Bicycle Mechanics - SS chain tension

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ryanwood
08-21-11, 02:37 PM
I have an early 80's schwinn road bike that I have converted single speed, but I am having chain tension issues.

The bike is equipped with semi-horizontal dropouts so I am not running a chain tensioner. As the crank spins, the chain gains and loses tension. It's not enough slack to cause the chain to skip, but it is pretty close.

I have inspected the chain and there are no stuck links so I ruled out the chain. I swapped out the crank and chain ring and still the same issue. I swapped the bottom bracket and that didn't fix it. The tension changes whether I am pedaling forward or spinning backwards with the rear wheel stationary.

I have tried everything I can think of, but I have gotten nowhere.

reptilezs
08-21-11, 04:06 PM
chainrings and freewheels are not perfectly round or centered. adjusts the tension in the tightest part of the rotation
FBinNY
08-21-11, 04:28 PM
+1, eccentric cranks are normal to varying degrees and act like cams causing the chain length to vary. If it's slight you simply accept it, but be sure to set the wheel so there's a bit of slack at the tightest spot.. The chain cannot ever be allowed to be tight.

If there's more variation that you'd like, you can try loosening the chainring bolts, then tightening them only firm. Rotate the crank to the tightest spot, and hit the front of the chainring (3 o'clock) with a soft mallet, or a hammer, through a piece of wood. Do this trial and error until you find the least eccentric position, then tighten the chainring to keep it there. Finish by resetting the rear wheel a bit farther back if possible.