Something is bent?
 

I can't figure out what is wrong, or what has the bend. My chain is tighter at certain points in the rotation of the crank, but I can;t figure out if the front crank is bent or if it the rear hub that is bent. Also I don't think it would be because the axle isn't aligned correctly because then the chain wouldn't be loose at certain points and tight at others. I was about to order a new crank set but I thought I should ask first, any help is appreciated. Thanks.

Your chainring is probably not perfectly round, it's common. Try this.

"Dong tokes" FTW.

cool, now i know how to center chainrings.

His chain is bent. http://forum.blu-ray.com/images/smil...ported/umm.gif

It doesn't always work. Centering a chainring that isn't round to begin with won't make it so.

I have never bought into that "centering the chainring" argument. Seems to me the chain itself is the big collection of variables here. A couple hundred plates held together with a couple hundred pins...can you say "tolerance stackup"?

Statistically the error in the links should cancel out not add up.

A frankenchain may well have stretched and nonstretched sections. But my money is on the chainring offcenter and/or out of round. I see this frequently on homegrown ss/fg conversions that come in the co op.

TX,

Point taken.
But then connecting the ends of the chain together, and picking random segments to wrap around each of the cog and the chainring, would influence the tension on each unsupported side. The machining of the teeth on the cog and chainring now affect the tension of those segments, which will change as the crank is turned.

I think you have a better chance of eliminating a "cyclic" tightening/loosening of the chain if you pick a different set of teeth to wrap. The gear ratio is going to affect the "skid patch", ie the number of unique combos of teeth engaged at both the cog and chainring.

Runout is easy to check. It would seem to be difficult to make an "out of round" ring or cog, unless they are simply stamped.