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narrow-profile cog recommendation(?)

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Singlespeed & Fixed Gear "I still feel that variable gears are only for people over forty-five. Isn't it better to triumph by the strength of your muscles than by the artifice of a derailer? We are getting soft...As for me, give me a fixed gear!"-- Henri Desgrange (31 January 1865 - 16 August 1940)

narrow-profile cog recommendation(?)

Old 06-19-19, 10:56 PM
  #1  
agnewton
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narrow-profile cog recommendation(?)

Hi. As a first, fixed gear project, I'm converting an older 80s bike. I am trying to put a 16T cog on a threaded freewheel hub and I'm running out of threads for the lock ring (re-purposed BB lock ring). I can start the threads for the lock ring (maybe a thread and a half), but there aren't nearly enough to fully-engage the lock ring and tightening the ring will probably just strip the threads. The 3/32"-16T origin8 cog that I am bought is 7.3 mm wide. Can anyone recommend a threaded cog with a narrower profile (that would leave more threads exposed for a lock ring) that I could substitute? I plan to use thread locker on the cog and a front brake, but I am not experienced enough to judge whether I can overlook a lock ring with this setup. Does anyone with more experience have an opinion? Add a rear brake and a mouth guard? Thanks in advance.
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Old 06-20-19, 08:27 AM
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A lock ring serves little purpose on a normal freewheel hub. I would just use the cog you have without a lockring and use the following method to get the cog really tight. Install a front brake. You are unlikely to break the cog loose, but as long as you have a means of stopping nothing catastrophic will happen.


Last edited by mihlbach; 06-20-19 at 08:33 AM.
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Old 06-20-19, 08:57 AM
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I’m confused, are you using a multi-speed freewheel hub? Not a track hub? Because if so, you should have enough threading. Also, if you are, it won’t have any reverse threading for a proper lock ring, which I assume explains the use of a bb lock ring? I’m having a hard time imagining why you would t have enough thread for a fixed sprocket, but the ‘rotafix’ method suggested above ^^ is what you should do. Maybe also add some loktite for extra security? I sure hope you weren’t planning on doing skids with that setup. Use a front brake and you should be fine.

some photos of your hub and sprocket would be very helpful in properly addressing the problem.

Last edited by seamuis; 06-20-19 at 10:07 AM.
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Old 06-20-19, 09:43 AM
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I only have two freewheel hubs in my collection, but it was the same situation with them, only about 1 thread left after a cog went on. If my hubs were threaded all the way to the end, there might be enough for a BB lockring, but they're stepped down to an unthreaded section for the outer 1mm or so. Not sure if that's common or not.

If you're concerned, buy or build a wheel with a proper track hub. It's among the easiest wheels to build.
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Old 06-20-19, 10:27 PM
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Thanks for your replies. There is a 15-year Old Bikeforums Thread (fixed gear/ road hub- no lockring?) where someone had a similar problem and reading through it, I couldn't come to a conclusion on whether you could get away with skipping a locking. @mihlbach, the rota fix method looks like it will work and with a bit more torque than I'd get with a chain whip, but looks like it might be rough on the bb finish. @seamuis yes, it's a multispeed freewheel hub and yep, that's why the improvised BB lock ring. The ring leaves only a couple threads exposed when cranked on tight (photo below). In the old thread, someone said the Sheldon Brown website had info on cog dimensions. I only found it on the second trip to the site after scrolling down (Sheldon Brown- Chainline). Maybe a pre-2005 Surley would work, but I'm not sure where I could get one to try. I'll go with thread locker blue and avoid skids. @ThermionicScott, the hub is a late-model multispeed freewheel, maybe the older ones are threaded to the end. If the fixed gear experiment goes well, I'll build a proper wheel and use a frame without a derailleur hanger.

Thanks for your recommendations. Rota fix with thread locker and no skids.

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Old 06-21-19, 06:05 AM
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If your worried about damaging your bottom bracket finish, wrap it in a rag before you rotafix.
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Old 06-23-19, 12:41 PM
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Originally Posted by mihlbach View Post
If your worried about damaging your bottom bracket finish, wrap it in a rag before you rotafix.
Yeah exactly, just throw a rag over your bottom bracket and wrap the chain over it. That's what I do.
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Old 06-25-19, 07:57 PM
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Originally Posted by Philasteve View Post
Yeah exactly, just throw a rag over your bottom bracket and wrap the chain over it. That's what I do.
That'll be the plan (a rag and some muscle) for the final torque of the cog. I picked up the rear axle spacers this past weekend. My project for the next week will be to re-dish the wheel.

To satisfy some curiosity, I tried the track cog on a multi-speed hub from '70's (Maillard) wondering if there'd be more threads on an older hub. Nope. There is still only, at most, two exposed threads. Maybe an old, pre-2005 Surly cog or a cheap cog that's cheap because it has less threading/ material would do, but I'm going to stick with what I got for now.
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Old 07-04-19, 10:16 PM
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two week long weekend project... complete

Thanks all for the your input and replies. I re-spaced and re-dished the rear wheel last weekend. I used thread locker blue and put my 200 lbs into the chain whip to snug up the cog. 60 miles so far and no mechanical issues. In the spirit of "didn't happen without a photo," I attach two from my afternoon ride (taken just before the 40 minute delay for a downpour, thunder, and lighting). I've enjoyed my first fixed-gear rides and like the variety it has added to my mileage this week. The rear brake is redundant, but I didn't want to have to re-wrap and shellac the bars if this ride evolves; and it provides some security for my novice fixed-gear skills (descending on dirt roads is gonna take a bit more practice). Cheers.
drive-side profile


wheel-dish and chainline

Last edited by agnewton; 07-04-19 at 10:19 PM.
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