Uneven chain tension and a can of beer

I´ve had an idea that I´m going to try tonight, I´ve got good quality cnc sprocket and chainring but i´m having problems getting even chain tension through the full rotation of the cranks. If you look closely at the crank/chainring, you can see that the c/ring isn´t sitting dead centre and there are gaps that vary in size between where the c/ring rests against each of the five arms of the crank.. . .anyway, I reckon that a bit of shimming from a ally can should do the job.

I´ve seen a few threads about this, different ideas have been thrown about but I´ve never seen anyone mention shimming, has anyone tried it?

Never needed to. Do your chainring bolts match the chainring? That is, are they from the same manufacturer?

Yes, both from sugino. There´s always going to be a bit of slack/play (call it what you want) as neither the chainring to the crank, nor the bolts to the crank are a press fit, so I´m not surprised it ain´t perfect. Personally it annoys me a bit, and I reckon I can make it better, we´ll see!

maybe a bent bb?

Have you tried

http://sheldonbrown.com/fixed-conversion.html#tension

Mine's the same. Annoys the shit out of me. Should probably just buy a better one, but when I start thinking like that a whole new bike starts to build itself in my brain.

a whole new bike starts to build itself in my brain.

So go with the flow...

Have you tried

http://sheldonbrown.com/fixed-conversion.html#tension

I've just tried the link (it works).
Pretty good advice for centering your chainwheel, to even up the tension through the full revolution of your cranks

I've just tried Sheldon's idea to limited success having changed the bb, chainring and sprocket but still the chain binds tight then slackens off. It's noisy and annoying. Before I look into new cranks is it more likely the frame is pissed? How can you be sure it's worth getting your steel frame realigned and what exactly would be done? Thanks for any insight.

Unlikely a bent frame would do that. It's not a moving part.

My ultegra cranks and dura-ace cog aren't perfect, it's just how it is. Do the sheldon trick though (you've tried, but try harder), helped a lot, i even used it to use the tightspot to my advantage, via having it tight when my chocolate foot is forward, for uber trackstands.

I had this problem, shimming works temporarily. Long term I bought some Sug 75's and bb to suit..

use search, loads of chain tension threads on this forum

Yeah, like this 7 month old one I pulled up. Just thinking about frame alignment though but guess thats neither here nor there. I'll tinker more, like your idea fatpants as that's when the slack is most noticable.

edmundane, served. lol.

Yeah, i'm not just an ugly face :P You may end up getting PERFECT eccentrication (made up words ftw?) accidently doing that too.

I use the Sheldon method, more or less.

Put the bike upside down, turn until you find a tight spot, slacken bolts but not completely just enough to allow the chainring to move if it receives a tap, then tap the chain to move the ring slightly - because it is at a tight spot it should move the chainring slightly in such a way to remove some of the tight spot tension, then tighten bolts a little, rotate again to see if there is still a tight spot then begin again if yes. Aim to have a significant improvement, not perfection.

This has worked for me.

Afterwards when you position the wheel do in a way so that there is a little slack in the chain when you feel with your fingers, but not enough that you can feel movement when you check by moving the cranks backwards and forwards. The wheel should turn freely, check over the whole rotation as a really tight spot left will potentially damage bearings and also increase drive train resistance (of course).

Fuck all that.

I like tight spots.

Fuck all that.

I like tight spots.

I find the loose spots worse, especially going over a cattle grid which can derail the chain!

Re-jigging chainring for tightspot in trackstand position for the win!

You really shouldnt shim. Most likely your bb and cranks setup arent "dead centre" themselves.
The sheldon method is kind of based on that and the play between chainring and crankarms is the easiest way to get it straight.

If you dont seem to get it okej you should check your rear wheel. Worn bearings/cones can make the hub/sprocket move while spinning and even the slightest movement fucks up the chain tension. Easiest way to check might be using another wheel, preferebly with the same cog you want to use with the first wheel.

So.. fuck you!