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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)

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Old 10-04-10, 07:53 PM   #1
1nput0utput
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Chain Ring Slipping on One-piece Crank Arm

I'm not much for introductions, so I'm just going to jump in right here…

I've converted my old Varsity to singlespeed/fixed: new flip-flop hub, freewheel, fixed cog, chain, and chainring. I kept the original one-piece crank rather than using an adapter and installing a modern three-piece.

Here's my current puzzle to solve: The drive pin on the right crank arm is slightly smaller than the drive pin hole on the chainring. This causes the crank to slip slightly forward or backward when I resist the direction of the crank arms while riding on the fixed cog. For example, if I'm riding along forward and then resist the forward motion of the pedals, the crank slips backward until the drive pin meets the back side of the drive pin hole in the chainring. After I have stopped in this manner and I begin pedaling forward again, the crank slips forward until the pin is against the front side of the hole. (Of course this is never a problem when riding the freewheel because there's no resistance when backpedaling.)

The way to fix this seems to be to find some kind of bushing or washer that will fit around the drive pin to shim it up inside the hole in the chainring. The gap is very small, less than 2 mm, but I feel it in my legs every time the crank slips. Maybe someone here has done a similar conversion and has found a solution.

Last edited by 1nput0utput; 10-05-10 at 12:14 PM.
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Old 10-05-10, 01:29 PM   #2
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I wouldn't trust a shim in the drive pin hole not to break or slip out.
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Old 10-07-10, 10:20 PM   #3
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I cut down a piece of an aluminum can, folded it over a few times to make it the right thickness, and tapped it into the gap. It worked great for about ten minutes before I noticed that the slippage was back. The aluminum probably got compressed further by the drive pin and then fell out. I guess I need a better solution.

Maybe the drive pin could be brazed to the hole, but I think that would be rather difficult to undo when I have to swap the chainring again.
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Old 10-08-10, 02:56 AM   #4
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on my super sport,I mixed up some JB WELD packed it in the gap let it cure and wahlah no slipage.
also make sure your chainring is tight
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Old 10-08-10, 06:34 AM   #5
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I didn't know about J-B Weld, but it looks like that might do the job. I'm a little concerned about breaking the weld if I need to change the chainring, but I guess I'll worry about that when the time comes. Jbweld.net says it can be removed by grinding, filing, or heating.
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Old 10-08-10, 09:16 PM   #6
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It's a one piece crank and a Varsity. That stuff you can find anywhere for pennies. Hell if it was me, I would just weld the sprocket directly onto the crank. I know exactly what your talking about though with the sliding sprocket on the crank when running fixed. Just pick up american square tapered bb for under twenty bucks at most places or your LBS should be able to order you one. Then get something worthwhile.
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Old 10-08-10, 09:28 PM   #7
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It's a one piece crank and a Varsity. That stuff you can find anywhere for pennies. Hell if it was me, I would just weld the sprocket directly onto the crank.
+1

Personally would not use JB Weld or any other metal epoxies in this situation.
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Old 10-08-10, 10:12 PM   #8
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It's a one piece crank and a Varsity. That stuff you can find anywhere for pennies. Hell if it was me, I would just weld the sprocket directly onto the crank. I know exactly what your talking about though with the sliding sprocket on the crank when running fixed. Just pick up american square tapered bb for under twenty bucks at most places or your LBS should be able to order you one. Then get something worthwhile.
I didn't think there was an American standard for a square tapered bottom bracket. Do you mean a British or ISO standard bottom bracket?

http://sheldonbrown.com/gloss_bo-z.html#bottom
http://sheldonbrown.com/bbtaper.html

And if I understand correctly, an adapter would be required to fit a threaded bottom bracket into an OPC bottom bracket shell. I don't dislike the OPC, and I don't want to buy an adapter, a crank set, and pedals.

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Personally would not use JB Weld or any other metal epoxies in this situation.
Why not? Are you worried that it won't hold? If it doesn't, the worst that will happen is the crank will slip again.

In any case, I'll know tomorrow when I ride to work. I packed some J-B Weld into the gap earlier tonight, and it should be set tomorrow morning.
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Old 10-09-10, 06:37 AM   #9
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I don't know how good the JB would hold the items being chromed. I just dealt with this like two months ago on a Schwinn cantilevered frame I made into a fixie with original crank. There is a vintage ride I go on and a guy had a Surburban with three piece cranks and this style bottom bracket. It's actually cheaper then most adapters I've seen. I just remember them from my old BMX days and guys running Sugino cranks on their bikes and using these before they had adapters.
http://cgi.ebay.com/YST-square-tapered-spindle-BB-BMX-conversion-kit-/190415372972?pt=Cycling_Parts_Accessories&hash=item2c55a402ac

Last edited by Henry III; 10-09-10 at 06:41 AM.
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Old 10-10-10, 05:51 AM   #10
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JB weld is cheap and it works.were talking about a 1pc. crankset afterall.....not super high dollar parts.TRUST ME IT WORKS!!!























trust
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Old 10-10-10, 07:58 AM   #11
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Whether or not the JB Weld will fix the problem will all depend on whether you can find a good means of filling the gap with it so it'll stay in there. It is going to be hard to get it to actually stick to the chrome, so you'll want to feed it through then spread it out slightly on either side so it can't pull through. I bet it will eventually crack through from the compression, but it may last a while.

Welding would be tricky too in that you'd have to grind off the chrome, and it would be visible, but it probably would be a more permanent fix. It doesn't seem to make sense to get the adapter, a new bottom bracket, new cranks, and chainring since you're going for a Varsity conversion, not a frankenstein bike.
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Old 10-10-10, 09:44 AM   #12
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I had the same problem, and found out you don't even need to worry about JB Weld or arcwelding or shims, etc. Just take the crank and chainwheel off and tighten way down on the nut that holds the chainwheel in place and you'll be good to go. Tighten it WAY down, clamp the crank in a vice, put a 4 or 5 foot bar on the end of your wrench and go at it.
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Old 10-10-10, 10:25 PM   #13
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Originally Posted by Henry III View Post
I don't know how good the JB would hold the items being chromed. I just dealt with this like two months ago on a Schwinn cantilevered frame I made into a fixie with original crank. There is a vintage ride I go on and a guy had a Surburban with three piece cranks and this style bottom bracket. It's actually cheaper then most adapters I've seen. I just remember them from my old BMX days and guys running Sugino cranks on their bikes and using these before they had adapters.
http://cgi.ebay.com/YST-square-tapered-spindle-BB-BMX-conversion-kit-/190415372972?pt=Cycling_Parts_Accessories&hash=item2c55a402ac
I haven't seen that before. It would definitely do the trick. I'm not too excited about getting a whole new crank for this conversion, but good to know for the future.

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I had the same problem, and found out you don't even need to worry about JB Weld or arcwelding or shims, etc. Just take the crank and chainwheel off and tighten way down on the nut that holds the chainwheel in place and you'll be good to go. Tighten it WAY down, clamp the crank in a vice, put a 4 or 5 foot bar on the end of your wrench and go at it.
I thought about doing this, but I'll admit to being lazy and not wanting to take the bottom bracket apart again. Also, it seems like just tightening the cone nut might not be enough to hold a big ring in place. What gear ratio were you using on that bike? Mine is 48:18. I wonder if a higher ratio is more likely to move the chainring back and forth because it takes more force to turn the cranks.

In case anyone is curious, my first try with the J-B Weld didn't work as well as I wanted it to. I let it cure for twelve or thirteen hours and rode the bike the next day. It was perfect at first; no slippage. Then after a mile or two I noticed it was slipping again. Part of the hardened epoxy had cracked and a chunk fell out. Being the stubborn person that I am, tonight I packed some more J-B Weld in there, working around the leftovers from the first try. I used more this time, and I was more careful about making sure the epoxy would bond with all surrounding surfaces. I'm going to let it cure longer this time and try it out tomorrow.

If that doesn't work, I'm probably going to the hardware store to buy a vise…

Thanks to all of you for your help.
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Old 10-11-10, 05:52 PM   #14
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44:17. But actually, I think a lower gear ratio translates to more force on the components, rather than a higher one (At least I know this is true with rear cogs). If not, then I think the amount of force between the cone nut and the chainwheel won't be any more than the amount of force applied with your legs. I'd be more worried about sudden pressure, like skids.
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Old 10-11-10, 06:48 PM   #15
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I'd give it a 97.69% chance it's gonna slip again.
A. You'll toss it into a vice and strip the threads on the bearing cone.
B. You'll toss it into a vice and round off the edges of the bearing cone.

Three piece cranks can be found pretty cheap. I went to my LBS and scored a set of Shimano 600 and older Sugino cranks with chainrings and a set of beatup MKS pedals with clips for $30 for some other projects. Just ask to see if they have any old used cranks laying around. Not to mention you'll have a better selection of pedals going to a three piece setup and it'll probably weigh less also. I've got another pair of Shimano cranks you can have just pay for the shipping. I can't let someone ride around with one piece cranks on a fixie. It just kills the fixie mojo. lol
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Old 10-12-10, 09:08 AM   #16
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On what are you basing your 97.69% chance? Sounds like you've never tried, in which case you have no basis for making such a prediction (with 4 significant figures!).
If fixie mojo is to be simplistic and "one with the bike", and a couple benifits of fixed gear bikes being easy maintenance and durability, sounds like if anything adding a 3 piece crank would "Kill the mojo".
The additional pedal options is a selling point though.
No hard feelings, just sayin'...
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Old 10-12-10, 09:27 AM   #17
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Ashtabula cranks also use a different bb shell diameter which means you need an obscure adapter to get a normal ISO/JIS bb in there. It wouldn't really be worth the trouble, especially considering that one-piece cranks are not generally found on frames worth dropping much money on.
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Old 10-12-10, 09:47 AM   #18
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I'd give it a 97.69% chance it's gonna slip again.
It did slip again despite my best efforts with the epoxy.

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Originally Posted by Henry III View Post
Three piece cranks can be found pretty cheap. I went to my LBS and scored a set of Shimano 600 and older Sugino cranks with chainrings and a set of beatup MKS pedals with clips for $30 for some other projects. Just ask to see if they have any old used cranks laying around. Not to mention you'll have a better selection of pedals going to a three piece setup and it'll probably weigh less also. I've got another pair of Shimano cranks you can have just pay for the shipping. I can't let someone ride around with one piece cranks on a fixie. It just kills the fixie mojo. lol
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On what are you basing your 97.69% chance? Sounds like you've never tried, in which case you have no basis for making such a prediction (with 4 significant figures!).
If fixie mojo is to be simplistic and "one with the bike", and a couple benifits of fixed gear bikes being easy maintenance and durability, sounds like if anything adding a 3 piece crank would "Kill the mojo".
The additional pedal options is a selling point though.
No hard feelings, just sayin'...
I don't think I buy into the "fixie mojo" thing, but there are obviously good arguments on both sides of the argument between one-piece and three-piece. I've stuck with the one-piece for a few reasons:
  1. I already have it; no significant additional investment.
  2. It's very durable; more than thirty years old with no damage.
  3. I already have pedals for it that I like. Switching to a three-piece would mean getting 9/16" pedals.

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Ashtabula cranks also use a different bb shell diameter which means you need an obscure adapter to get a normal ISO/JIS bb in there. It wouldn't really be worth the trouble, especially considering that one-piece cranks are not generally found on frames worth dropping much money on.
I think Henry III's earlier suggestion of a cup/cone bottom bracket with a square taper axle would do the trick without an adapter: http://compare.ebay.com/like/1904153...=263602_304662

I'm trying not to spend too much more money on this frame because it's basically built up to what I want except for this problem with the chainring slipping.
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Old 10-12-10, 11:56 AM   #19
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I think Henry III's earlier suggestion of a cup/cone bottom bracket with a square taper axle would do the trick without an adapter: http://compare.ebay.com/like/1904153...=263602_304662
Right on, I hadn't actually looked at the link. My bad.
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Old 10-22-10, 03:05 AM   #20
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you can also just leave it alone,seriously I doubt it will hurt anything.or truvativ makes an adapter that allows you to run a cartridge BB ,so you can run 3pc.crankset
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Old 10-22-10, 04:13 AM   #21
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There is a lot of nonsense in this thread. You cannot use a square tapir BB without an adapter, which would not be worth the trouble on this cheap frame.

The only problem with the play you are describing is that it can loosen the bearing cone, which doubles as the lockring that holds the chainring in place. You should use a bit of locktite on the bearing cone to prevent it from working loose. As long as the bearing cone stays tight against the chainring, the little bit of play in your chainring is nothing to worry about. Its a cheap fixie conversion built out of junk parts...I wouldn't expect perfection.
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Old 10-23-10, 06:03 AM   #22
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thank god for cheap fixed gears!WHO SAID ANYTHING ABOUT PERFECTION ANYWAY.HE JUST WONDERED IF YOU COULD FIX HIS SLIPPING CHAINRING.
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Old 10-23-10, 06:10 AM   #23
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Originally Posted by 1nput0utput View Post
Maybe the drive pin could be brazed to the hole, but I think that would be rather difficult to undo when I have to swap the chainring again.
Solder? Easier to melt back out than brass, but anything short of gunsmith's silver solder (not the same as plumbing or electrical silver solder) might be too soft.
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Old 10-23-10, 08:54 AM   #24
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you can also just leave it alone,seriously I doubt it will hurt anything.or truvativ makes an adapter that allows you to run a cartridge BB ,so you can run 3pc.crankset
I know it won't hurt anything. It's just annoying. Even though it's slipping only a very short distance, it feels like a lot more through your legs while riding. As I mentioned before, I'm avoiding the adapter because I don't want to buy a cartridge bottom bracket, crank set, chainring, and pedals.

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There is a lot of nonsense in this thread. You cannot use a square tapir BB without an adapter, which would not be worth the trouble on this cheap frame.
Doesn't this cup/cone bottom bracket have a square taper axle?

http://www.yst-corp.com.tw/products_...o=200907290052

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The only problem with the play you are describing is that it can loosen the bearing cone, which doubles as the lockring that holds the chainring in place. You should use a bit of locktite on the bearing cone to prevent it from working loose. As long as the bearing cone stays tight against the chainring, the little bit of play in your chainring is nothing to worry about. Its a cheap fixie conversion built out of junk parts...I wouldn't expect perfection.
I hadn't considered that the slipping could loosen the bearing cone. But if it did loosen the cone, you would feel the bearing get tighter. I think that would be noticeable at least when turning the cranks by hand if not also while pedaling.

Perhaps the best solution will be to combine a few of the methods mentioned so far: tightening the bearing cone nut as much as possible against the chainring; using a thread adhesive on the cone nut to hold it in place; putting a shim in the gap between the drive pin and the hole in the chainring; epoxy, brazing, or soldering to hold together the drive pin, shim, and chainring.

Last edited by 1nput0utput; 10-23-10 at 09:00 AM.
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Old 10-23-10, 09:28 AM   #25
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It's a one piece crank and a Varsity. That stuff you can find anywhere for pennies. Hell if it was me, I would just weld the sprocket directly onto the crank. I know exactly what your talking about though with the sliding sprocket on the crank when running fixed. Just pick up american square tapered bb for under twenty bucks at most places or your LBS should be able to order you one. Then get something worthwhile.
Yup thats the thing to do, but weld it inside the BB, weld it right around the nut that tightens the chainring down to the ashtabula crank, that way you won't have an ugly weld to look at all day.
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