Chain: Tight-Loose-Tight...

Hello all, I don't usually post coz I'm pretty savvy on the mechanics thing but this is puzzling me!

Whilst turning the pedals, my chain goes from being super tight and grinding, to loose enought to flip off, then tight again!

Obviously something is out of line, but what?

I recently changed my chainring and have tried it in 3 different positions so far, making sure that it is centered correctly (and yes its the correct BCD) and it's not solved it. My chain was never noisy before, now it's terrible.

I tried flipping the BB over incase something was bent there, but no change.

Help please!

Cheers
D!

your chain ring sounds like its not true/round. i.e off-centre, oval etc.

It's brand new dude! How would I check?

put the ring at the tightest position, slightly undo the chainring bolts, the ring might pull back a bit, then do up.

With the chain on or off?

is it a road ring (3/32) or track specific? is it resiting on the shoulders on the spider arms or floating on the inside? a lot of new rings can be oval etc, track stuff tends to be better engineered as the chain tension is crucial.

what murts said, with the chain on.

With the chain on or off?

what you wear whilst doing bike repairs is of no concern to us young man!

theres a guide on sheldonbrown how to sort this, although it could be your chainring isn't round. Is it a good ring or a cheap one?

TS Specalities Track ring, brand new from Condor on a Miche Advance Crank.

what you wear whilst doing bike repairs is of no concern to us young man!

Stylist!

that's you, that is :^}

You checked there is no lateral play on the cranks, the rear wheel is aligned and true (it's no straight) and the chain hasn't got any tight links?

that's you, that is :^}

Slamm and Sano ;)

Make sure you haven't got a well hidden bit of roadkill or part of your finger wedged onto the chainring.

With the chain on or off?

off you donkey, how the hell are you gonna find the tight spot on the chain, if it's on the floor?? huh? huh??

ask it for £5?

i don't know what to suggest, other than the possibility that the frame isn't true, but thats wack.

Wheel is straight, chainline is good, crank bolts are tight and there is no play. Just tried loosening the bolts and doing them up again, and it;s the same! :(

Might try spining the ring around again!

It's brand new dude! How would I check?

Take the chainring off and place on a a sheet of paper.

Mark the outline and the inside of the arms. Rotate the chainring around one arm at a time and see if at any point the outline doens't match up. If so, it's out of round and the cause of your problems.

cheap sprocket?

very, very rarely will you find a combo 100% perfect, all prts : b/b, crank, frame, rear cog, front cog will be absolutely perfectly round.

that's you, that is :^}

That was a fun day out! We should do it again soon Wayne :)

cheap sprocket?

Nope! All quality parts. Next Q

Are the crank bolt holes in the spider drilled to give proper alignment? I've seen spiders where all the holes are off to one side a bit - no fixing that.

Duncan, Are you bringing the motorbike this time?

did you make a sacrificial offering to tynan? said the magic words? etc etc