long lever arm held under tension balanced by a wire, just to hold a cage in place is to me extremely goofy, rube goldberg. I'll replace that metal bracket some time, it's just all I could find in the cabinet. Or take apart an old FD like hillrider suggests ... which needs a longer clamp because of the angle ... nothing is easy without lots of spare parts and a machine shop
Don't use the wire. Install the front derailleur and dial in the low limit screw until the cage is where you want it.
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Old 09-02-12, 10:36 AM   #11
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You're right but my objection with a front derailleur is it's over-engineered for the purpose, and would be silly if you designed a chain guide that way. Evidently I'm as ocd about some things as other cyclists, just different things I guess.

I wonder about wrapping a chain cover over that and maybe mounted or wrapped to the bottom of the down-tube. If nothing else a strip of aluminum or polycarbinate. Or split some conduit?

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Old 09-02-12, 10:36 AM   #12
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When you want to throw some money at the thing,
a disc chainguard on the outside looks nice..
and either a second one on the inside of the single CR, or a chain-minder ,
to stop the unshipping on the inside..

I have a big one for my small wheel IGH setup which has a chain-tesioner,

Small ones are made for a Cyclo-cross bike option, 44,42t..

Paul's is a California manufacturer, rather than an exported idea ,
re imported from Asia. that is why his stuff costs more .

Last edited by fietsbob; 09-02-12 at 10:44 AM.
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Old 09-02-12, 10:49 AM   #13
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That would be ideal, involving replacing the ring and cranks unfortunately. I'm hesitant to pay Paul's prices. Any decent priced 44-46 tooth ring with double guards would work for me though.
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Old 09-02-12, 11:04 AM   #14
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Maybe you could fashion a constructeur-style FD that doesn't move. Then it'd be fairly light and keep the chain from going anywhere:



From http://bikeville.blogspot.com/2010/0...erailleur.html
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