help with chain tension chainrings
#2
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If you can't deal with it, the only way is to get a new crank and chainring.
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Originally Posted by jbgladstone
Does anyone know how to check if the BB is causing the uneven chain tension?
https://www.sheldonbrown.com/straighten-chw.html
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Everyone except those riding with very expensive, precision manufacured track components has to deal with some variation in tension around the rotation of their cranks. From your description though it sounds like you have too much of it to be safe, and your chain definitely might fall off. But to be sure, try and derail it yourself, BEING REALLY CAREFUL not to AMPUTATE YOUR FINGERS. As long as your chainline is good and you can't derail it by hand, it might be rideable for now.
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Looks like a distant cousin of the crank I used to have. Probably the ring was mated to the arm off centre.
In other news, it is pretty likely that the ring will separate from the arm (well, develop play first...) sooner or later, especially if you're heavy and/or skid. Mine fell apart even though I'm light and never skid. These things don't stand up to brutal back-and-forth forces. Mind you, even the ultra-expensive CF cranks fall apart under brakeless fixed riders.
Long story short: best plan would be to get a new crank and transplant this one into a singlespeed bike where it could live longer. Or ride it into the ground and come up with a plan after that.
BTW, it's easy to check that the chain tension problem comes from the crank and not a bent rear axle. If the chain's loose/tight cycle is in synch with the crank rotation, it's the crank.
In other news, it is pretty likely that the ring will separate from the arm (well, develop play first...) sooner or later, especially if you're heavy and/or skid. Mine fell apart even though I'm light and never skid. These things don't stand up to brutal back-and-forth forces. Mind you, even the ultra-expensive CF cranks fall apart under brakeless fixed riders.
Long story short: best plan would be to get a new crank and transplant this one into a singlespeed bike where it could live longer. Or ride it into the ground and come up with a plan after that.
BTW, it's easy to check that the chain tension problem comes from the crank and not a bent rear axle. If the chain's loose/tight cycle is in synch with the crank rotation, it's the crank.
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Probably the ring was mated to the arm off centre.
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Looks like that was originally a road double, with the inner ring removed those things aren't very strong. A kid completely crumpled one at the sprints in chicago last year, very nasty. I won't use cranks like that any more after seeing that failure.
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Originally Posted by Landgolier
Looks like that was originally a road double, with the inner ring removed those things aren't very strong. A kid completely crumpled one at the sprints in chicago last year, very nasty. I won't use cranks like that any more after seeing that failure.
Not a road double, just a cheap singlespeed crank, kind of like this Dotek $20 special I got from my LBS
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Originally Posted by jbgladstone
I think that my cheap new chainring is not circular resulting in uneven chain tension. I can adjust the overall chain tension by moving the rear axel in the horizontal dropouts. But when the cranks are rotated, the tension is not constant. At the most loose point of the cycle the chain flexes about 2" (51mm) when the tightest part of the chain is adjusted to flex 0.5" (13mm).
This results in a noticably noisy drivetrain and "lumpy" feel. I am worried the chain will fall off Do I need a new chainring set up?
This results in a noticably noisy drivetrain and "lumpy" feel. I am worried the chain will fall off Do I need a new chainring set up?
Swaged cranks are not designed to withstand the two-way torques of fixed gear use, and even if it was concentric, it would not be suitable, because the small diameter swaged joint between the arm and the chainwheel is liable to fail.
I learned this the hard way 30 years ago, when I had a Sugino Maxy crank on my Raleigh International. Going down a hill, the chainring suddenly started to slip and spin around the swaged connection. I was a fair ways from home at the time, and it wasn't easy getting home. I could pedal on the flats, but as soon as I got going up even a slight grade, the chainwheel would slip. It was sort of like driving a car with a toasted clutch.
That's a very cool looking frame, by the way.
Sheldon "Forged Not Swaged" Brown
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I can imagine how that must've sucked. I rode 20km once with a bent fork and wheel. The bike wouldn't track straight at all.
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Good luck finding a 165mm for cheap. Older road cranks can be had for pennies. The 600 crankset I run on my conversion cost me $20, plus another $20 for the chainring.